LM8502
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SNVS592D – OCTOBER 2009 – REVISED FEBRUARY 2013
LM8502 Intelligent Lighting Management Unit That Fuses a 1.2A Dual High-Side Flash
LED Driver with a 10-Output Low-Side LED Driver
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FEATURES
DESCRIPTION
•
The LM8502 is a versatile LED driver suitable for
multiple applications. It includes a 2MHz, fixedfrequency synchronous boost converter, 10 current
sink LED outputs, 2 outputs for flash or haptic
applications, ambient light sensing and PWM input.
1
2
•
•
•
•
•
•
•
•
•
•
•
•
•
10 Programmable Low-Side Current Sinks with
Flexible Powering from VOUT or External
Voltage Source
1.2A Dual Flash LED Driver with Flash, Torch
and Voltage modes
Ambient Light Sensing Capability with Two
Inputs
Up to 4000:1 dimming ratio for LED outputs
Flash LED Thermal Sensing and Current
Scaleback
Hardware Flash, Torch Enable and Dual
Synchronization Inputs for RF Power Amplifier
Pulse Events
Haptic Feedback Motor Driver
Two Lighting Engines for User-Defined
Lighting Sequences with 48 * 16 Bits of SRAM
Memory
External Clock Pin for Power Save
External PWM Control Capability Enabling for
Example Dynamic Backlight Control
Fast I2C-Compatible Interface
General Purpose ADC for Measuring, i.e., LED
Output Voltages
Ultra-Small Solution Area < 32 mm2
30-Bump (2.42 x 2.77 mm x 0.6 mm) 0.4 Pitch
DSBGA Package
APPLICATIONS
•
•
•
•
The 10 current sink LED outputs offer individual
current control through an I2C-compatible interface.
Current can be accurately controlled with a full-scale
setting and 8-bit current control. The LM8502 also
enables LED control with group faders and lighting
engines. Group faders enable single I2C register
writes for multiple LED outputs with fading, whereas
lighting engines with SRAM memory enable enginedriven lighting sequences. Each LED output can be
powered either from VOUT or an external voltage
supply.
The flash function is capable of driving 2 LEDs, each
having 600 mA maximum current, or a single LED up
to a 1.2A maximum current. A hardware flash enable
provides a direct interface to trigger the flash pulse.
Dual TX inputs allow the flash to be synchronized
with the RF power system to prevent excessive
current draw from the system power supply. The
LM8502 also offers LED thermal sensing as a safety
procedure for flash and separate indicator LED.
The LM8502 has two inputs for Ambient Light
Sensing — together with the PWM input they enable
Dynamic Backlight Control. The LM8502 may also be
used for haptic motor driving instead of flash. When
the device is idle, featured Power-save mode and use
of an external clock reduce current consumption
significantly.
Camera Phone LED Flash
General Illumination in Portable Devices
Haptic Feedback Motor Driver
Fun Lighting
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2009–2013, Texas Instruments Incorporated
LM8502
SNVS592D – OCTOBER 2009 – REVISED FEBRUARY 2013
www.ti.com
TYPICAL APPLICATION CIRCUITS
2.2 PH
10 PF
VIN = 2.7V TO 5.5V
OUT
SW
D1
VDD
D2
10 PF
D3
TX1/TORCH
STROBE
D4
PWM/ENVM/TX2
D5
ALS1
D6
D7
Interrupt
LM8502
INT
External clock input for power saving
CLK
Trigger pin for lighting engine
TRIG
D8
D9
D10/ALS2
VBIAS
FLASH1
SCL
FLASH2
Flash 1.2A
SDA
LEDI/NTC
EN
GND
Figure 1.
5,77
CIN
VIN
TX1/TORCH
GND
PWM/ENVM/TX2
EN
COUT
GND
OUT
FLASH1
FLASH2
A5
B5
C5
D5
E5
F5
SDA
CLK
A4
B4
C4
D4
E4
F4
SCL
INT
A3
B3
C3
D3
E3
F3
TRIG
ALS1
A2
B2
C2
D2
E2
F2
A1
B1
C1
D1
E1
F1
D7
D9
D5
D3
D1
LEDI/ D10/ D8
D6
D4
NTC ALS
5.42 mm
SW
D2
Figure 2.
2
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SNVS592D – OCTOBER 2009 – REVISED FEBRUARY 2013
CONNECTION DIAGRAM
DSBGA Package
See package number YFQ0030SQA
5
5
4
4
3
3
2
2
1
F
E
D
C
B
1
A
A
Figure 3. Bottom View
B
C
D
E
F
Figure 4. Top View
Pin Descriptions
Name
Pin No.
FLASH2/VIBRAN
A1
High Side Current Source Output for Flash LED or Output for Haptic Feedback
FLASH1/VIBRAP
A2
High Side Current Source Output for Flash LED or Output for Haptic Feedback
OUT
A3, B3
Step-Up DC/DC Converter Output
SW
A4, B4
Drain Connection for Internal NMOS and Synchronous PMOS Switches
GND
A5, B5
Ground
D9
B1
LED Output 9
D10/ALS2
B2
LED Output 10 or Secondary Ambient Light Sensor Input
D7
C1
LED Output 7
D8
C2
LED Output 8
C3
Configurable as a High Side Current Source Output for Indicator LED or Threshold Detector for LED
Temperature Sensing (Leave unconnected if not used)
LEDI/NTC
Description
STROBE
C4
Active High Hardware Flash Enable. Drive STROBE high to turn on Flash pulse (Connect to GND if
not used)
VIN
C5
Input Voltage Connection
D5
D1
LED Output 5
D6
D2
LED Output 6
ALS1
D3
Primary Ambient Light Sensor Input (Leave unconnected if not used)
PWM/ENVM/TX2
D4
Configurable as PWM Input, an Active High Voltage mode Enable or Dual Polarity Power Amplifier
Synchronization Input (connect to GND if not used).
TX1/TORCH
D5
Configurable as an RF Power Amplifier Synchronization Control Input or Hardware Torch Enable
(connect to GND if not used).
D3
E1
LED Output 3
D4
E2
LED Output 4
INT
E3
Interrupt for MCU (Leave unconnected if not used)
CLK
E4
External 32 kHz Clock Input (Connect to GND if not used)
EN
E5
Enable/Reset
D1
F1
LED Output 1
D2
F2
LED Output 2
TRIG
F3
Trigger Input/Output for Lighting Engines (Connect to GND if not used)
SCL
F4
Serial Clock Input
SDA
F5
Serial Data Input/Output
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LM8502
SNVS592D – OCTOBER 2009 – REVISED FEBRUARY 2013
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BLOCK DIAGRAM
2.2 PH
COUT
10 PF
SW
OUT
VDD
CIN
10 PF
LEDI
BOOST
ANALOG SUPPORT
BLOCKS
(VREF, OSC, TSD, BIAS)
NOTE!
Flash outputs
are optional
with haptic
outputs
Vibra
motor
OUT_P
LEDI/NTC
OUT_N
+
1V
FLASH/HAPTIC
DRIVERS
FLASH1
FLASH2
PWM
GENERATOR
TX1/TORCH
IDAC AND LOW SIDE
LED DRIVERS
STROBE
CTRL
REG
GND
D1
D2
SCL
SERIAL
DATA
D3
CONTROL
SDA
D4
POR
PWM/
ENVM/TX2
D5
D/A
D6
EN
D7
CLK
D8
D9
ALS1
D10
ALS
ALS2 INPUT
INT
LIGHTING
ENGINE
TRIG
PROGRAM
MEMORY
LIGHTING
ENGINE
GND
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
4
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SNVS592D – OCTOBER 2009 – REVISED FEBRUARY 2013
Absolute Maximum Ratings
(1) (2) (3)
VIN, VSW, VOUT,VFLASH LEDS 1,2, VLED OUTPUTS, VLEDI/NTC (4)
−0.3V to 6V
−0.3V to VIN+0.3V with 6.0V max
Voltage on Logic Pins (Input or Output Pins)
Continuous Power Dissipation (5)
Internally Limited
Junction Temperature (TJ-MAX)
+150°C
−65°C to +150° C
Storage Temperature Range
Maximum Lead Temperature (Soldering) (6)
(1)
(2)
(3)
(4)
(5)
(6)
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under
which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed
performance limits and associated test conditions, see the Electrical Characteristics table.
All voltages are with respect to the potential at the GND pin.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office / Distributors for
availability and specifications.
Voltage spikes on SW pin can be higher than 6V.
In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may
have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP =
+125°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to-ambient thermal resistance of the
part/package in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).
For detailed soldering specifications and information, please refer to Texas Instruments Application Note 1112: Micro SMD Wafer Level
Chip Scale Package (AN-1112).
Operating Ratings
VIN
2.7V to 5.5V
Junction Temperature (TJ)
(1)
−30°C to +125°C
−30°C to +85°C
Ambient Temperature (TA)
(1)
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typ.) and
disengages at TJ = 135°C (typ.).
Thermal Properties
Junction-to-Ambient Thermal Resistance (θJA) (1)
(1)
60°C/W
Junction-to-ambient thermal resistance (θJA) is taken from a thermal modeling result, performed under the conditions and guidelines set
forth in the JEDEC standard JESD51-7. The test board is a 4-layer FR-4 board measuring 102mm x 76mm x 1.6mm with a 2x1 array of
thermal vias. The ground plane on the board is 50mm x 50mm. Thickness of copper layers are 36µm/18µm/18µm/36µm
(1.5oz/1oz/1oz/1.5oz). Ambient temperature in simulation is 22°C, still air. Power dissipation is 1W.
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Electrical Characteristics (1)
Limits in standard typeface are for TA = +25°C. Limits in boldface type apply over the full operating ambient temperature
range (-30°C ≤ TA ≤ +85°C). Unless otherwise specified, VIN = 3.6V, VEN = VIN.
Parameter
ISTANDBY
Current Consumption in Standby
mode
Test Conditions
Min
EN = 0, chip_en bit = 0
Typ
Max
0.3
Units
µA
FLASH OUTPUT SPECIFICATIONS
IFLASH1 + IFLASH2
IFLASH1 or
IFLASH2
Flash Current Source Accuracy
IFLASH1 or IFLASH2
IFLASH1 or IFLASH2
600 mA Flash LED
Setting
36 mA Torch Current
Setting
−8 %
1200
+8%
−10 %
600
+10%
−10 %
36
+10 %
mA
VHR
Current Source Regulation
Voltage (VOUT − VFLASH)
600 mA setting, VOUT = 3.75V
250
mV
IMATCH
Flash LED Current Matching
600 mA setting, VFLASH = 3V
0.5
%
tTX
Flash-to-Torch Flash LED
Current Settling Time (2)
TX Low to High, IFLASH1 + IFLASH2 = 1.2A
to 180 mA
20
µs
VIN_TH
VIN Monitor Trip Threshold
VIN Falling, VIN Monitor register = 0x01
(Enabled with VIN_TH = 3.0V)
VNTC_TRIP
NTC Comparator Threshold
VNTC_HYST
Hysteresis of NTC
LEDI/NTC bit = 1
2.8
3.0
3.2
−5%
1
+5%
HYST bit = 0
125
HYST bit =1
250
V
mV
HAPTIC OUTPUT SPECIFICATIONS
RPMOS
PMOS Switch ON-Resistance
800
RNMOS
NMOS Switch ON-Resistance
800
PWM
frequency
PWM on both channels (register
21H setting '11' for bits [4:3])
7.8
mΩ
kHz
STEP-UP DC/DC CONVERTER SPECIFICATIONS
IOUT = 0mA, Constant Voltage mode, 5V
setting
4.8
5
5.2
VOVP
Output Over Voltage Protection
Trip Point
On Threshold, 2.7V ≤ VIN ≤ 5.5V
5.5
5.6
5.7
Off Threshold
5.2
5.4
5.5
RPMOS
PMOS Switch On-Resistance
IPMOS = 250 mA
170
RNMOS
NMOS Switch On-Resistance
INMOS = 1A
130
ICL
Switch Current Limit
CL bits = 10
IOUT_SC
Output Short Circuit Current Limit VOUT < 2.3V
fSW
Switching Frequency
2.7V ≤ VIN ≤ 5.5V
IPASSMODE
Passmode Supply Current
Device Not Switching, chip_en bit = '1',
boost_en bit = '1'
VOUT_ACCU
Output Voltage Accuracy
1.7
2
mΩ
2.3
550
1.9
2
350
V
A
mA
2.1
MHz
µA
LEDI SPECIFICATIONS
ILEDI/NTC
(1)
(2)
6
Indicator Current
LEDI/NTC bit = 1
IND1, IND0 bits = 00
2.2
IND1, IND0 bits = 01
4.4
IND1, IND0 bits = 10
6.6
IND1, IND0 bits = 11
8.8
mA
Min and Max limits are guaranteed by design, test, or statistical analysis. Typical (Typ) numbers are not guaranteed, but do represent
the most likely norm. Unless otherwise specified, conditions for typical specifications are: VIN = 3.6V and TA = +25°C.
Guaranteed by design. VEN = 1.65V to VIN.
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Electrical Characteristics(1) (continued)
Limits in standard typeface are for TA = +25°C. Limits in boldface type apply over the full operating ambient temperature
range (-30°C ≤ TA ≤ +85°C). Unless otherwise specified, VIN = 3.6V, VEN = VIN.
Parameter
Test Conditions
Min
Typ
Max
Units
1
µA
LED DRIVER ELECTRICAL CHARACTERISTICS
ILEAKAGE
Leakage Current
Outputs D1 to D10
0.1
IMAX
Maximum Sink Current
Outputs D1 to D10 (with maximum fullscale current setting)
25.5
IOUT
Output Current Accuracy
(3)
(3)
IMATCH
Matching
VSAT
Saturation Voltage
Output Current Set to 17.5 mA
−5
mA
+5
Output Current Set to 17.5 mA
1
Output Current Set to 17.5 mA
45
65
%
mV
GENERAL PURPOSE ADC ELECTRICAL CHARACTERISTICS
(4)
LSB
Least Significant Bit
EABS
Total Unadjusted Error
tCONV
Conversion Time
VIN_TEST
(5)
VIN_TEST = 0V to VIN
(4)
DC Voltage Range
(4)
30
mV
±3
LSB
2.7
ms
0
5
V
LOGIC INPUT EN VOLTAGE SPECIFICATIONS (VEN = 1.65 to VIN unless otherwise noted)
VIL
Input Logic Low
VIH
Input Logic High
1.2
0.5
II
Input Current
−1.0
V
1.0
µA
0.2xVEN
V
1.0
µA
1.0
µA
LOGIC INPUT SCL, SDA, CLK, STROBE, TX1/TORCH, PWM/ENVM/TX2, TRIG
VIL
Input Logic Low
VIH
Input Logic High
II
Input Current
0.8xVEN
V
−1.0
LOGIC OUTPUT SDA, TRIG, INT
VOL
Output Low Level
IL
Output Leakage Current
IOUT = 3 mA
0.3
RECOMMENDED EXTERNAL CLOCK SOURCE (CLK) CONDITIONS
V
(4) (6)
fCLK
Clock Frequency
tCLKH
High TIme
tCLKL
Low Time
tr
Clock Rise TIme
10% to 90%
2
tf
Clock Fall Time
90% to 10%
2
(3)
(4)
(5)
(6)
32.7
kHz
6
6
µs
Output Current Accuracy is the difference between the actual value of the output current and programmed value of this current.
Matching is the maximum difference from the average. For the constant current outputs on the part (D1 to D10), the following are
determined: the maximum output current (MAX), the minimum current (MIN) and the average output current of all outputs (AVG). Two
matching numbers are calculated: (MAX-AVG)/AVG and (AVG-MIN)/AVG. The largest number of the two (worst case) is considered the
matching figure. The typical specification provided is the most likely norm of the matching figure for all parts. Note that some
manufacturers have different specifications in use.
Guaranteed by design. VEN = 1.65V to VIN.
Total unadjusted error includes offset, full-scale and linearity errors.
The ideal external clock signal for the LM8502 is a 0V to VEN, 25% to 75% duty-cycle square wave. At frequencies above 32.7 kHz
program execution will be faster, and at frequencies below 32.7 kHz program execution will be slower.
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Electrical Characteristics(1) (continued)
Limits in standard typeface are for TA = +25°C. Limits in boldface type apply over the full operating ambient temperature
range (-30°C ≤ TA ≤ +85°C). Unless otherwise specified, VIN = 3.6V, VEN = VIN.
Parameter
Test Conditions
FAST MODE I2C-COMPATIBLE TIMING SPECIFICATIONS (SCL, SDA)
Min
Typ
Max
Units
400
kHz
(7)
fSCL
SCL Clock Frequency
1
Hold Time (repeated) START
Condition
Fast mode
0.6
2
Clock Low Time
1.3
3
Clock High Time
0.6
4
Setup Time for a Repeated
START Condition
0.6
5
Data Hold Time
50
6
Data Setup Time
100
7
Rise Time of SDA and SCL
20+0.1Cb
300
8
Fall Time of SDA and SCL
15+0.1Cb
300
9
Set-up Time for STOP condition
600
10
Bus Free Time Between a STOP
and a START Condition
1.3
Cb
Capacitive Load Parameter for
Each Bus Line. Load of One
Picofarad Corresponds to One
Nanosecond
10
HIGH-SPEED MODE I2C-COMPATIBLE TIMING SPECIFICATIONS (SCL, SDA)
µs
µs
200
ns
3.4
MHz
(7)
fSCL
SCL Clock Frequency
1
Hold Time (repeated) START
Condition
160
2
Clock Low Time
160
3
Clock High Time
60
4
Setup Time for a Repeated
START Condition
160
5
Data Hold Time
0
6
Data Setup Tme
10
7
Rise Time of SCLH
10
40
Rise Time of SDAH
10
80
Fall Time of SCLH
10
40
Fall Time of SDAH
10
80
9
Set-up Time for STOP Condition
160
10
Bus Free Time Between a STOP
and a START Condition
160
8
(7)
ns
70
ns
Guaranteed by design. VEN = 1.65V to VIN.
10
SDA
6
7
8
1
7
2
SCL
1
5
3
4
9
Figure 5. I2C Timing
8
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TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 3.6V, Flash LEDs are OSRAM LW C9SP, White LEDs OSRAM LWQ38, COUT = 10 µF, CIN = 10 µF, L = Coilcraft
LPS3015–222MLB, TA = +25°C unless otherwise specified.
Boost Efficiency with Constant Current Load
vs
Load Current (Voltage Output Mode, 5V)
Boost Efficiency with Constant Current Load
(Voltage Output Mode, 5V)
99.0
95.0
IOUT = 100 mA
88.8
EFFICIENCY (%)
EFFICIENCY (%)
90.4
81.8
IOUT = 200 mA
73.2
IOUT = 500 mA
64.6
82.6
VIN = 4.2V
76.4
VIN = 3.6V
70.2
VIN = 3.0V
IOUT = 1A
56.0
2.5
3.0
3.5
4.0
4.5
64.0
0.1
5.0
0.3
INPUT VOLTAGE (V)
0.5
0.7
0.9
LOAD CURRENT (A)
Figure 6.
Figure 7.
LED Efficiency (OSRAM LWQ38)
Flash LED Efficiency
vs
VIN (Single Flash LED)
88.0
87.2
FLASH LED EFFICIENCY (%)
LED EFFICIENCY (%)
81.4
74.8
6 LEDs on
68.2
10 LEDs on
61.6
81.0
74.8
750 mA
68.6
600 mA
62.4
56.2
450 mA
300 mA
1 LED on
55.0
2.7
3.2
3.6
4.1
4.5
50.0
2.5
5.0
3.0
INPUT VOLTAGE (V)
Figure 8.
1.9
VIN
4.0
4.5
5.0
Figure 9.
Input Current
vs
(Single Flash LED)
83.0
750 mA
Flash LED Efficiency
vs
VIN (Dual Flash LED)
77.4
1.6
600 mA
EFFICIENCY (%)
INPUT CURRENT (A)
3.5
INPUT VOLTAGE (V)
450 mA
1.3
300 mA
0.9
66.2
525 mA
600 mA
450 mA
60.6
0.6
0.3
2.5
71.8
300 mA
3.0
3.5
4.0
4.5
5.0
55.0
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Figure 10.
Figure 11.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 3.6V, Flash LEDs are OSRAM LW C9SP, White LEDs OSRAM LWQ38, COUT = 10 µF, CIN = 10 µF, L = Coilcraft
LPS3015–222MLB, TA = +25°C unless otherwise specified.
2.3
Flash LED Current
vs
VIN (Dual Flash LED)
Flash LED current
vs
VIN
0.7
600 mA
600 mA
2.0
450 mA
1.6
FLASH LED CURRENT (A)
INPUT CURRENT (A)
525 mA
0.6
525 mA
300 mA
1.3
0.9
450 mA
0.4
300 mA
0.3
150 mA
0.1
75 mA
0.6
2.5
•
•
•
•
•
3.0
3.5
4.0
4.5
0.0
2.5
5.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
Figure 12.
Figure 13.
Startup into Flash Mode
Single LED
IFLASH = 1.2A
Startup into Torch Mode
Single LED, Hardware Torch Mode, 93.75 mA Torch Setting
ITORCH = 180 mA
Channel1: VOUT (2V/div)
Channel4: ILED (500mA/div)
Channel2: IL (500 mA/div)
Channel3: STROBE (5V/div)
Time Base: 100 µs/div
•
•
•
•
•
Channel1: VOUT (2V/div)
Channel4: IL (100 mA/div)
Channel2: IL (500 mA/div)
Channel3: TX1 (5V/div)
Time Base: 100 µs/div
Figure 14.
10
3.0
INPUT VOLTAGE (V)
Figure 15.
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FUNCTIONAL DESCRIPTION
OVERVIEW
The LM8502 is a 12-LED output driver with a 1.2A synchronous boost converter. Two of the LED outputs are for
driving flash LEDs or a haptic vibra motor; 10 current sinks are for general illumination. The device incorporates
a 2MHz constant frequency, synchronous, current-mode PWM boost converter.
Pins related to Boost Converter:
• Drain connection for internal NMOS and synchronous PMOS switches, SW pins (A4 and B4)
• Converter Output, OUT pins (A3 and B3)
Pins related to Flash:
• High-side current outputs for Flash LEDs, FLASH1 and FLASH2(A1 and A2), each capable of sourcing up to
600 mA current. If not used for flash, can be used to drive, for example, a vibra motor.
• Active high hardware flash enable STROBE (C4). When set to high turns on the flash pulse. Connect to
ground if not used.
• Configurable pin PWM/ENVM/TX2 (D4) can be configured as an active high-voltage-mode enable (ENVM) or
as a dual-polarity power-amplifier synchronization input (TX2). Polarity of TX input can be changed with a
register bit, and when it occurs, it forces Flash into Torch or Flash LED shutdown. Third function for this pin is
PWM input enabling Dynamic Backlight Control. When PWM input is used, ENVM or TX2 cannot be used.
Connect to ground if not used.
• Configurable pin TX1/TORCH (D5) can be configured as an RF power amplifier synchronization input of
hardware torch enable. At TX1 event the Flash LEDs are forced to Torch mode. In Torch mode, when pin is
set high, Flash LEDs are set to Torch current level. Connect to ground if not used.
• Configurable pin LEDI/NTC (C3) can be configured as a high-side current source for indicator LED or
threshold detector for flash LED temperature sensing. Indicator LED has four current levels and can be used,
for example, as flash event indicator. When configured as NTC, the thermistor senses temperature near flash
LEDs; when event occurs, according to a bit setting, flash LEDs are set to either to Torch mode or to
shutdown.
Pins related to LED controlling
• LED output pins D1 to D9 (F1 = Output 1, F2 = Output 2, E1 = Output 3, E2 = Output 4, D1 = Output 5, D2 =
Output 6, C1 = Output 7, C2 = Output 8 and B1 = Output 9). The urrent of these current sinks can be
programmed through the registers with full-scale current setting and current level. They also can be freely
grouped into one of three group faders and be controlled with a single register write. Also incorporated
lighting engines can control these current sinks.
• LED output pin D10/ALS2 (B2 = Output 10) is basically same kind of current sink as all others with one
exception: it can also be configured as Ambient Light Sensing input.
• Note that all LED outputs can each be freely powered either from VOUT (Converter Output) or external voltage
supply.
• TRIG pin (F3) is related to lighting engines. It is used as an external trigger to and from lighting engines.
Other pins
• VIBRAP and VIBRAN pins (A1 and A2) are optional with Flash outputs. They can be used for controlling, for
example, a vibra motor from a register or from lighting engines. When not used in haptic applications, thet
can be used for Flash applications.
• VIN (C5) is the input voltage pin for the device. Voltage range is from 2.7 V to 5.5V.
• ALS1 (D3) is primary Ambient Light Sensing input.
• INT (E3) is interrupt for the micro-controller. Interrupts can come from lighting engine,s as well as from NTC
and from ALS zone change.
• CLK (E4) is an external 32 kHz clock input which enables powerful Power-save mode when device is in idle
state.
• EN (E5) is the enable or reset pin for the device.
• SCL (F4) and SDA (F5) are the I2C-compatible interface clock input and data input/output.
• GND pins (A5 and B5) are for grounding the device.
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MODES OF OPERATION
RESET: In the Reset mode all the internal registers are reset to the default values, and the device goes to
Standby mode after reset. CHIP_EN control bit is low after reset by default. Reset mode is entered always
if the Reset register is written or internal Power-On Reset is active. the LM8502 can be reset by writing
any data to the Reset register (address 3DH). Power-On Reset (POR) will activate during the device
startup or when the supply voltage VIN falls below 1.5V. Once VIN rises above 1.5V, POR will inactivate,
and the device will continue to the Standby mode.
STANDBY: The Standby mode is entered if POR is inactive. In this mode all circuit functions are disabled. Most
of the registers can be written in this mode, and the control bits are effective immediately after startup.
STARTUP: When EN pin is set to '1' the LM8502 initializes EPROM and SRAM memories. Setting the CHIP_EN
bit to '1' causes the INTERNAL STARTUP SEQUENCE to power up all the needed internal blocks. If the
device temperature rises too high, the Thermal Shutdown (TSD) disables the device operation, and
Startup mode is entered until no thermal shutdown is present.
BOOST STARTUP: Soft start for boost is generated in the Boost Startup mode. Boost Startup is entered from
INTERNAL STARTUP SEQUENCE if the EN_BOOST bit is set to '1', or from Normal mode when the
EN_BOOST bit is set to '1'. During Boost Startup all LED outputs are off to ensure smooth startup.
NORMAL: During Normal mode the user controls the device using the Control registers. The registers can be
written in any sequence, and any number of bits can be altered in a register with one write.
POWER-SAVE: Power-save mode is entered when the POWERSAVE_EN bit in Register 36H is set to '1'. This
enables a mode where almost all analog blocks are shut down, when the device is idle.
RESET (POR=1)
POR=0
STANDBY
EN = 1 AND CHIP_EN = 1
Register Reset or POR=1
INTERNAL STARTUP
SEQUENCE
EN = 0 OR CHIP_EN = 0
TSHD = 1
EN_BOOST = 1
EN_BOOST = 0
BOOST STARTUP
EN_BOOST = 1
Boost Voltage > 2.2V
NORMAL MODE
Device not idle
POWERSAVE_EN = 1
and Device is idle
POWERSAVE MODE
Figure 16. Startup Sequence
12
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LED DRIVER
Overview
The LM8502 has 10 current-sink-type LED outputs. The LED outputs can be controlled in three ways described
later on. Each LED output can be powered either from VOUT or from an external voltage supply. The selection of
LED output powering can be done from LED control registers (06H to 0FH) with the LEDx_BAT_CON bit. When
the LEDx_BAT_CON bit is set to '0', LED output is powered from VOUT. Note that changing LED powering does
not enable boost converter automatically. Please also Note that LED output 10 can be configured as an Ambient
Light Sensing (ALS) input; the LED output will not turn on when configured as an ALS input.
Table 1. Full-Scale Current
FSC Bit [1:0]
Max LED (mA)
Current step size, linear scale (µA)
00
3
11.7
01
6
23.5
10
12.5
50
11
25.5
95
Table 2. Current Control When Full-Scale Current Set to 25.5 mA
CURRENT bits
Output Current
0000 0000
0.0 mA
0000 0001
0.1 mA
0000 0010
0.2 mA
.... . .
.... . .
10101111
17.5 mA
...
...
11 111 111
25.5 mA
The Brightness Control register (BRGT) is an 8-bit register that programs the 255 different LED current levels.
The code written to BRGT is translated into an LED current as a percentage of ILED_FULLSCALE as set via the
full-scale current bits (LED control registers bits [4:3]). There are two selectable LED current profiles. Setting LED
control register bit 5 to '1' selects the logarithmic LED current response; setting this bit to '0' selects the linear
weighted curve. With the maximum full-scale current and logarithmic setting one can achieve up to 4000:1
dimming ratio with maximum full-scale setting at the first steps of logarithmic curve (6.25 µA/25.5 mA = 1/4080).
Current steps are displayed in Table 2 for linear scale. With a logarithmic setting the step size varies, but is at
minimum 0.78 µA when full-scale control is 00, and 6.25 µA when full-scale control is 11.
For LED dimming a logarithmic or linear scale can be applied — see the figure Figure 17. A logarithmic or linear
scheme can be set for both the program execution engine control and direct brightness control. By using a
logarithmic brightness scale the visual effect looks like linear to the human eye. The logarithmic brightness scale
is created with technique, which has internal resolution of 12 bits. (8-bit control can be seen by user.)
26.0
26
25.5 mA
25.5 mA
20.8
20.8
CURRENT (mA)
CURRENT (mA)
12.5 mA
6 mA
15.6
3 mA
10.4
12.5 mA
15.6
3 mA
10.4
6 mA
5.2
5.2
0
0
52
104
156
208
260
0
0
CURRENT REGISTER CODE (dec)
52
104
156
208
CURRENT REGISTER CODE (dec)
Figure 17. LED Dimming In Linear and Logarithmic Modes
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Controlling Brightness of LED Outputs
1. Direct Brightness Control
– All LM8502 LED drivers, D1 to D10, can be controlled independently through the two-wire serial I2Ccompatible interface. For each high-side driver there is a current control register.
2. Controlling by Program Execution Engines
– Engine control is used when the user wants to create programmed sequences. The program execution
engine has higher priority than direct control registers. Therefore, if the user has set a certain value to the
current register, it will be automatically overridden when the program execution engine controls the driver.
LED control and program execution engine operation are described later on.
3. Group Fader Control
– In addition to LED-by-LED current register control, the LM8502 is equipped with group fader control which
allows the user to fade in or fade out multiple LEDs by writing to only one register. This is a useful
function to minimize serial bus traffic between the MCU and the LM8502. The LM8502 has three group
fader registers, thus, it is possible to form three fader groups. Fade-in and fade-out times can also be set
with the device. These times control the time when ramping up or down the group current value. Time
can be set with 4 bits according to the following table:
Table 3. Fade in/out times
FADE IN/FADE OUT
Time, s
0000
0.0
0001
0.05
0010
0.1
0011
0.2
0100
0.3
0101
0.4
0110
0.5
0111
0.6
1000
0.7
1001
0.8
1010
0.9
1011
1.0
1100
1.5
1101
2.0
1110
3.0
1111
4.0
– When the LM8502 is shut down (through chip_en), the fading off may be achieved. When the “fade-to-off”
bit is set to 1, the group fade times have effect, and the LEDs fade off according to the time set in the
register. Note that Ambient Light Sensing and PWM input are also set through these group fader controls.
LM8502 ENGINE PROGRAMMING
The LM8502 has two independent programmable lighting engines. Both lighting engines have their own program
memory block allocated by the user. Note that in order to access program memory the operation mode needs to
be LOAD Program, at least for one of the lighting engines. Please also note also that one should not change
from RUN mode directly to LOAD program. Correct sequence would be RUN (10) –> DISABLED (00) –> LOAD
(01). Program execution is clocked with 32 768 Hz clock. This clock can be generated internally or by using an
external 32 kHz clock that can be connected to CLK pin. Use of an external clock enables synchronization of
LED timing to this clock rather than to the internal clock. Note that the last instruction in the memory should be
END or GO_TO_START.
The engines have different priorities; when more than one engine is controlling the same LED output, LED
engine 1 has the higher priority than LED engine 2. Supported instruction set is listed in the tables below:
14
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Table 4. LM8502 LED Driver Instructions
Bit
[15]
Bit
[14]
Bit
[13]
Bit
[12]
Ramp
0
prescale
Fast Ramp
1
1
0
0
Set Brightness
(Absolute value)
0
1
0
Set Brightness
(Relative value)
0
0
0
Wait
0
prescale
Inst.
Bit
[11]
Bit
[10]
Bit
[9]
Bit
[8]
0
1
0
Sign
0
0
0
0
0
Brightness value
0
0
0
0
Sign
Brightness value
step time
Bit
[7]
Bit
[6]
Bit
[5]
Bit
[4]
Sign
Time
Bit
[3]
Bit
[2]
Bit
[1]
Bit
[0]
# of increments
Step size
0
0
# of increments
0
0
0
0
0
0
0
Bit
[3]
Bit
[2]
Bit
[1]
Bit
[0]
Table 5. LM8502 LED Driver Instructions with Variables
Bit
[15]
Bit
[14]
Bit
[13]
Bit
[12]
Bit
[11]
Bit
[10]
Bit
[9]
Bit
[8]
Bit
[7]
Bit
[6]
Bit
[5]
Bit
[4]
Variable Ramp
1
0
0
0
0
1
0
0
0
0
prescale
sign
Variable Set
Brightness
1
0
0
0
0
1
0
0
0
1
1
Inst.
step time
# of
increments
0
0
0
brightness
value
Bit
[4]
Bit
[3]
Bit
[2]
Table 6. LM8502 LED Mapping Instructions
Bit
[15]
Bit
[14]
Bit
[13]
Bit
[12]
Bit
[11]
Bit
[10]
Bit
[9]
Bit
[8]
Bit
[7]
mux_ld_start
1
0
0
1
1
1
0
0
0
SRAM address 0 – 47
mux_ld_end
1
0
0
1
1
1
0
0
1
SRAM address 0 – 47
mux_sel
1
0
0
1
1
1
0
1
0
mux_clr
1
0
0
1
1
1
0
1
0
0
0
0
0
mux_inc
1
0
0
1
1
1
0
1
1
0
0
0
0
mux_dec
1
0
0
1
1
1
0
1
1
1
0
0
0
mux_set
1
0
0
1
1
1
1
1
1
Inst.
Bit
[6]
Bit
[5]
Bit
[1]
Bit
[0]
0
0
0
0
0
0
0
0
0
LED/haptic select
SRAM address 0 – 47
Table 7. LM8502 BRANCH Instructions
Bit
[15]
Bit
[14]
Bit
[13]
Bit
[12]
Bit
[11]
Go to Start
0
0
0
0
0
Branch
1
0
1
Int
1
1
0
0
0
1
0
0
0
0
0
0
0
0
0
0
End
1
1
0
Int
Reset
0
X
X
X
X
X
X
X
X
X
X
Trigger
1
1
1
ENGI
NE2
ENGI
NE1
ENG
INE1
X
Bit
[1]
Bit [0]
Inst.
Bit
[10]
Bit
[9]
Bit
[8]
Bit
[7]
Bit
[6]
Bit
[5]
Bit
[4]
0
0
0
0
0
0
0
Loop count
X
X
X
Bit
[2]
Bit
[1]
Bit
[0]
0
0
0
0
Step number
Wait for a trigger
Ext. trig
Bit
[3]
Send a trigger
Ext. trig
X
X
ENGI
NE2
X
Table 8. LM8502 Variable Branch Instruction and Conditional Instructions
Inst.
Variable Branch
Bit
[15]
Bit
[14]
Bit
[13]
Bit
[12]
Bit
[11]
Bit
[10]
Bit
[9]
1
0
0
0
0
1
1
Bit
[8]
Bit
[7]
Bit
[6]
Bit
[5]
Bit
[4]
Bit
[3]
Bit
[2]
step number
loop count
jne (jump if not equal)
1
0
0
0
1
0
0
Number of instructions to be skipped if
the operation returns true
jl (jump if less)
1
0
0
0
1
0
1
Number of instructions to be skipped if
the operation returns true
variable 1
variable 2
jge (jump if greater
than)
1
0
0
0
1
1
0
Number of instructions to be skipped if
the operation returns true
variable 1
variable 2
je (jump if equal)
1
0
0
0
1
1
1
Number of instructions to be skipped if
the operation returns true
variable 1
variable 2
variable 1
variable 2
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Table 9. Data Transfer and Arithmetic Instructions
Bit
[15]
Bit
[14]
Bit
[13]
Bit
[12]
ld
1
0
0
1
add
1
0
0
1
sub
1
0
0
1
Inst.
Bit
[15]
Bit
[14]
Bit
[13]
Bit
[12]
Variable add
1
0
0
1
Variable sub
1
0
0
1
Inst.
Bit
[11]
Bit
[10]
Bit
[9]
Bit
[8]
Bit
[7]
Bit
[6]
Bit
[5]
Bit
[4]
Bit
[3]
target variable
0
0
8-bit value
target variable
0
1
8-bit value
target variable
1
0
8-bit value
Bit
[2]
Bit
[1]
Bit
[0]
Bit
[2]
Bit
[1]
Bit
[0]
Table 10. Arithmetic Instructions with Variables
Bit
[11]
Bit
[10]
Bit
[9]
Bit
[8]
Bit
[7]
Bit
[6]
Bit
[5]
Bit
[4]
Bit
[3]
target variable
1
1
0
0
0
0
variable 1
variable 2
target variable
1
1
0
0
0
1
variable 1
variable 2
RAMP INSTRUCTIONS
RAMP Instruction
This instruction is useful for smoothly changing from one brightness value into another on the D1 to D10 outputs,
in other words generating ramps (with a negative or positive slope). The LM8502 allows programming of very fast
and very slow ramps.
Ramp instruction generates a brightness ramp, using the effective brightness value as a starting value. At each
ramp step the output is incremented/decremented by one unit, unless the step time span is 0 or incremental
value is 0. Time span for one ramp step is defined with prescale-bit [14] and step time-bits [13:9]. Prescale = 0
sets 0.49 ms cycle time, and prescale = 1 sets 15.6 ms cycle time, so the minimum time span for one step is
0.49 ms (prescale * step time span = 0.49ms x 1); the maximum time span is 15.6 ms x 31 = 484ms/step.
If all the step time bits [13:9] are set to zero, depending on the prescale instruction works as absolute or relative
set_brightness instruction. If prescale is set to '0' (Set Brightness Relative value), all the mapped LED outputs
are increased or decreased (depending on the sign bit) with a value defined by # of increments in 0.49 ms. With
relative value the sign defines whether the BRGT value is decremented or incremented If the prescale is set to '1'
(Set Brightness Absolute value), all the mapped LED outputs are set to same current level defined by # of
increments in 0.49 ms regardless of the effective brightness level.
The incremental value defines how many steps will be taken during one ramp instruction — increment maximum
value is 255d, which equals incrementing from zero value to the maximum value. If brightness reaches
minimum/maximum value (0/255) during the ramp instruction, the ramp instruction will be executed to the end
regardless of saturation. This enables ramp instruction to be used as a combined ramp & wait instruction. Note:
Ramp instruction is the wait instruction when the increment bits [7:0] are set to zero. Setting bit LOG_EN
high/low sets logarithmic (1) or linear ramp (0). By using the logarithmic ramp setting the visual effect appears
like a linear ramp, because the human eye behaves in a logarithmic way.
Table 11. RAMP
Name
Value (d)
0
Divides master clock (32.768 Hz) by 16 =
2048 Hz resulting 0.488 ms cycle time
1
Divides master clock (32.768 Hz) by 512 =
64 Hz resulting 15.625 ms cycle time
0
Increase brightness output
1
Decrease brightness output
prescale
sign
Description
step time
0 - 31
One ramp increment done in (step time) x
(prescale).
# of increments
0 - 255
The number of increment/decrement cycles
Note: Value 0 takes the same time as
increment
16
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FAST RAMP Instruction
The fast ramp instruction generates a brightness ramp, using the effective brightness value as a starting value.
At each ramp step the output is incremented/decremented by step size. Time span for one ramp step is always
0.49 ms. The time span for the whole ramp is determined by the number of increments. For example if step size
is 4 and the number of increments is 40, the whole ramp time span is 40*0.49 ms = 19.6 ms. For every 0.49 ms
mapped, output brightnesses are incremented by 4, so full ramp increments the mapped output values by 40*4 =
160.
Table 12. FAST RAMP
sign
step size
0
Increase brightness output
1
Decrease brightness output
0–3
(0=2, 1=4, 2=8, 3=16)
Value indicating how much the brightness is
incremented in 0.49 ms
1–63
The number of increment/decrement cycles
# of increments
RAMP Instruction with Variables
Programming ramps with variables is very similar to programming ramps with numerical operands. The only
difference is that when the instruction is starated, the step time and number of increments are captured from
variable registers. If the variables are updated after starting the instruction execution, it will have no effect on
instruction execution. Again, at each ramp step the mapped outputs are incremented/decremented by one unless
step time is 0 or increment is 0. Time span for one step is defined with prescale and step time bits. Step time is
defined with variables A, B, C or D. Variables A, B and C are set with LED instruction. Variable D is a global
variable and can be set by writing the I2C Variable register 3CH. General purpose ADC result can be used as a
source for variable D as well. Note that FAST RAMP instruction cannot use variables.
Table 13. RAMP with Variable
Name
Value (d)
Description
step time
0–3
0 = local variable A
1 = local variable B
2 = global variable C
2
3 = I C variable register value or general purpose ADC value, variable
D
One ramp increment done in (step time) x
(prescale). Step time is loaded with the value
of the variable. The value of the variable
should be from 0–31 for correct operation
# of increments
0–3
0 = local variable A
1 = local variable B
The number of increment/decrement cycles.
2 = global variable C
Value is taken from variable.
3 = I2C variable register value or general purpose ADC value, variable
D
LED MAPPING INSTRUCTIONS
These commands define the engine-to-LED mapping. The mapping information is stored in a table, which is
stored in the SRAM (program memory of the LM8502). Location of the mapping table can exist anywhere in
SRAM. LM8502 has two lighting engines (Engines) which can be mapped to 10 LED drivers or haptic driver
freely. Each mapping takes one 16-bit instruction and a mapping table consists of multiple mappings. The
engines can use the same mapping table or have their own mapping table. Each of the LED outputs or haptic
output is mapped by following manner (note that this is also the way they are written into the SRAM memory):
These commands define the engine-to-LED mapping. The mapping information is stored in a table, which is
stored in the SRAM (program memory of the LM8502). Location of the mapping table can exist anywhere in
SRAM. LM8502 has two lighting engines (Engines) which can be mapped to 10 LED drivers or haptic driver
freely. Each mapping takes one 16–bit instruction and a mapping table consists of multiple mappings. The
engines can use the same mapping table or have their own mapping table. Each of the LED outputs or haptic
output is mapped by following manner (note that this is also the way they are written into the SRAM memory):
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Table 14. LED Mapping
Output
Value (dec) / (binary)
LED1
1 / 0000 0000 0000 0001
LED2
2 / 0000 0000 0000 0010
LED3
4 / 0000 0000 0000 0100
LED4
8 / 0000 0000 0000 1000
LED5
16 / 0000 0000 0001 0000
LED6
32 / 0000 0000 0010 0000
LED7
64 / 0000 0000 0100 0000
LED8
128 / 0000 0000 1000 0000
LED9
256 / 0000 0001 0000 0000
LED10
512 / 0000 0010 0000 0000
Haptic
1024 / 0000 0100 0000 0000
One mapping can control one or multiple LED outputs or haptic. In a case where multiple LED outputs or LED
outputs and haptic are mapped, one sets to '1' the applicable 'LED/haptic bit'. For example:
Table 15. Mapping Example
Mapped Outputs
Value (dec) / (binary)
LED1, LED3 and LED9
261 / 0000 0001 0000 0101
LED2, LED4, LED6, LED8, LED10 and haptic
1706 / 0000 0110 1010 1010
There are totally seven commands for the engine-to-LED driver control: mux_ld_start, mux_ld_end, mux_sel,
mux_clr, mux_inc, mux_dec, mux_set. Note that the LED mapping instructions do not update brightness values
to LED outputs. Brightness values are updated after ramp or set_brgt instructions.
MUX_LD_START; MUX_LD_END Instructions
Mux_ld_start and mux_ld_ end define the mapping table location in the memory. Mux_ld_start defines the start
address, and mux_ld_end indicates the end address of the mapping table.
MUX_SEL Instruction
With a mux_sel instruction one, and only one, LED driver can be connected to a lighting engine. Connecting
multiple LEDs to one engine is done with the mapping table. After the mapping has been released from an LED,
the brightness register value will still control the LED brightness.
Table 16. MUX_SEL
Name
Value (d)
LED select
18
0 - 16
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Description
0 = no drivers selected
1 = LED1 selected
2 = LED2 selected
...
9 = LED9 selected
10 = LED10 selected
11 = haptic
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MUX_CLR Instruction
Mux_clr clears engine-to-driver mapping. After the mapping has been released from an LED, the Brightness
register value will still control the LED brightness.
MUX_INC Instruction
Mux_inc instruction sets the next row active in the mapping table each time it is called. For example, if the 2nd
row is active after a mux_inc instruction call, the 3rd row will be active. If the mapping table end is reached,
activation will roll to the mapping table start address the next time the mux_inc instruction is called. The engine
will not push a new brightness value to the LED driver output before a SET_BRGT or RAMP instruction is
executed. If the mapping has been released from an LED, the value in the Brightness register will still control the
LED brightness.
MUX_DEC Instruction
Mux_dec instruction sets the previous row active in the mapping table each time it is called. For example, if the
3rd row is active, after mux_dec instruction call the 2nd row will be active. If the mapping table start address is
reached, activation will roll to the mapping table end address the next time the mux_dec instruction is called. The
engine will not push a new brightness value to the LED driver output before a SET_BRGT or RAMP instruction is
executed. If the mapping has been released from an LED, the value in the Brightness register will still control the
LED brightness.
MUX_SET Instruction
Mux_set sets the index pointer to point to the mapping table row defined by bits [6:0] and sets the row active.
The engine will not push a new brightness value to the LED driver output before SET_BRGT or RAMP instruction
is executed. If the mapping has been released from an LED, the value in the Brightness register will still control
the LED brightness.
SET BRIGHTNESS INSTRUCTIONS
SET BRIGHTNESS Instruction
This instruction is used for setting the brightness value on the outputs D1 to D10 and haptic without any ramps.
Set BRGT output value from 0 to 255 with BRGT value bits [7:0]. Instruction execution takes sixteen 32 kHz
clock cycles (=488 μs). Setting the brightness can be relative or absolute depending on bit [14]. If bit is set to '0'
(Set Brightness Relative value), all the mapped LED outputs are increased or decreased (depending on the sign
bit) with a value defined by the BRGT value in 0.49 ms. With relative value bit [8] defines whether the BRGT
value is decremented or incremented. If the prescale is set to '1' (Set Brightness Absolute value), all the mapped
LED outputs are set to the same current level defined by the BRGT value in 0.49 ms regardless of the effective
brightness level.
Table 17. SET BRIGHTNESS
Name
Setting type
Sign (only for relative setting)
BRGT value
Value (d)
0–1
0 = relative setting
1 = absolute setting
0–1
0 = increase brightness
1= decrease brightness
0–255
Description
Defines how the brightness of mapped LED
or haptic outputs is set
Defines whether the brightness value is
increased or decreased with the BRGT value
BRGT output value 0 100%
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SET BRIGHTNESS with Variable Instruction
Table 18. SET BRIGHTNESS with Variable
Name
Variable
Value (d)
Description
0 = local variable A
1 = local variable B
2 = global variable C
3 = I2C variable register value or general
purpose ADC value, variable D
0–3
WAIT INSTRUCTION
When a wait instruction is executed, the engine is set in a wait status, and the brightness values on the outputs
are frozen.
Table 19. WAIT
Name
Value (d)
Description
0
Divide master clock (32.768 Hz) by 16 which
means 0.488 ms cycle time
1
Divide master clock (32 768 Hz) by 512 which
means 15.625 ms cycle time
prescale
time
Total wait time will be = (time) x (prescale).
Maximum 484 ms, minimum 0.488 ms
1– 31
LED MAPPING INSTRUCTIONS
These commands define the engine-to-LED mapping. The mapping information is stored in a table, which is
stored in the SRAM (program memory of the LM8502). Location of the mapping table can exist anywhere in
SRAM. LM8502 has two lighting engines (Engines) which can be mapped to 10 LED drivers or haptic driver
freely. Each mapping takes one 16-bit instruction and a mapping table consists of multiple mappings. The
engines can use the same mapping table or have their own mapping table. Each of the LED outputs or haptic
output is mapped by following manner (note that this is also the way they are written into the SRAM memory):
These commands define the engine-to-LED mapping. The mapping information is stored in a table, which is
stored in the SRAM (program memory of the LM8502). Location of the mapping table can exist anywhere in
SRAM. LM8502 has two lighting engines (Engines) which can be mapped to 10 LED drivers or haptic driver
freely. Each mapping takes one 16–bit instruction and a mapping table consists of multiple mappings. The
engines can use the same mapping table or have their own mapping table. Each of the LED outputs or haptic
output is mapped by following manner (note that this is also the way they are written into the SRAM memory):
Table 20. LED Mapping
Output
Value (dec) / (binary)
LED1
1 / 0000 0000 0000 0001
LED2
2 / 0000 0000 0000 0010
LED3
4 / 0000 0000 0000 0100
LED4
8 / 0000 0000 0000 1000
LED5
16 / 0000 0000 0001 0000
LED6
32 / 0000 0000 0010 0000
LED7
64 / 0000 0000 0100 0000
LED8
128 / 0000 0000 1000 0000
LED9
256 / 0000 0001 0000 0000
LED10
512 / 0000 0010 0000 0000
Haptic
1024 / 0000 0100 0000 0000
20
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One mapping can control one or multiple LED outputs or haptic. In a case where multiple LED outputs or LED
outputs and haptic are mapped, one sets to '1' the applicable 'LED/haptic bit'. For example:
Table 21. Mapping Example
Mapped Outputs
Value (dec) / (binary)
LED1, LED3 and LED9
261 / 0000 0001 0000 0101
LED2, LED4, LED6, LED8, LED10 and haptic
1706 / 0000 0110 1010 1010
There are totally seven commands for the engine-to-LED driver control: mux_ld_start, mux_ld_end, mux_sel,
mux_clr, mux_inc, mux_dec, mux_set. Note that the LED mapping instructions do not update brightness values
to LED outputs. Brightness values are updated after ramp or set_brgt instructions.
MUX_LD_START; MUX_LD_END Instructions
Mux_ld_start and mux_ld_ end define the mapping table location in the memory. Mux_ld_start defines the start
address, and mux_ld_end indicates the end address of the mapping table.
MUX_SEL Instruction
With a mux_sel instruction one, and only one, LED driver can be connected to a lighting engine. Connecting
multiple LEDs to one engine is done with the mapping table. After the mapping has been released from an LED,
the Brightness register value will still control the LED brightness.
Table 22. MUX_SEL
Name
LED select
Value (d)
0 - 16
Description
0 = no drivers selected
1 = LED1 selected
2 = LED2 selected
...
9 = LED9 selected
10 = LED10 selected
11 = haptic
MUX_CLR Instruction
Mux_clr clears engine-to-driver mapping. After the mapping has been released from an LED, the Brightness
register value will still control the LED brightness.
MUX_INC Instruction
Mux_inc instruction sets the next row active in the mapping table each time it is called. For example, if the 2nd
row is active after a mux_inc instruction call, the 3rd row will be active. If the mapping table end is reached,
activation will roll to the mapping table start address the next time the mux_inc instruction is called. The engine
will not push a new brightness value to the LED driver output before a SET_BRGT or RAMP instruction is
executed. If the mapping has been released from an LED, the value in the Brightness register will still control the
LED brightness.
MUX_DEC Instruction
Mux_dec instruction sets the previous row active in the mapping table each time it is called. For example, if the
3rd row is active, after mux_dec instruction call the 2nd row will be active. If the mapping table start address is
reached, activation will roll to the mapping table end address the next time the mux_dec instruction is called. The
engine will not push a new brightness value to the LED driver output before a SET_BRGT or RAMP instruction is
executed. If the mapping has been released from an LED, the value in the Brightness register will still control the
LED brightness.
MUX_SET Instruction
Mux_set sets the index pointer to point to the mapping table row defined by bits [6:0] and sets the row active.
The engine will not push a new brightness value to the LED driver output before SET_BRGT or RAMP instruction
is executed. If the mapping has been released from an LED, the value in the Brightness register will still control
the LED brightness.
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GO-TO-START INSTRUCTION
Go-to-start command resets the Program Counter register; the program continues executing from the I2C register
program start address. Command takes sixteen 32 kHz clock cycles. Note that default value for all program
memory registers is 00h, which is the “Go-to-Start” command.
BRANCH
BRANCH Instruction
Branch instruction is mainly indented for repeating a portion of the program code several times. Branch
instruction loads step number value to program counter. The loop-count parameter defines how many times the
instructions inside the loop are repeated. The LM8502 supports nested looping, i.e., loop inside loop. The
number of nested loops is not limited. Instruction takes sixteen 32 kHz clock cycles.
Table 23. BRANCH Instruction
Name
Value (d)
Description
loop count
0-63
The number of loops to be done. 0 means an
infinite loop.
step number
0-95
The step number to be loaded to program
counter
BRANCH Instruction with Variable
Table 24. BRANCH Instruction with Variable
Name
step number
Value (d)
Description
0-3
0 = local variable A
1 = local variable B
2 = global variable C
3 = I2C variable register value or general
purpose ADC value, variable D
Selects the variable for step number value.
Step number is loaded with the value of the
variable.
INT INSTRUCTION
Sends interrupt to processor by pulling the INT pin down and setting the corresponding status bit high. Interrupt
can be cleared by reading interrupt bits in STATUS/INTERRUPT register. With this instruction program execution
continues.
END INSTRUCTION
Ends program execution and resets PC. Instruction takes sixteen 32 kHz clock cycles. End instruction can have
two parameters, INT and RESET. These parameters are described in tables below. Execution engine bits are set
to zero, i.e., Hold mode.
Table 25. END Instruction
Name
Value
No interrupt will be sent. PWM registers
values will remain intact. Program counter
value is set to 0.
1
Reset program counter value to 0 and send
interrupt to processor by pulling the INT pin
down and setting corresponding status bit
high to notify that program has ended.
Brightness register values will remain intact.
Interrupt can be cleared by reading interrupt
bits in STATUS/INTERRUPT register
int
22
Description
0
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Table 25. END Instruction (continued)
Name
Value
reset
Description
0
Reset program counter value to 0 and hold.
Brightness register values remain intact.
1
Reset program counter value to 0 and hold.
Brightness register values of the nonmapped drivers will remain. Brightness
register values of the mapped drivers will be
set to '0000 0000'.
TRIGGER INSTRUCTION
Wait or send triggers can be used to, e.g,. synchronize operation between the program execution engines. A
send trigger instruction takes sixteen 32 kHz clock cycles, and a wait for trigger takes at least sixteen 32 kHz
clock cycles. The receiving engine stores the triggers which have been sent. Received triggers are cleared by a
wait-for-trigger instruction. A wait-for-trigger instruction is executed until all the defined triggers have been
received. (Note: several triggers can be defined in the same instruction.) An external trigger input signal must
stay low for at least two 32 kHz clock cycles to be executed. Trigger output signal is three 32 kHz clock cycles
long. External trigger signal is active low, i.e. when trigger is send/received the pin is pulled to GND. Sent
external trigger is masked, i.e., the device which has sent the trigger will not recognize it. If send and wait
external triggers are used on the same instruction, the send external trigger is executed first, then the wait
external trigger.
Table 26. TRIGGER Instruction
Name
wait for a trigger
send a trigger
Value (d)
Description
0 - 31
Wait for a trigger from the engine (s). Several
triggers can be defined in the same
instruction. Bit [7] engages engine 1, bit [8]
engages engine 2, and bit [6] is for external
trigger I/O. Bits [4], [5] and [9] are not in use.
0 - 31
Send a trigger to the engine(s). Several
triggers can be defined in the same
instruction. Bit [1] engages engine 1, bit [2]
engages engine 2, and bit [6] is for external
trigger I/O. Bits [3], [4] and [5] are not in use.
CONDITIONAL INSTRUCTIONS
The LM8502 includes the following conditional jump instructions: jne (jump if not equal), jge (jump if greater or
equal), jl (jump if less) and je (jump if equal). If the condition is true, a certain number of instructions will be
skipped (i.e,. the program jumps forward to a location relative to the present location). If condition is false, then
the next instruction will be executed.
Table 27. Conditional Instruction
Name
Number of instructions to be skipped if the
operation returns true
Value (d)
Description
0–31
The number of instructions to be skipped
when statement is true. Note: value 0 means
redundant code
0–3
0 = local variable A
1 = local variable B
2 = global variable C
3 = I2C variable register value or general
purpose ADC value, variable D
0–3
0 = local variable A
1 = local variable B
2 = global variable C
3 = I2C variable register value or general
purpose ADC value, variable D
variable 1
variable 2
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ARITHMETIC INSTRUCTIONS
LD
This instruction is used to assign a value into a variable; the previous value in that variable is overwritten. Both
engines have two local variables called A and B. The variable C is a global variable for both engines.
Table 28. Assign Value to Variable
Name
target variable
8–bit value
Value (d)
Description
0–2
0 = variable A
1 = variable B
2 = variable C
0–255
Variable value
ADD
Operator either adds 8-bit value to the current value of the target variable, or adds the value of variable 1 (A, B,
C or D) to the value of variable 2 (A, B, C or D) and stores the result in the register of variable A, B or C.
Variables overflow from 255 to 0.
Table 29. ADD with Numerical Operands
Name
Value (d)
target value
0–2
8–bit value
0–255
Description
0 = variable A
1 = variable B
2 = variable C
The value to be added
Table 30. ADD with Variables
Name
target value
variable 1
variable 2
Value (d)
Description
0–2
0 = variable A
1 = variable B
2 = variable C
0–3
0 = local variable A
1 = local variable B
2 = global variable C
3 = I2C variable register value or general
purpose ADC value, variable D
0–3
0 = local variable A
1 = local variable B
2 = global variable C
3 = I2C variable register value or general
purpose ADC value, variable D
SUB
Operator either subtracts 8-bit value to the current value of the target variable, or subtracts the value of variable
1 (A, B, C or D) to the value of variable 2 (A, B, C or D) and stores the result in the register of variable A, B or C.
Variables overflow from 255 to 0.
Table 31. SUB with Numerical Operands
Name
Value (d)
target value
0–2
8–bit value
0–255
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Description
0 = variable A
1 = variable B
2 = variable C
The value to be subtracted
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Table 32. SUB with variables
Name
target value
variable 1
variable 2
Value (d)
Description
0–2
0 = variable A
1 = variable B
2 = variable C
0–3
0 = local variable A
1 = local variable B
2 = global variable C
3 = I2C variable register value or general
purpose ADC value, variable D
0–3
0 = local variable A
1 = local variable B
2 = global variable C
3 = I2C variable register value or general
purpose ADC value, variable D
HAPTIC FEEDBACK
The LM8502 can be set to Haptic Feedback mode, where the FLASH1/VIBRAP and FLASH2/VIBRAN pins can
be used for driving a vibra motor. The device incorporates H-bridge which is controlled with a PWM generator.
The PWM generator can be controlled through writing I2C registers or lighting engines or through grouping haptic
into one of the group faders. PWM frequency can be selected with 2 bits (bits [4:3] in the Haptic Feedback
Control register 21H) in the following manner: 00 = 157 Hz, 01 = 490 Hz, 10 = 980 Hz, 11 = 3.9 kHz. PWM has
8-bit resolution. Different haptic modes can be selected according to Table 34.
These different modes control the direction of vibra motor. The PWM control sets the speed of the motor. See
Figure 18 and Table 33 below.
1. In mode 000 the haptic is disabled.
2. In mode 001 there is PWM on both A and B channels. The frequency of the PWM is double the frequency
set in register 21H Haptic control 2. When the PWM value is 00H the B-channel is fully on, the A-channel is
off, and the motor is running clockwise. Increasing the PWM value increases the A-channel pulse length and
decreases B-channel pulse length. In the middle of the PWM range (value 80H) both channels PWM have
the same pulse length so that the motor is stopped. When the PWM reaches value FFH, the A channel is
fully on, the B channel is off and motor is running counterclockwise.
3. In mode 010 the PWM register controls the A-channel; B-channel is in low state (off) all the time. Increasing
the PWM increases the motor speed. The motor is running counter clockwise.
4. In mode 011 the PWM register controls the B-channel; A-channel is in low state (off) all the time. Increasing
the PWM increases the motor speed. The motor is running clockwise.
5. In mode 100 the haptic is disabled.
6. In mode 101 the PWM is on both channels. The functionality is the same as in mode 001 with one exception.
In the middle PWM value (80H) there is no activity on either of the channels. This is to save power in the
middle value.
7. In mode 110 the PWM register controls the A-channel; B-channel is in high state (on) all the time. With PWM
value 00H the motor is running at full speed. Increasing the PWM value reduces the motor speed. Motor is
running clockwise.
8. In mode 111 the PWM register controls the B-channel; A-channel is in high state (on) all the time. With PWM
value 00H the motor is running at full speed. Increasing the PWM reduces the motor speed. Motor is running
counter-clockwise.
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VOUT
A-channel
B-channel
Motor
Figure 18.
Table 33. H-Bridge Truth Table
PFET Left A-channel
NFET Left A-channel
PFET Right B-channel
N-fet Right B-channel
Operation of the motor
On
Off
Off
On
Motor goes Clockwise
Off
On
On
Off
Motor goes Counter-Clockwise
On
Off
On
Off
Motor 'brakes'
Off
On
Off
On
Motor 'brakes'
Table 34. Haptic Modes
HAPT_SEL_MODE[2:0]
Description
000
Haptic disabled
001
PWM to both channels (2*pwm_freq)
010
PWM on A channel, B channel in low state
011
PWM on B channel, A channel in low state
100
Haptic disabled
101
PWM to both channels, no activity at center value (2*pwm_freq)
110
PWM on A channel, B channel in high state
111
PWM on B channel, A channel in high state
Haptic can be controlled with the lighting engines also. Haptic is mapped to the engines like LED outputs with
mapping tables of with mux_sel instruction. All the instructions work the same with haptic as with the LED
outputs. One must take into account which haptic mode is selected, since the haptic mode cannot be changed
with the engines, but only from registers with I2C.
Haptic can be used also instead of the PWM input. This enables, for example, the use of lighting engines with
ALS or PWM control directly from register. Haptic is selected instead of PWM input by setting bit [1] in register
36H PWM_INPUT_SEL to '0'. When in Haptic mode there is a one-second wait before going to Power-save
mode. This allows the vibra motor to stop without causing any issues to the LM8502.
During haptic operation boost is set to Constant Voltage mode (selectable 4.5V or 5.0V).
26
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Haptic feedback control
register
Vboost
Haptic PWM duty cycle
register
pwm_p
Haptic PWM
generator
Trig
Channel A
H-Bridge
pwm_n
Channel B
Vibra
Motor
Clk_2 MHz
Engine controlling
PWM duty cycle
AMBIENT LIGHT SENSING
The LM8502 incorporates an Ambient Light Sensing (ALS) input interface which translates an analog output of
ambient light sensor, to a user specified brightness level. In LM8502 there are two ALS inputs. One is dedicated
solely to ambient light sensing (ALS1), the other is multiplexed with LED output 10 (ALS2). Note that when ALS2
is in use LED output D10 cannot be enabled. If the two ALS inputs are selected, the ALS input functionality can
be defined with two bits in ALS Control register 11H as described in Table 35.
Group Fader Registers
(48H, 49H and 4AH)
Ambient Light
Sensing and
Targer Light
Calculation
Target Light
Ambient Light
Calculation
Ambient Light
Calculation
Result
Dynamic
Backlight
Control
LED Mapping
PWM INPUT (pin)
Engine Control (via Haptic)
Figure 19. Ambient Light Sensing
Table 35. Ambient Light Sensor Input Functionality
ALS_SEL[1:0]
Function
00
The lowest of ALS1 or ALS2 is the ambient light sensor input
01
ALS1 is the ambient light sensor input
10
ALS2 is the ambient light sensor input
11
The highest of ALS1 or ALS2 is the ambient light sensor input
ALS is designed so that it controls the LED outputs through the group controls. LED outputs, which should be
controlled by the ambient light sensing, need to be grouped into one of the three groups. There is an enable for
each group that selects whether the ALS affects a certain group or not. For example, one group of LED outputs
may be controlled by ALS along, another by ALS and PWM, and the third group may be controlled only from the
Group Fader register (ALS or PWM having no effect on this group).
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Each group fader register value scales the ALS input. This enables different brightness levels for different
groups. After ALS input is multiplied with group scaling it is multiplied with PWM control (if the PWM is selected
for the group). The control for PWM can come from the external PWM input pin or from the lighting engines.
When PWM control comes from the lighting engines, the Haptic outputs cannot be used. After ALS input is
multiplied with PWM control it is mapped into LED outputs. (See the ALS sensing flow in Figure 22.) The Ramp
control manages LED current-level transitions from one desired brightness code to the next, as described in the
section regarding Group Fader Control.
Table 36. Ambient Light Truth Table: How ALS and PWM Enables Affect Group of LED Outputs
Grouping
ALS_en
PWM_en
no
works only when LED
outputs grouped
works only when LED
outputs grouped
Current value mapped to LED outputs
yes
no
no
Group current control
yes
yes
no
Group current x ALS
yes
no
yes
Group current x PWM
yes
yes
yes
Group current x ALS x PWM
LED outputs controlled through register or lighting
engine
ALS is controlled with the ALS_en_G1, ALS_en_G2 and ALS_en_G3 bits. Setting one of these bits to ‘1’ turns
on the ALS circuitry.
The LM8502 incorporates internal resistors for scaling ambient light sensor currents. This enables the use of
different sensors and also the high impedance state when device is in standby, which saves energy. Note that
the internal resistor value is the same for both of the ambient light inputs, which means that when using both
ALS inputs sensors must be the same. Use of an external resistor is also possible. When an external resistor is
used the en_ext_res bit should be set to ‘1’. When en_ext_res is set to ‘0’, the internal resistor is selected with
the als_res_sel[1:0] bits. see Table 37.
Table 37. Ambient Light Resistor Selection
EN_EXT_RES
ALS_RES_SEL[1:0]
Resistor value (kOhm)
0
00
1.25
0
01
2.5
0
10
5
0
11
10
1
X (don't care)
external resistor
Ambient Light Sensing and Target Light
Calculation
A/D
Zone
Averager
Zline 0
8 bits
Zline 1
Zline 2
Input light
zone
definition
registers
Zline 3
User selectable with
typical defaults
Z0 target light
Z1 target light
Z2 target light
Z3 target light
Z4 target light
Discriminator
8 bits
8 bits
8 bits
8 bits
8 bits
0
1
7 bits
2
3
ALS Target
Value
To Ambient
Light
Calculation
4
User selectable with
typical defaults
Figure 20. Ambient Light Sensing and Target Light Calculation
28
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Ambient Light Calculation
Value selected for
Ramp Control
Ramp from previous
value to Target value
ALS_EN_G1 bit
selection
Group 1
fader value
0
0
Ambient Light
Calculation results
to Dynamic
Backlight Control
(if enabled) or
directly to LED
Mapping (when
DBC disabled)
Ramp
control
X
-
1
1
Group 1
fade times
ALS_EN_G2 bit
selection
Group 2
fader value
0
0
Ramp
control
X
1
Group 2
fade times
-
ALS Target
Value from
Ambient Light
Sensing and
Target Light
Calculation
1
ALS_EN_G3 bit
selection
Group 3
fader value
0
0
Ramp
control
X
-
1
1
Group 3
fade times
Figure 21. Ambient Light Calculation
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Dynamic Backlight Control
0
-
X
1
PWM_SEL_G2
Inputs from
Ambient Light
Calculation
0
LED
Mapping
-
X
1
PWM_SEL_G3
0
-
X
1
PWM Input ± pin
Dynamic Backlight Control
Figure 22. Ambient Light Sensing Functionality
The ALS circuit has four programmable thresholds which define five ambient brightness zones. The Zline0 –
Zline3 and Z0 Target Light – Z4 Target Light registers control the user-selectable thresholds and brightness
levels for the different zones. It is also possible to set the start value from which the ALS starts when enabled.
ALS start zone can be selected with 3 bits in ALS_START_VALUE control register 1BH, as shown in Table 38to
following table . ALS start zone will be taken after startup or after power-save. ALS zone data is readable from
register 97H.
When ALS has changed from zone to another, the ALS_ZONE_CHANGE bit in the STATUS/INTERRUPT
register (3AH) is set to '1'. Reading this register clears the bit. When an interrupt is wanted from ALS zone, the
MASK_ALS_ZONE_INT bit in MISC register (36H), must be set to '0'. This bit is '1' by default. When this bit it set
to '0' ALS gives interrupt when zone changes, and INT output will go to into a low state. Read-back of the
Status/Interrupt register will cause the INT output to go to a high state.
Table 38. ALS Start Zone Selection
30
zone_start[2:0]
ALS start value
000
Zone 0 target value
001
Zone 1 target value
010
Zone 2 target value
011
Zone 3 target value
100
Zone 4 target value
101
ALS remembers last value after power-save
110
ALS remembers last value after powe—r-save
111
ALS remembers last value after power-save
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The ambient light sensor input has a 0 to 1V operational input voltage range. The voltage at ALS1 or ALS2 is
compared with the 8-bit values programmed into the Zline0-Zline3 registers. When the ambient light sensor
output crosses one of the Zline0 – Zline3 programmed thresholds, the internal ALS circuitry will smoothly
transition the LED current to the new 8-bit brightness level as programmed into the Z0 target light – Z4 target
light registers. The averaging time for ALS to be configured with 3 bits in ALS control register 11H is described in
following table . The averaging time is designed to remove fast changes in lighting conditions.
Table 39. ALS Averaging Time Selection
AVGT[2:0]
Average time (ms)
000
4
001
8
010
16
011
32
100
64
101
128
110
256
111
512
Vals_ref=1V
Zone 4
Zone 3
Zline 2
Zline 1
LED Current
Vsense
Zline 3
Zone 2
Zline 0
Zone 1
Zone 0
Z0T
Ambient Light (lux)
Z1T
Z2T
Z3T
Z4T
Percentage of full scale
Table 40. Zline 0 (Threshold 0 Select)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Data
Data
Data
Data
Data
Data
Data
Data
Table 41. Zline 1 (Threshold 1 Select)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Data
Data
Data
Data
Data
Data
Data
Data
Table 42. Zline 2 (Threshold 2 Select)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Data
Data
Data
Data
Data
Data
Data
Data
Table 43. Zline 3 (Threshold 3 Select)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Data
Data
Data
Data
Data
Data
Data
Data
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Table 44. Z0 Target Light (Brightness Translation 1)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
1
Data
Data
Data
Data
Data
Data
Data
Table 45. Z1 Target Light (Brightness Translation 2)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
1
Data
Data
Data
Data
Data
Data
Data
Table 46. Z2 Target Light (Brightness Translation 3)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
1
Data
Data
Data
Data
Data
Data
Data
Table 47. Z3 Target Light (Brightness Translation 4)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
1
Data
Data
Data
Data
Data
Data
Data
Table 48. Z4 Target Light (Brightness Translation 5)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
1
Data
Data
Data
Data
Data
Data
Data
GENERAL PURPOSE ADC
LM8502 has a built-in analog-to-digital converter (ADC) that can be used, for example, for LED error detection or
sensor input for the lighting engines. The general purpose ADC provides an opportunity to measure the forward
voltages of the LED outputs as well as flash outputs and Indicator LED Output. Voltage on ALS1 input, boost
converter output voltage VOUT and voltage in INT pin can also be measured with the ADC. The ADC is activated
by serial interface write and the result can be read through the serial interface during the next cycle. Table 49
describes how to select correct output to be measured.
One can also connect some sensors or audio input for getting sensor or audio synchronization information into
lighting engines via ADC. Values from ADC to lighting engines are passed with variables. The ADC can convert
positive signals from 0 to 5V.
Table 49. General Purpose ADC Conversion Table
32
adc_test_ctrl[4:0]
ADC Output
00000
LED Output 1
00001
LED Output 2
00010
LED Output 3
00011
LED Output 4
00100
LED Output 5
00101
LED Output 6
00110
LED Output 7
00111
LED Output 8
01000
LED Output 9
01001
LED Output 10
01010
FLASH Output 1
01011
FLASH Output 2
01100
Indicator LED Output
01101
Not used
01110
Not used
01111
VOUT
10000
ALS1 input
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Table 49. General Purpose ADC Conversion Table (continued)
10001
INT pin
10010 – 11111
Not used
THERMAL SHUTDOWN
When the LM8502's die temperature reaches +150°C, the boost converter shuts down and the NFET and PFET
turn off. Additionally, both flash sources (FLASH1 and FLASH2) turn off. When the thermal shutdown threshold is
tripped a '1' is written to bit [1] of the Flag register (Thermal Shutdown bit). The LM8502 will start up again when
the die temperature falls to below +135°C.
During heavy load conditions when the internal power dissipation in the device causes thermal shutdown, the
part will turn off and start up again after the die temperature cools down. This will result in a pulsed on/off
operation.
PWM/ENVM/TX2 PIN
The PWM/ENVM/TX2 pin can be configured as a PWM input, as an external voltage mode enable, or as a power
amplifier synchronization. PWM input can be enabled from register 3BH bit [0]. Setting this bit to '0' enables
PWM and disables ENVM/TX2.
Table 50. PWM Configuration
INT_pin configuration
PWM_CONFIG (bit [0] register 3BH
PWM input enabled, ENVM/TX2 disabled
0
PWM input disabled, ENVM/TX2 enabled
1
When the PWM input is enabled the LED current becomes a function of the code in the group brightness register
and the duty cycle at PWM. The PWM input accepts a logic level input with selectable minimum frequencies of
100 Hz, 500 Hz, 1 kHz, and 5 kHz. Internal filtering of the PWM input frequency converts the duty cycle
information to an average control signal which directly controls the LED current. Table 51 displays latency
information for different PWM minimum frequency selections. Minimum frequency can be selected from DBC
control register 1DH.
Table 51. PWM Frequency Control
pwm_min_freq control (Hz)
Latency, PWM (100% to 0%), ms
Latency, PWM (0% to 100%), ms
100
13.6
12.2
500
3
2.9
1000
1.7
1.7
5000
0.45
0.7
The PWM input is designed so that it works through the group controls. LED outputs, which should be controlled
by the PWM, need to be grouped into one of the three groups. There is an enable for each group that selects
whether the PWM affects a certain group or not. One group of LED outputs could be affected by PWM whereas
another might only be controlled from a group fader register. After the PWM input is multiplied with the group
brightness setting, and possibly also with the ALS0, it is mapped into LED outputs.
ENVM and TX2 are explained in more detail in the Flash section.
INT PIN
The INT pin is used for informing the microcontroller when a lighting sequence is finished, when ALS changes
zone, or when the general purpose ADC has finished its measurement. The INT signal is active low, i.e., when
an interrupt signal is sent, and the pin is pulled to GND. The INT pin can be configured with bit [1] in register
3BH. Setting this bit to '0' enables the INT; setting it to '1' connects the INT to the general purpose ADC. An
external pull-up resistor is needed for proper functionality.
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TRIG PIN
The TRIG pin can function as an external trigger input or output. External trigger signal is active low when a
trigger is sent or received, and the pin is pulled to GND. TRIG is an open-drain pin, and an external pull-up
resistor is needed for trigger line. An external trigger input signal must be at least two 32 kHz clock cycles long to
be recognized. The trigger output signal is three 32 kHz clock cycles long. If TRIG pin is not used on application,
it should be connected to GND to prevent floating of this pin and extra current consumption.
CLK PIN
The CLK pin is used for connecting an external 32 kHz clock to the LM8502. Using an external clock can
improve automatic Power-save mode efficiency because the internal clock can be switched off automatically
when device has entered Power-save mode and an external clock is present. The device can be used without an
external clock. If an external clock is not used on the application, the CLK pin should be connected to GND to
prevent floating of this pin and extra current consumption.
POWER SAVING
The LM8502 includes Power-save mode which allows lower current consumption when the device is not active.
Additional power can be saved using an external 32 kHz clock input. Automatic Power-save mode is enabled
when the POWERSAVE_EN bit in register is ‘1’. Almost all analog blocks are powered down in Power-save if an
external clock signal is used. Only the protection circuits remain active. However, if the internal clock has been
selected, only the boost converter and LED drivers are disabled during the power-save; the digital part of the
LED controller needs to stay active. During the program execution the LM8502 can enter Power-save if there is
no activity in any of the LED driver outputs. To prevent short power-save sequences during program execution,
the device has an instruction look-ahead filter. During program execution engine 1 and engine 2 instructions are
constantly analyzed, and if there are time slots with no activity on LED driver outputs for 50 ms, the device will
enter Power-save. In Power-save mode program execution continues uninterruptedly. When an instruction that
requires activity is executed, a fast internal startup sequence will be started automatically.
Powersave mode if
brightness = 0
longer than 50 ms
LED brightness
POWER
SAVE
POWERSAVE
Time
Chip current consumption
(LED current not included)
Time
Figure 23. The Effect of Power-Save Mode During a Lighting Sequence
BOOST CONVERTER
The LM8502 has a 2 MHz fixed-frequency synchronous boost converter. The boost converter has two modes:
Constant Voltage Output mode and Adaptive Voltage mode. On startup, when VOUT is less than VIN, the internal
synchronous PFET turns on as a current source and delivers 350 mA (typ.) to the output capacitor. During this
time all LED outputs are off. When the voltage across the output capacitor reaches 2.2V, the LED outputs can
turn on.
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Constant Voltage Output Mode
In Constant Voltage Output mode the LM8502 operates as a voltage output boost converter with selectable
output voltages of 4.5V and 5V. In Constant Voltage Output mode the LM8502 is able to deliver up to 5W of
output power.
Constant Voltage Output mode is enabled by Bit 2 (VM) of the Torch Brightness register or Flash Brightness
register, with the ENVM input or with the EN_HAPTIC bit. Write a '1' to bit [1] of Configuration Register 1 to set
VOUT to 5V. Write a '0' to this bit to set VOUT to 4.5V. In Constant Voltage Output mode the flash LED current
sources continue to operate; however, the difference between VOUT and VLED will be dropped across the current
sources. In Constant Voltage Output mode when VIN is greater than VOUT, the LM8502 operates in Pass mode.
Adaptive Voltage Mode
In Adaptive Voltage mode the adaptive boost control is enabled, and the output voltage is kept at optimum level.
When the flash outputs are on, and if the output voltage is greater than VIN – 150 mV, the PWM converter
switches and maintains at least 300 mV across flash LED outputs.
When flash LEDs are not on, the converter maintains at least 70 mV across the low-side LED outputs. Converter
voltage is raised in steps from 3.125V up to 5V in 125 mV steps to ensure that the LED outputs remain in
regulation. When the input voltage rises above the LED voltage + headroom voltage, the device operates in Pass
mode.
When flash and low-side LED outputs are both on, starting level and maximum level for the voltage-over-flash
LED driver can be defined. These levels are defined in register 35H according to following table:
Table 52. Adaptive Flash Control Register 35H
FLASH_START[7:4]
FLASH_MAX[3:0]
Voltage-over-flash LED driver (mV)
0000
0000
300
0001
0001
400
0010
0010
500
0011
0011
600
0100
0100
700
0101
0101
800
0110
0110
900
0111
0111
1000
1000
1000
1100
1001
1001
1200
1010
1010
1300
1011
1011
1400
1100
1100
1500
1101
1101
1600
1110
1110
1700
1111
1111
1800
PASS MODE
If the difference between VOUT and VLED is greater than 300 mV the device operates in Pass mode. In Pass
mode the boost converter stops switching and the synchronous PFET turns fully on bringing VOUT up to VIN – IIN
× RPMOS (RPMOS = 150mΩ). In Pass mode the inductor current is not limited by the peak current limit. In this
situation the output current must be limited to 2.5A.
If the device is operating in Pass mode, and VIN drops to a point that forces the device into switching, the
LM8502 will make a one-time decision to jump into Switching mode. The LM8502 remains in Switching mode
until the device is shut down and re-enabled. This is true even if VIN were to rise back above VFLASH LED + 300
mV . This prevents the LED current from oscillating when VIN is operating close to VOUT.
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LIGHT LOAD
At light loads, whether in Constant Voltage mode or Adaptive Voltage mode, the PWM switching converter
changes over to a pulsed frequency regulation scheme (light-load comparator enabled) and only switches as
necessary to ensure proper LED current or output voltage regulation. This allows for improved light load
efficiency compared to converters that operate in fixed frequency PWM mode at all load currents. In this mode
the device will only switch as necessary to maintain VOUT within regulation. This mode provides a better
efficiency due to the reduction in switching losses which become a larger portion of the total power loss at light
loads.
Configuration Register 1 bit [0] = 1 disables the light-load comparator. With this bit set to '0' (default) the light
load comparator is enabled. When flash LEDs are enabled the light load comparator is always disabled. When
the light load comparator is disabled the LM8502 will operate at a constant frequency down to ILOAD = 0.
Disabling light load can be useful when a more predictable switching frequency across the entire load current
range is desired.
OVER-VOLTAGE PROTECTION
The output voltage is limited to typically 5.6V (5.7V max). In situations such as when the current source is open,
the LM8502 will raise the output voltage in order to try to keep the LED current at its target value. When VOUT
reaches 5.6V the over-voltage comparator will trip and turn off both the internal NFET and PFET. When VOUT
falls below 5.4V the LM8502 will begin switching again. Note that over-voltage protection is not in use in Pass
mode.
CURRENT LIMIT
The LM8502 features 4 selectable current limits 1A, 1.5A, 2A, and 2.5A. These are controlled through the I2Ccompatible interface via bits [6:5] of the Flash Duration register. When the current limit is reached the LM8502
stops switching for the remainder of the switching cycle.
Since the current limit is sensed in the NMOS switch there is no mechanism to limit the current when the device
operates in Pass mode. In situations where there could potentially be large load currents at OUT, and the
LM8502 is operating in Pass mode, the load current must be limited to 2.5A. In Boost mode or Pass mode, if
VOUT falls below approximately 2.3V, the part stops switching, and the PFET operates as a current source
limiting the current to typically 350 mA. This prevents damage to the LM8502 and excessive current draw from
the battery during output short circuit conditions.
MAXIMUM OUTPUT POWER
Output power is limited by three things: the peak current limit, the ambient temperature, and the maximum power
dissipation in the package. If the LM8502 ’s die temperature is below the absolute maximum rating of +125°C,
the maximum output power can be over 6W. However, any additional output current will cause the internal power
dissipation to increase and, therefore increase the die temperature. This can be additionally compounded if the
flash LED current sources are operating since the difference between VOUT and VLED is dropped across the
current sources. Any circuit configuration must ensure that the die temperature remains below +125°C taking into
account the ambient temperature derating.
PDISS =
(VOUT ± VIN) x VOUT
VIN
2
x RNFET +
VOUT
VIN
x RPFET x ILOAD2 + PDISSLED
PDISSLED = (VOUT ± VFLASH) x IFLASH + (VOUT ± VIND) x IIND + (VOUT ± VLEDS) x ILEDS
ILOAD = IOUT + IFLASH + IIND + ILEDS
IFLASH = IFLASH1 + IFLASH2
(1)
The above formulas consider the average current through the NFET and PFET. The actual power losses may be
higher due to the RMS currents and the quiescent power. This equation, however, gives a decent approximation.
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FLASH
Flash Brightness
Register
Flash
mode
Brightness
Fader
(16 Ps/step)
Brightness control to flash driver
Torch
mode
Flash control
signal
Torch Brightness
Register
External pins
Flash control via external pins STROBE,
TX1, TX2, NTC or via i2c regs
or via VIN Monitor
Strobe
TX1
TX2
NTC
Timeout Counter
Flash Control
VIN Monitor
Flash_stop
I2C
Registers
Flash_stop
Flash time out
register
Flash Startup
Turn on of the flash in the LM8502 is done through bits [2:0] of the Torch Brightness register (A0H), bits [2:0] of
the Flash Brightness register (B0H), or by pulling the STROBE pin high. Bits [1:0] of the Torch Brightness
register or Flash Brightness register set the current sources into Flash = '11', Torch = '10' or Indicator = '01'
mode (outputs FLASH1, FLASH2, and LEDI). At turn-on the current sources step through each level until the
target LED current is reached (16 µs/step). This gives the device a controlled turn-on and limits inrush current
from the VIN supply.
Table 53. Flash Modes
EN1 and EN0 bits in Registers A0H or B0H
Flash Mode
00
Flash Shutdown
01
Indicator Mode
10
Torch Mode
11
Flash mode
Table 54. Flash Registers
Register
Bit [7]
Bit [6]
TORCH BRIGHTNESS
A0H
INDICATOR LED
CURRENT
FLASH BRIGHTNESS
B0H
STR
FLASH DURATION C0H
Bit [5]
UVLO FLAG
CONFIG REGISTER 1
E0H
TX1/TORCH
CONFIG REGISTER 2
F0H
UVLO_LEVEL
Bit [3]
FLASH CURRENT
CURRENT LIMIT
FLAG REGISTER D0H
Bit [4]
TORCH CURRENT
NTC FLAG
TX2
POLARIT
Y
Bit [2]
Bit [1]
Bit [0]
VM
EN1
EN0
VM
EN1
EN0
FLASH TIMEOUT
TX2 FLAG TX1 FLAG
FLASH LED TSD FLAG
FAULT
FLAHS
TIMEOUT
FLAG
TX2_PIN_CO NTC_HYS LEDI_NTC
NFIG
T
DIS_EXT_S VM_VALUE DIS_PFM
TROBE
EN_UVLO
AET_MODE NTC_MOD
E
EN_NTC_I UVLO_MOD
NTERRUP E
T
TX2
SHUTDOW
N
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Flash Mode
In Flash mode the LED current sources (FLASH1 and FLASH2) each provide 16 different current levels from
37.5 mA to 600 mA in steps of 37.5 mA (see Table 55). The Flash currents are adjusted by writing to bits [6:3] of
the Flash Brightness register, and Flash mode is enabled by writing '11' to Torch Brightness register or Flash
Brightness register bits [1:0].
Table 55. Flash Currents
Flash Current Bits [6:3] in Register B0H
Flash Current (mA)/Output
0000
37.5
0001
75
0010
112.5
0011
150
0100
187.5
0101
225
0110
262.5
0111
300
1000
337.5
1001
375
1010
412.5
1011
450
1100
487.5
1101
525
1110
562.5
1111
600
Flash Timeout
The Flash Timeout period sets the amount of time that the Flash Current is being sourced from current sources
FLASH1 and FLASH2. Bits [4:0] of the Flash Duration register set the Flash Timeout period. There are 32
different Flash Timeout levels in steps of 32 ms giving a Flash Timeout range of 32 ms to 1024 ms. When
timeout expires before Flash pulse is terminated, the FLASH_TIME_OUT bit in Flag Register D0H is set to '1'.
This flag is reset to '0' by pulling EN pin low, removing power from the LM8502, or when the next Flash pulse is
triggered.
Torch Mode
In Torch mode the current sources FLASH1 and FLASH2 each provide 8 different current levels. (See Table 56).
The Torch currents are adjusted by writing to bits [5:3] of the Torch Brightness register. Torch mode is activated
by setting Torch Brightness register or Flash Brightness bits [1:0] to '10'. Once the Torch mode is enabled the
current sources will ramp up to the programmed Torch current level by stepping through all of the Torch currents
at (16 µs/step) until the programmed Torch current level is reached.
Table 56. Torch Currents
38
Torch Current Bits [5:3] in Register A0H
Torch Current (mA)/Output
000
18.75
001
37.5
010
56.25
011
75
100
93.75
101
112.5
110
131.25
111
150
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STROBE
Bit [7] of the Flash Brightness register (STR bit) determines how the Flash pulse terminates. With the STR bit = 1
the Flash current pulse will only terminate by reaching the end of the Flash Timeout period. With STR = 0, Flash
mode can be terminated by pulling STROBE low, programming bits [1:0] of the Torch Brightness register, or the
Flash Brightness register to '00', or by allowing the Flash Timeout period to elapse. If STR = 0, and STROBE is
toggled before the end of the Flash Timeout period, the Timeout period resets on the rising edge of STROBE.
See LM8502 Timing Diagrams regarding the Flash pulse termination for the different STR bit settings.
After the Flash pulse terminates, either by a flash timeout, pulling STROBE low, or disabling it via the I2Ccompatible interface, FLASH1 and FLASH2 turn completely off. This happens even when Torch is enabled via
the I2C-compatible interface, and the Flash pulse is turned on by toggling STROBE. After a Flash event ends the
EN1 and EN0 bits (bits [1:0] of the Torch Brightness register or Flash Brightness register) are automatically rewritten with '00'.
Power Amplifier Synchronization (TX1)
The TX1/TORCH input has a dual function. When Configuration register 1 bit [7] = 0 (default), EOH TX1/TORCH
is a power amplifier synchronization input. This is designed to reduce the current pulled from the battery during
an RF power amplifier transmit event. When the LM8502 is engaged in a Flash event, and the TX1/TORCH pin
is pulled high, both FLASH1 and FLASH2 are forced into Torch mode at the programmed Torch current setting. If
the TX1/TORCH pin is then pulled low before the Flash pulse terminates, the LED current will ramp back to the
previous Flash current level. At the end of the Flash timeout, whether the TX1/TORCH pin is high or low, the
LED current will turn off.
When Configuration Register 1 bit [7] = 1, TX1/TORCH is configured as a hardware Torch mode enable. In this
mode a high at TX1/TORCH turns on the LED current sources in Torch mode. TX1/TORCH will take precedence
over the STROBE input and Flash/Torch bit settings of the Torch Brightness register bits [1:0] and the Flash
Brightness register bits [1:0].
The TX1 interrupt flag (bit [3]) indicates a TX event on the TX1/TORCH pin. Bit [3] will read back a '1' if
TX1/TORCH is in TX1 mode, and the pin has changed from low to high since the last read of the Flag register. A
read of the Flag Register automatically resets this bit.
PWM/ENVM/TX2
The PWM/ENVM/TX2 input has three functions. (See above for explanation of PWM function.) ENVM/TX2 can
be enabled from bit [0] of register 3BH. Setting this PWM_CONFIG bit to '1' disables PWM and enables
ENVM/TX2.
In ENVM mode (Configuration register 1 bit [5] = 0) the ENVM/TX2 pin is an active high-logic input that forces
the LM8502 into Voltage Output mode. In TX2 mode (Configuration Register 1 bit [5] = 1) the ENVM/TX2 pin is a
power amplifier synchronization input that forces the LM8502 from Flash mode into Torch mode.
In TX2 mode, when Configuration Register 1 bit [6] = 0 the ENVM/TX2 input is an active low-transmitinterrupt
input. When Configuration Register 1 bit [6] = 1 the ENVM/TX2 input is an active high-transmit interrupt. Under
this condition when the LM8502 is engaged in a Flash event, and ENVM/TX2 is pulled low (bit = 0) or high (bit =
1), both FLASH1 and FLASH2 are forced into either Torch mode or LED shutdown, depending on the logic state
of Configuration Rregister 2 bit [0]. After a TX2 event, if the ENVM/TX2 input is disengaged, and the TX2
Shutdown bit is set to force Torch mode, the LED current will ramp back to the previous Flash current level. If the
TX2 shutdown bit is programmed to force LED shutdown at a TX2 event, the Flag register must be read to
resume normal LED operation.
The TX2 interrupt flag (bit [4]) indicates a TX event on the ENVM/TX2 pin. Bit [4] will read back a '1' if ENVM/TX2
is in TX2 mode, and the pin has had a TX event since the last read of the Flag register. A read of the Flag
Register automatically resets this bit.
Indicator LED/Thermistor (LEDI/NTC)
The LEDI/NTC pin serves a dual function, either as an LED indicator driver or as a threshold detector for a
negative temperature coefficient (NTC) thermistor.
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LED Indicator Mode (LEDI)
LEDI/NTC is configured as an LED indicator driver by setting Configuration register 1 bit [3] = '0' and Torch
Brightness register or Flash Brightness register bits [1:0] = '01'. In Indicator mode there are 4 different current
levels available (2.3 mA, 4.6 mA, 7.9 mA, 9.2 mA). Bits [7:6] of the Torch Brightness register set the 4 different
indicator current levels.
Thermal Comparator Mode (NTC)
Writing a '1' to Configuration register 1 bit [3] disables the indicator current source and configures the LEDI/NTC
pin as a detector for a NTC thermistor. In this mode the LEDI/NTC becomes the negative input of an internal
comparator with the positive input internally connected to a reference (VTRIP = 1V). Additionally, Configuration
register 2 bit [1] determines what action the device takes if the voltage at LEDI/NTC falls below VTRIP (while the
device is in NTC mode). With Configuration register 2 bit [1] = 0, the LM8502 will be forced into Torch mode
when the voltage at LEDI/NTC falls below VTRIP. With Configuration register 2 bit [1] = 1 the device will shut
down the current sources when VLEDI/NTC falls below VTRIP. Two software-selectable hysteresis levels are
available for NTC mode. Configuration register 1 Bit [4] = 0 selects 125 mV of hysteresis. When this bit is set to 1
there is 250 mV of hysteresis in NTC mode.
The NTC flag bit [5] of the Flag Register reads back a '1' if the LM8502 is active in Flash or Torch mode, the
device is in NTC mode, and the voltage at LEDI/NTC has fallen below VTRIP. When this has happened, and the
LM8502 has been forced into Torch or LED shutdown (depending on the state of Configuration Register 2 bit
[1]), the Flag Register must be read, and the voltage at the LEDI/NTC pin goes above VTRIP + hysteresis in order
to place the device back in normal operation. For example, if the NTC mode has been selected (Configuration
Register 1 bit [3] = 1) and programmed to force Torch mode while the device is flashing during an NTC event,
the LEDs will then be forced into Torch mode. Until the Flag Register is read back, the LEDs will only be able to
flash at the programmed Torch current level. On the other hand, if LED shutdown is selected, the LEDs will
remain off regardless of the state of the LED enable bits and STROBE until the Flag Register is read back.
Alternative External Torch Mode
Configuration Register 2 bit [2] programs the LM8502 for Alternative External Torch mode. With this bit set to '0'
(default), TX1/TORCH is a transmit interrupt that forces Torch mode only during a Flash event. For example, if
TX1/TORCH goes high during a Flash event, the LEDs will be forced into Torch mode only for the duration of the
timeout counter. At the end of the timeout counter the LEDs will turn off.
With Configuration Register 2 bit [2] set to '1' the operation of TX1/TORCH depends on STROBE. In this mode if
TX1/TORCH goes first, and then STROBE goes high, the LEDs are forced into Torch mode with no timeout. If
TX1/TORCH goes high after STROBE has gone high, then the TX1/TORCH pin operates as a normal TX
interrupt, and the Flash LEDs will turn off at the end of the timeout duration.
Input Voltage Monitor
The LM8502 has an internal comparator that monitors the voltage at VIN and can force the flash LED current into
Torch mode or into shutdown if VIN falls below the programmable Undervoltage Lockout Threshold. Bit 5 in
Configuration Register 2 F0H enables or disables the feature. When enabled, Bits [1] and [2] program the 4
adjustable thresholds of 3.1V, 3.2V, 3.3V and 3.4V. Bit [3] in Configuration Register 2 F0H selects whether an
undervoltage event forces Torch mode or forces the flash LEDs off.
There is a set 100 mV hysteresis for the input voltage monitor. When the input voltage monitor is active, and VIN
falls below the programmed UVLO threshold, the flash LEDs will either turn off or their current will be reduced to
the programmed Torch current setting. To reset the flash LED current to its previous level, two things must occur.
First, VIN must go at least 100 mV above the UVLO threshold; secondly, the Flag register must be read back.
The UVLO flag (bit [6] of the Flag Register) reads back a '1' when the Input Voltage Monitor is enabled and VIN
falls below the programmed UVLO threshold. This flag must be read back in order to resume normal operation
after the LED current has been forced to Torch mode or turned off due to a UVLO event.
Flash LED Fault
The LED Fault flag (bit [2] of the Flag Register) reads back a '1' if the part is active in Flash or Torch mode, and
either FLASH1 or FLASH2 experience an open or short condition. An LED open condition is signaled if the OVP
threshold is crossed at OUT while the device is in either Flash or Torch modes. An LED short condition is
signaled if the voltage at FLASH1 or FLASH2 goes below 500 mV while the device is in Torch or Flash modes.
40
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There is a small delay before the flash fault flag is valid. This delay is the time between when the Flash or Torch
current is triggered and the LED voltage and the output voltage is sampled. The flash fault flag can only be reset
to '0' by pulling EN pin low or removing power to the LM8502.
LM8502 Timing Diagrams
I2C Torch
Command
Default State
Flash Brightness Register bit 7 (STR) = 0
Configuration Register bit 7 (TX1/TORCH) = 0
Configuration Register bit 6 (TX2 Polarity) = 1
Configuration Register bit 5 (ENVM/TX2) = 0
Flash Duration bit 7 (SEM) = 0
STROBE
I
FLASH
I TORCH
I LED
Timeout
Duration
Normal Torch to Flash Operation
(Default, Power On or RESET state of LM8502)
TX1/TORCH
STROBE
Default State
(TX event during a STROBE event)
I FLASH
I TORCH
I LED
Timeout
Duration
TX1 Event During a Flash Event
(Default State,TX1/TORCH is an Active High TX Input)
TX1/TORCH
STROBE
I LED
Default State
(TX1 event before and after STROBE event)
I TORCH
Timeout
Duration
TX1 Event Before and After Flash Event
(Default State, TX1/TORCH is an Active High TX Input
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I2C Torch
Command
Default State
STROBE goes high and the LEDs turn on into Flash
mode. LEDs will turn off at the end of timeout
duration or when STROBE goes low. Everytime
STROBE goes high the timeout resets.
STROBE
I FLASH
I TORCH
ILED
Timeout
Duration
Start of
Timeout
Counter
Timeout
Counter
Reset
STROBE Input is Level Sensitive
(Default State, STR bit = 0)
I2C Torch
Command
STROBE
Flash Brightness Register bit 7 (STR) = 1
STROBE goes high and the LEDs turn on into Flash
mode. LEDs will stay on for the timeout duration even
if STROBE goes low before.
IFLASH
I TORCH
I LED
Timeout
Duration
STROBE Input is Edge Sensitive
(STR bit = 1)
I2C Torch
Command
ENVM/TX2
ENVM/TX2 as a transmit interrupt
Configuration Register bit 5 (ENVM/TX2) = 1
(ENVM/TX2 operates as a transmit interrupt )
STROBE
I FLASH
I TORCH
ILED
Timeout
Duration
ENVM/TX2 Pin is Configured as an Active High TX Input
I2C-Compatible Interface
The I2C-compatible synchronous serial interface provides access to the programmable functions and registers on
the device. This protocol uses a two-wire interface for bidirectional communications between the IC's connected
to the bus. The two interface lines are the Serial Data Line (SDA), and the Serial Clock Line (SCL). Every device
on the bus is assigned a unique address and acts as either a Master or a Slave depending on whether it
generates or receives the serial clock SCL. The SCL and SDA lines should each have a pull-up resistor placed
somewhere on the line and remain HIGH even when the bus is idle. Note: CLK pin is not used for serial bus data
transfer. The LM8502 supports high speed I2C.
DATA VALIDITY
The data on SDA line must be stable during the HIGH period of the clock signal (SCL). In other words, state of
the data line can only be changed when clock signal is LOW.
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SCL
SDA
data
change
allowed
data
valid
data
change
allowed
data
valid
data
change
allowed
Figure 24. Data Validity Diagram
START AND STOP CONDITIONS
The LM8502 is controlled via an I2C-compatible interface. START and STOP conditions classify the beginning
and end of the I2C session. A START condition is defined as SDA transitions from HIGH to LOW while SCL is
HIGH. A STOP condition is defined as SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master
always generates the START and STOP conditions.
SDA
SCL
S
P
Start Condition
Stop Condition
Figure 25. Start and Stop Sequences
The I2C bus is considered busy after a START condition and free after a STOP condition. During data
transmission the I2C master can generate repeated START conditions. A START and a repeated START
condition are equivalent function-wise. The data on SDA must be stable during the HIGH period of the clock
signal (SCL). In other words, the state of SDA can only be changed when SCL is LOW. shows the SDA and SCL
signal timing for the I2C-Compatible Bus. See the Electrical Tables for timing values.
t1
SCL
t5
t4
SDA_IN
t2
SDA_OUT
t3
Figure 26. I2C-Compatible Timing
TRANSFERRING DATA
Every byte put on the SDA line must be eight bits long, with the most significant bit (MSB) being transferred first.
Each byte of data has to be followed by an acknowledge bit. The acknowledge related clock pulse is generated
by the master. The master releases the SDA line (HIGH) during the acknowledge clock pulse. The LM8502 pulls
down the SDA line during the 9th clock pulse, signifying an acknowledge. The M8502 generates an acknowledge
after each byte has been received.
There is one exception to the “acknowledge after every byte” rule. When the master is the receiver, it must
indicate to the transmitter an end of data by not-acknowledging (“negative acknowledge”) the last byte clocked
out of the slave. This “negative acknowledge” still includes the acknowledge clock pulse (generated by the
master), but the SDA line is not pulled down.
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After the START condition, the bus master sends a chip address. This address is seven bits long followed by an
eighth bit which is a data direction bit (READ or WRITE). For the eighth bit, a “0” indicates a WRITE and a “1”
indicates a READ. The second byte selects the register to which the data will be written. The third byte contains
data to write to the selected register.
ack from slave
ack from slave
ack from slave
start
MSB Chip Addr LSB
w
ack
MSB Register Addr LSB
ack
MSB
Data LSB
ack
stop
start
id = 33h
w
ack
addr = 40h
ack
address 40h data
ack
stop
SCL
SDA
(w = write; SDA = '0'), id = device address = 33H for LM8502
Figure 27. Write Cycle
ack from slave
start
MSB Chip Addr LSB
w
ack from slave
MSB Register Addr LSB
repeated start
ack from slave data from slave nack from master
rs
MSB Chip Address LSB
rs
id = 33h
r
MSB
Data
LSB
stop
address 3Fh data
nack stop
SCL
SDA
start
id =33h
w ack
address = 3Fh
ack
r ack
( r = read; SDA = '1'), id = device address = 33H for LM8502. When READ function is to be accomplished, a WRITE
function must precede the READ function as shown above.
Figure 28. Read Cycle
I2C-COMPATIBLE CHIP ADDRESS
The device address for the LM8502 is '0011 0011' (33H). After the START condition, the I2C master sends the 7bit address followed by an eighth bit, read or write (R/W). R/W = 0 indicates a WRITE, and R/W = 1 indicates a
READ. The second byte following the device address selects the register address to which the data will be
written. The third byte contains the data for the selected register.
MSB
1
Bit 7
LSB
0
Bit 6
1
Bit 5
0
Bit 4
0
Bit 3
1
Bit 2
1
Bit 1
R/W
Bit 0
2
I C Slave Address (chip address)
Figure 29. Device Address
AUTO INCREMENT FEATURE
The auto increment feature allows writing several consecutive registers within one transmission. Every time an 8bit word is sent to the LM8502, the internal address index counter will be incremented by one, and the next
register will be written. The table below shows writing a sequence to two consecutive registers. Note that auto
increment feature does not work for read.
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Table 57. Auto Increment Example
Master
Start
Device
Address
= 33H
Register
Address
Write
LM8502
ACK
Data
ACK
Data
ACK
Stop
ACK
Register Descriptions
The LM8502 is controlled with set of registers through the I2C-compatible interface. Table 58 below lists device
registers, their addresses and abbreviations.
Table 58. Detailed Register Descriptions
Hex
Address
Register Name
Bit(s) in
Use
[6]
00
ENABLE/ENGINE
CNTRL1
[5:4]
[3:2]
01
Read/Write
R/W
R/W
R/W
Bit Default
Value After
Reset
Bit Mnemonic and Description
0
CHIP_EN
0 = LM8502 not enabled. Device enters Standby mode.
Control registers can be written or read.
1 = LM8502 enabled and internal startup sequence
powers up all needed internal blocks and device enters
Normal mode.
00
ENGINE1_EXEC
Engine 1 program execution control. Execution register
bits define how the program is executed. Program start
address can be programmed to Program Counter (PC)
register 37H.
00 = Hold: Hold causes the execution engine to finish
current instruction and the stop. PC can be read or
written only in this mode.
01 = Step: Execute the instruction at the location pointed
by PC, increment PC by one and then reset
ENG1_EXEC bits to 00.
10 = Free Run: Start program execution from the
instruction pointed by PC.
11 = Execute Once: Execute the instruction pointed by
the current PC value and reset ENG1_EXEC to 00. The
difference between step and execute once is that execute
once does not increment PC.
00
ENGINE2_EXEC
Engine 2 program execution control. Equivalent to engine
1 control bit. Program start address can be programmed
to PC register 38H.
[5:4]
R/W
00
ENGINE1_MODE
Engine 1 mode control:
00 = Disabled: Engines can be configured to disabled
mode separately.
01 = Load program to SRAM memory, reset PC. Writing
to program memory is allowed only when the engine is in
load program mode and engine busy bit (3AH) is not set.
Serial bus master should check the busy bit before
writing to program memory. Both engines are in hold
while one is in Load mode. Load mode resets the PC of
the respective engine. Load mode can be entered only
from Disabled mode. Entering Load mode from Run
mode is not allowed.
10 = Run mode executes the instructions stored in the
program memory. Engine control register bits define how
the program is executed. Program start address can be
programmed to PC register. PC is reset to zero when the
PC upper limit is reached.
11 = Halt mode halts the engine operation and instruction
execution is aborted immediately.
[3:2]
R/W
00
ENGINE2_MODE
Engine 2 mode control, same as Engine 1.
ENGINE CNTRL2
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Table 58. Detailed Register Descriptions (continued)
[7:4]
R/W
0000
FADE_IN
Fade in time for groups 1 – 3
See fade_in times in (1)
[3:0]
R/W
0000
FADE_OUT
Fade out time for groups 1 – 3
See fade_out times in (1)
GROUPS 1 – 3
FADING
02 – 04
[7:6]
06 – 0F
(1)
46
00
0
LOG_EN
Logarithmic dimming control for LED output 1 – 10. This
bit is effective for both the program execution engine
control and direct PWM control.
0 = linear adjustment
1 = logarithmic adjustment
LED 1 – 10 CONTROL
[5]
10
R/W
GROUP_SELECT
Group fader selection for LED outputs 1 – 10:
00 = LED output not grouped to any of the groups.
Default setting.
01 = Fader group 1 controls the LED output. User can set
the overall output of the group from the GROUP 1
FADER register 48H and the fade-in/out times from the
GROUP 1 FADING register 02H.
10 = Fader group 2 controls the LED output. User can set
the overall output of the group from the GROUP 2
FADER register 49H and the fade-in/out times from the
GROUP 2 FADING register 03H.
11 = Fader group 3 controls the LED output. User can set
the overall output of the group from the GROUP 3
FADER register 4AH and the fade-in/out times from the
GROUP 3 FADING register 04H.
HAPTIC_CONTROL
R/W
[4:3]
R/W
00
FULL_SCALE_SEL
Current full-scale setting for LED outputs 1 – 10:
00 = maximum LED current is 3 mA
01 = maximum LED current is 6 mA
10 = maximum LED current is 12.5 mA
11 = maximum LED current is 25.5 mA
[0]
R/W
0
LED_BAT_CON
LED outputs 1 – 10 power selection:
0 = LED powered from VOUT
1 = LED powered from external voltage supply
00
GROUP_SELECT
Group fader selection for Haptic feedback outputs:
00 = Haptic output not grouped to any of the groups.
Default setting.
01 = Fader group 1 controls the haptic output. User can
set the overall output of the group from the GROUP 1
FADER register 48H and the fade-in/out times from the
GROUP 1 FADING register 02H.
10 = Fader group 2 controls the haptic output. User can
set the overall output of the group from the GROUP 2
FADER register 49H and the fade-in/out times from the
GROUP 2 FADING register 03H.
11 = Fader group 3 controls the haptic output. User can
set the overall output of the group from the GROUP 3
FADER register 4AH and the fade-in/out times from the
GROUP 3 FADING register 04H.
[7:6]
R/W
Register I2C write has an effect when device is in Normal mode.
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Table 58. Detailed Register Descriptions (continued)
[7:5]
11
ALS_CONTROL
R/W
000
AVERAGE_TIME
ALS slope averaging time:
000 = 4 ms
001 = 8 ms
010 = 16 ms
011 = 32 ms
100 = 64 ms
101 = 128 ms
110 = 256 ms
111 = 512 ms
[4:3]
R/W
00
ALS_FUNTIONALITY
ALS functionality selection:
00 = The lowest of ALS1 or ALS2 is the ambient light
sensor input.
01 = ALS1 is the ambient light sensor inpu.t
10 = ALS2 is the ambient light sensor input.
11 = The highest of ALS1 or ALS2 is the ambient light
sensor input.
[2]
R/W
0
EN_EXT_RES
Enable external resistor use for ALS:
0 = internal resistor in use
1= external resistor in use
ALS_RES_SEL
Internal resistor selection for ALS:
00 = 1.25 kΩ
01 = 2.5 kΩ
10 = 5 kΩ
11 = 10 kΩ
[1:0]
R/W
00
12 – 15
ZLINE 0 – 3
[7:0]
R/W
00000000
INPUT LIGHT ZONE
Input light threshold zones 0 – 3 definition for ALS
16 – 1A
Z0 – Z4 TARGET
LIGHT
[7:0]
R/W
00000000
TARGET LIGHT
Target brightness levels Z0 – Z4 for ALS
1B
ALS_START_VALUE
[2:0]
R/W
000
ALS START VALUE
Starting point for ALS:
000 = Zone 0 target value
001 = Zone 1 target value
010 = Zone 2 target value
011 = Zone 3 target value
100 = Zone 4 target value
101 = ALS remembers last value after power-save
110 = ALS remembers last value after power-save
111 = ALS remembers last value after power-save
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Table 58. Detailed Register Descriptions (continued)
[7:6]
[5:3]
1D
R/W
R/W
00
PWM_MIN_FREQ
Minimum frequency setting for PWM:
00 = 100 Hz
01 = 500 Hz
10 = 1 kHz
11 = 5 kHz
000
PWM_SEL_G3–1
Selection of if the PWM input is multiplied group (or ALS
calculation if ALS_EN is set for the group) value.
000 = PWM does not affect any of the Groups
001 = PWM multiplied with G1 value
010 = PWM multiplied with G2 value
011 = PWM multiplied with G1 and G2 values
100 = PWM multplied with G3 value
101 = PWM multiplied with G1 and G3 values
110 = PWM multiplied with G2 and G3 values
111 = PWM multiplied with G1, G2 and G3 values
000
ALS_EN_G3–1
Selection of if the group value is multiplied by ALS:
001 = Group 1 value is multiplied with ALS value
010 = G2 value is multiplied with ALS value
011 = G1 and G2 values are multiplied with ALS value
100 = G3 value is multiplied with ALS value
101 = G1 and G3 values are multiplied with ALS value
110 = G2 and G3 values are multiplied with ALS value
111 = G1, G2 and G3 values are multiplied with ALS
value
00
HAPT_FREQ_SEL
Frequency selection for Haptic feedback:
00 = 157 Hz
01 = 490 Hz
10 = 980 Hz
11 = 3.9 kHz
HAPT_MODE_SEL
Mode selection for Haptic feedback:
000 = Haptic disabled
001 = PWM to both channels (2*pwm_freq)
010 = PWM on A channel, B channel in low state
011 = PWM on B channel, A channel in low state
100 = Haptic disabled
101 = PWM to both channels, no activity at center value
(2*pwm_freq)
110 = PWM on A channel, B channel in high state
111 = PWM on B channel, A channel in high state
DBC CONTROL
[2:0]
[4:3]
R/W
R/W
HAPTIC FEEDBACK
CONTROL
21
[2:0]
R/W
000
22
HAPTIC PWM DUTY
CYCLE
[7:0]
R/W
00000000
PWM_HAPT
Haptic feedback duty cycle setting
26 — 2F
LED1 – 10 CURRENT
CONTROL
[7:0]
R/W
00000000
CURRENT
LED outputs 1– 10 current control
(2)
48
(2)
.
Register I2C write has an effect when device is in Normal mode.
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Table 58. Detailed Register Descriptions (continued)
[7:4]
35
0000
FLASH_MAX Maximum voltage over flash LED driver
during flash event:
0000 = 300 mV
0001 = 400 mV
0010 = 500 mV
0011 = 600 mV
0100 = 700 mV
0101 = 800 mV
0110 = 900 mV
0111 = 1000 mV
1000 = 1100 mV
1001 = 1200 mV
1010 = 1300 mV
1011 = 1400 mV
1100 = 1500 mV
1101 = 1600 mV
1110 = 1700 mV
1111 = 1800 mV
ADAPT FLASH
CONTROL
[3:0]
R/W
0000
[7]
R/W
0
VAR_INPUT_SEL variable input selection:
0 = Variable D from I2C register
1 = Variable D from ADC
[6]
R/W
0
MASK_ALS_ZONE_INT
Masks the interrupt:
0 = interrupt comes from ALS zone change
1 = interrupt comes from engines
[5]
R/W
0
POWERSAVE_EN
Enable for Power-save mode:
0 = Power-save mode disabled
1 = Power-save mode enabled
0
EN_BOOST
Boost enable:
0 = Boost disabled
1= Boost enabled
0
FADE_TO_OFF
Enable group fading when device disabled:
0 = Fade_to_off disabled
1 = Fade_to_off enabled
[3]
36
R/W
FLASH_START Programmable start point for voltageover-flash LED driver during flash event:
0000 = 300 mV
0001 = 400 mV
0010 = 500 mV
0011 = 600 mV
0100 = 700 mV
0101 = 800 mV
0110 = 900 mV
0111 = 1000 mV
1000 = 1100 mV
1001 = 1200 mV
1010 = 1300 mV
1011 = 1400 mV
1100 = 1500 mV
1101 = 1600 mV
1110 = 1700 mV
1111 = 1800 mV
R/W
MISC
[2]
R/W
[1]
R/W
0
PWM_INPUT_SEL
PWM input selection which is used in dynamic backlight
calculation:
0 = Haptic generator PWM output connected to PWM
calculation unit
1 = External PWM input connected to PWM calculation
unit
[0]
R/W
0
INT_CLK_EN
Clock source selection:
1 = internal clock in use
0 = external clock in use
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Table 58. Detailed Register Descriptions (continued)
37
CHANNEL 1 PC
[5:0]
R/W
000000
Engine 1 Program Counter
38
CHANNEL 2 PC
[5:0]
R/W
000000
Engine 2 Program Counter
[7]
R
0
LED_MEAS_DONE
Bit = 1 indicates when LED TEST measurement is done.
[6]
R
0
MASK_BUSY
Mask bit for interrupt generated by ENGINE_BUSY
[5]
R
0
ALS_ZONE_CHANGE
Indicates zone change in ALS.
[4]
R
0
ENGINE_BUSY
Indicates that a lighting engine is clearing internal
registers.
[2]
R
0
CH1_INT
Interrupt for lighting engine 1.
[1]
R
0
CH2_INT
Interrupt for lighting engine 2.
INT CONFIG
[1]
R/W
0
INT_CONFIG
0 = INT enabled
1 = INT disabled, INT to general purpose ADC
PWM CONFIG
[0]
R/W
0
PWM_CONFIG
0 = PWM enabled, ENVM/TX2 disabled
1 = PWM disabled, ENVM/TX2 enabled
3C
I2C VARIABLE
[7:0]
R/W
00000000
I2C variable value
3D
RESET
[7:0]
W
00000000
Writing 11111111 into this register resets the LM8502.
[7]
R/W
0
EN_ADC
Enables general purpose ADC:
0 = general purpose ADC disabled
1 = general purpose ADC enabled
[6]
R/W
0
EN_ADC_INT
Enables interrupt from general purpose ADC:
0 = No interrupt from ADC
1 = Interrupt generated from ADC of conversion
[5]
R/W
0
CONTINUOUS_CONV
Enables continuous conversion of the ADC:
0 = Continuous conversion disabled
1= Continuous conversion enabled
3A
STATUS/INTERRUPT
3B
ADC_CTRL
Selects which signal is measured with general purpose
ADC:
00000 = LED output 1
00001 = LED output 2
00010 = LED output 3
00011 = LED output 4
00100 = LED output 5
00101 = LED output 6
00110 = LED output 7
00111 = LED output 8
01000 = LED output 9
01001 = LED output 10
01010 = Flash/Vibra output 1
01011 = Flash/Vibra output 2
01100 = Indicatior LED output
01111 = VOUT
10000 = ALS1 input
10001 = INT pin
rest not used
41
ADC CONTROL
[4:0]
R/W
00000
42
LED_TEST_ADC
[7:0]
R
00000000
Result of the LED TEST ADC.
48 – 4A
GROUP1–3 FADER
VALUE
[7:0]
R/W
00000000
Groups 1–3 fader control
4C
CH1 PROG START
ADDR
[5:0]
R/W
000000
Lighting engine 1 program start address.
4D
CH2 PROG START
ADDR
[5:0]
R/W
000000
Lighting engine 2 program start address.
50
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Table 58. Detailed Register Descriptions (continued)
4F
PROG MEM PAGE
SEL
[1:0]
R/W
00
50 – 6F
PROGRAM MEMORY
[7:0]
R/W
00000000
[7:6]
[5:3]
A0
R/W
[1:0]
[7]
FLASH BRIGHTNESS
R/W
R/W
R/W
Program memory for instructions. Every instruction is 16
bits long.
01
IND_CURRENT
Indicator LED current:
00 = 2.3 mA
01 = 4.6 mA
10 = 7.9 mA
11 = 9.2 mA
010
TORCH_CURRENT
Torch current setting per output:
000 = 18.75 mA
001 = 37.5 mA
010 = 56.25 mA
011 = 75 mA
100 = 93.75 mA
101 = 112.5 mA
110 = 131.25 mA
111 = 150 mA
TORCH BRIGHTNESS
[2]
B0
R/W
SRAM memory page selection
0
VM
Voltage mode enable:
0 = Voltage mode disabled
1= Voltage mode enabled
00
EN1–0
Flash/torch enable:
00 = Flash shutdown
01 = Indicator mode
10 = Torch mode
11 = Fash mode
0
STR
Determines how flash pulse ends:
0 = Flash pulse can be terminated by pulling STROBE
low, programming bit [1:0] of register A0H or B0H to '00'
(flash shutdown) or by allowing Flash TImeout period to
elapse.
1 = Flash pulse will only terminate by reaching the end of
Flash Timeout period.
FLASH_CURRENT per output:
0000 = 37.5 mA
0001 = 75 mA
0010 = 112.5 mA
0011 = 150 mA
0100 = 187.5 mA
0101 = 225 mA
0110 = 262.5 mA
0111 = 300mA
1000 = 337.5 mA
1001 = 375 mA
1010 = 412.5 mA
1011 = 450 mA
1100 = 487.5 mA
1101 = 525 mA
1110 = 562.5 mA
1111 = 600 mA
[6:3]
R/W
1101
[2]
R/W
0
VM Voltage mode enable:
0 = Voltage mode disabled
1= Voltage mode enabled
00
EN1–0
Flash/Torch enable:
00 = Flash shutdown
01 = Indicator mode
10 = Torch mode
11 = Flash mode
[1:0]
R/W
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Table 58. Detailed Register Descriptions (continued)
[6:5]
C0
10
FLASH DURATION
[4:0]
[7]
52
R/W
R/W
R
01111
0
CURRENT_LIMIT
Selects Flash peak current limit:
00 = 1A
01 = 1.5A
10 = 2A
11 = 2.5A
FLASH_TIMEOUT
Sets Flash timeout time:
00000 = 32 ms
00001 = 64 ms
00010 = 96 ms
00011 = 128 ms
00100 = 160 ms
00101 = 192 ms
00110 = 224 ms
00111 = 256 ms
01000 = 288 ms
01001 = 320 ms
01010 = 352 ms
01011 = 384 ms
01100 = 416 ms
01101 = 448 ms
01110 = 480 ms
01111 = 512 ms
10000 = 544 ms
10001 = 576 ms
10010 = 608 ms
10011 = 640 ms
10100 = 672 ms
10101 = 704 ms
10110 = 736 ms
10111 = 768 ms
11000 = 800 ms
11001 = 832 ms
11010 = 864 ms
11011 = 896 ms
11100 = 928 ms
11101 = 960 ms
11110 = 992 ms
11111 = 1024 ms
UVLO_FLAG
Indicates the status of VIN pin:
0 = VIN above UVLO threshold
1 = Voltage Monitor enabled and VIN falls below
programmed UVLO threshold
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Table 58. Detailed Register Descriptions (continued)
[5]
R
0
NTC FLAG
Indicates the status of NTC pin:
0 = LEDI/NTC voltage above trip point voltage V.TRIP (1V)
1 = device is active in Flash or Torch modes, it is in NTC
mode, and the voltage at LEDI/NTC has fallen below trip
point voltage VTRIP (1V).
[4]
R
0
TX2 FLAG
Indicates the status of TX2 pin:
0 = no TX event
1 = TX event since the last read of register D0H
0
TX1 FLAG
Indicates the status of TX1 pin:
0 = no TX event since the last read of register D0H
1= TX change from low to high since last read of register
D0H
[3]
D0
R
FLAG REGISTER
[2]
R
0
FLASH LED FAULT
Indicates Flash short or open fault:
0 = no open nor short in FLASH1 or FLASH2
1 = device active in Flash or Torch mode and either
FLASH1 or FLASH2 experience an open or short
condition
[1]
R
0
TSD FLAG
Indicates if Thermal Shutdown limit has been crossed:
0 = TSD limit has not been crossed
1 = TSD limit has been crossed
[0]
R
0
FLASH_TIMEOUT FLAG
Indicates if Flash timeout has expired:
0 = Flash pulse terminated before Time out
1 = Time Out expired before Flash pulse is terminated
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Table 58. Detailed Register Descriptions (continued)
[7]
[6]
E0
54
CONFIG REG 1
R/W
R/W
0
TX1/TORCH
Configuration of TX1/TORCH pin:
0 = TX1/TORCH is a power amplifier synchronization
input
1 = TX1/TORCH is a hardware Torch mode enable
1
TX2 POLARITY
Selects if TX2 is an active high or active low Flash inhibit:
0 = TX2 is an active low transmit interrupt input
1 = TX2 is an active high transmit interrupt input
[5]
R/W
0
TX2 PIN CONFIG
Configuration of TX2 pin (when PWM mode not selected
for this PWM/ENVM/TX2 pin):
0 = ENVM/TX2 pin is an active high logic input that
forces the device into Constant Voltage Output mode
1 = ENVM/TX2 pin is a power amplifier synchronization
input that forces the device from Flash mode into Torch
mode
[4]
R/W
0
NTC HYST
Hysteresis selection for NTC comparator:
0 = 125 mV hysteresis
1 = 250 mV hysteresis
[3]
R/W
0
LEDI_NTC
Configuration of LEDI/NTC pin:
0 = LEDI/NTC pin configured as LED indicator driver
1 = Indicator current source disabled and LEDI/NTC pin
configured as detector for NTC thermistor
[2]
R/W
0
DIS_EXT_STROBE
Disables/Enables STROBE input:
0 = External STROBE enabled
1 = External STROBE disabled
[1]
R/W
1
VM VALUE
Output Voltage Selection:
0 = Output voltage 4.5 V
1 = Output voltage 5 V
[0]
R/W
0
DIS PFM
Disables/Enables light load comparator:
0 = light load comparator enabled
1 = light load comparator disabled
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Table 58. Detailed Register Descriptions (continued)
[7:6]
R/W
00
UVLO_LEVEL
Selects VIN monitor threshold voltage level:
00 = 3.1V
01 = 3.2V
10 = 3.3V
11 = 3.4V
[5]
R/W
0
EN_UVLO
Disables/Enables VIN monitor:
0 = UVLO feature enabled
1 = UVLO feature disabled
0
EN_NTC_INTERRUPT
Disables/Enables possibility to send interruption in NTC
event:
0 = interrupt disabled
1 = interrupt enabled
0
UVLO_MODE
Selects Flash LED behavior in UVLO (VIN monitoring)
event:
0 = If VIN drops below UVLO threshold Flash LEDs turn
off
1 = If VIN drops below UVLO threshold Flash LEDs are
forced into Torch mode
0
AET MODE
Enables Alternative external operation:
0 = TX1/TORCH is a transmit interrupt that forces Torch
mode only during Flash event
1 = TX1/TORCH becomes dependent of STROBE
0
NTC_MODE
Selects Flash LED behavior in case of NTC event:
0 = device will be forced into Torch mode when voltage
at LEDI/NTC falls below VTRIP (1V)
1 = device will shut down flash LED current sources
when voltage at LEDI/NTC falls below VTRIP (1V)
0
TX2_SHUTDOWN
Selects Flash LED behavior in case of TX2 event:
0 = device will be forced into Torch mode in case of TX2
event
1 = device will shut down flash LED current sources in
case of TX2 event
0
ALS_ZONE_DATA
Indicates ALS zone:
000 = Zone 0
001= Zone 1
010 = Zone 2
011 = Zone 3
100 = Zone 4
[4]
[3]
F0
R/W
CONFIG REG 2
[2]
[1]
[0]
97
R/W
ALS_ZONE_DATA
[2:0]
R/W
R/W
R/W
R
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APPLICATION INFORMATION
APPLICATION DESCRIPTION
The LM8502 can be used in multiple applications. With two Flash/ Haptic outputs and 10 low-side outputs, the
LM8502 is usable in flash applications as well as in general illumination applications.
The current sink drivers provide full-scale current setting and current range up to 25.5 mA with maximum fullscale current setting. Each LED output can be powered either from VOUT or from external voltage supply. LED
outputs can be used for backlight applications as well as for fun lighting. For backlight applications the LM8502's
LED outputs may be grouped and controlled from one register; fading on and off times may be set for the group.
LED outputs can be freely grouped into one of the three groups. Two ambient light sensor inputs support the
backlight application (LED output 10 is optional) with the secondary ambient light sensing input. The incorporated
input for PWM signal enables dynamic backlight control.
For fun lighting the LM8502 offers lighting engines. Controlling outputs with engines enables flexible
programming including ramps, loops, and triggering, among others. Programmable lighting engines enable
impressive lighting sequences. Once the program is loaded into the LM8502's memory and the program started,
the device handles running of the lighting sequence, and no I2C writes are needed during execution. Engines can
be set to start with external triggering, and they can send interrupt to the MCU via INT pin.
For Flash applications the LM8502 offers an external Strobe pin, power amplifier synchronization or hardware
torch enable (TX1), as well as another power amplifier synchronization input or Voltage mode enable (TX2). The
flash driver is capable of delivering 1.2A to a single flash LED or 600 mA into two parallel LEDs. The device also
features an indicator LED to, for example, indicating flash events. A threshold detector for a negative
temperature coefficient thermistor can detect temperature near flash LEDs. Indicator and NTC are on the same
pin and alternate with each other.
When Flash driving capability is not needed, the outputs can be used, for example, to drive a vibra motor. The
LM8502 includes controls for enabling different kind of modes and PWM frequencies when driving a vibra motor.
The device also has an 8-bit register for haptic PWM control; the outputs can also be grouped or be driven from
lighting engines. When one wants to use both a vibra motor and flash on same application, two external FETs
are needed to disable the flash while running the vibra motor. This kind of application is shown in the figures
below. LED output 10 is set to control the FET status. When driving the flash haptic should be disabled.
Other features of the LM8502 include an external clock input pin, which enables efficient Power-save mode. In
Power-save mode almost all the analog blocks are shut down. Also, a general-purpose analog-to-digital
converter (ADC), which can be used, for example, to measure the LED voltages, is featured in the LM8502. This
general purpose ADC, combined with lighting engines, enables use of different sensors or audio synchronization.
Sensor or audio synchronization input can be connected to, for example, the INT pin. The value of the INT pin is
read with the general-purpose ADC. This value can be passed to the lighting engines with variables and be used
to control the lighting effects.
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2.2 PH
VIN = 2.7V TO 5.5V
10 PF
OUT
SW
D1
VDD
D2
10 PF
D3
TX1/TORCH
STROBE
D4
PWM/ENVM/TX2
D5
ALS1
D6
Main Display
D7
Interrupt
INT
External clock input for power saving
CLK
Trigger pin for lighting engine
TRIG
LM8502
D8
Sub Display
D9
D10/ALS2
VBIAS
FLASH1
SCL
FLASH2
Flash 1.2A
SDA
LEDI/NTC
EN
GND
Figure 30. LED Outputs Grouped into Main and Sub Displays
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2.2 PH
VIN = 2.7V TO 5.5V
10 PF
OUT
SW
D1
VDD
D2
10 PF
D3
TX1/TORCH
STROBE
D4
PWM/ENVM/TX2
D5
ALS1
D6
VLEDS
D7
Interrupt
INT
External clock input for power saving
CLK
Trigger pin for lighting engine
TRIG
LM8502
D8
D9
D10/ALS2
VBIAS
FLASH1
SCL
FLASH2
Flash 1.2A
SDA
LEDI/NTC
EN
GND
Figure 31. LED Outputs Partially Powered from External Voltage Supply
58
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2.2 PH
VIN = 2.7V TO 5.5V
10 PF
OUT
SW
D1
VDD
D2
10 PF
D3
TX1/TORCH
STROBE
D4
PWM/ENVM/TX2
D5
ALS1
D6
D7
Interrupt
INT
External clock input for power saving
CLK
Trigger pin for lighting engine
TRIG
LM8502
VIN
D8
D9
D10/ALS2
VBIAS
FLASH1
SCL
FLASH2
Flash 1.2A
SDA
LEDI/NTC
EN
GND
Figure 32. Two Ambient Light Sensors using Internal Resistors, One Flash LED with Thermal Sensing
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2.2 PH
VIN = 2.7V TO 5.5V
10 PF
OUT
SW
D1
VDD
D2
10 PF
D3
TX1/TORCH
STROBE
D4
PWM/ENVM/TX2
D5
ALS1
D6
VIN
D7
Interrupt
External clock input for power saving
INT
LM8502
CLK
D8
D9
D10/ALS2
Trigger pin for lighting engine
TRIG
VBIAS
FLASH1
SCL
FLASH2
Flash 1.2A
SDA
LEDI/NTC
EN
GND
Figure 33. Two Ambient Light sensors using External Resistors, One Flash LED with Thermal Sensing
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2.2 PH
VIN = 2.7V TO 5.5V
10 PF
OUT
SW
D1
VDD
D2
10 PF
D3
TX1/TORCH
STROBE
D4
PWM/ENVM/TX2
D5
ALS1
D6
LM8502
Interrupt
External clock input for power saving
D7
D8
INT
D9
CLK
D10/ALS2
Trigger pin for lighting engine
TRIG
VIBRAP
SCL
VIBRAN
SDA
M
Vibra
motor
LEDI/NTC
EN
GND
Figure 34. Vibra Motor connected to Haptic Feedback Outputs
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2.2 PH
VIN = 2.7V TO 5.5V
10 PF
OUT
SW
D1
VDD
D2
10 PF
D3
TX1/TORCH
AIN
STROBE
D4
PWM/ENVM/TX2
D5
ALS1
D6
INT
470 nF
47k
D7
LM8502
External clock input for power saving
CLK
Trigger pin for lighting engine
TRIG
D8
D9
D10/ALS2
FLASH1
SCL
VBIAS
FLASH2
Flash 1.2A
SDA
LEDI/NTC
EN
GND
Figure 35. Audio Synchronization Connection (external components needed) for
Rectifying the Audio Signal (diode) and RC-filter
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2.2 PH
10 PF
OUT
SW
D1
VDD
D2
10 PF
D3
TX1/TORCH
STROBE
D4
PWM/ENVM/TX2
D5
ALS1
D6
LM8502
D7
D8
INT
Interrupt
Pull-up resistor
D9
CLK
P channel FET
D10/ALS2
Trigger pin for
lighting engine
TRIG
VIBRAP
SCL
VIBRAN
P channel FET
SDA
LEDI/NTC
EN
M
GND
Vibra
motor
Figure 36. Flash and Vibra Motor together (two external FETs needed);
Functionality Selected with LED Output 10
APPLICATION COMPONENTS
Output Capacitor Selection
The LM8502 is designed to operate with a ceramic output capacitor of at least 4.7 µF in LED mode and a 10 µF
output capacitor in Voltage Output mode. When the boost converter is running, the output capacitor supplies the
load current during the boost converters on-time. When the NMOS switch turns off, the inductor energy is
discharged through the internal PMOS switch, thus supplying power to the load and restoring charge to the
output capacitor. This causes a sag in the output voltage during the on-time and a rise in the output voltage
during the off-time. The output capacitor is, therefore, chosen to limit the output ripple to an acceptable level
depending on load current and input/output voltage differentials and also to ensure the converter remains stable.
For proper LED operation the output capacitor must be at least 10 µF and ceramic. Larger capacitors such as a
22 µF can be used if lower output voltage ripple is desired. To estimate the output voltage ripple considering the
ripple due to capacitor discharge (ΔVQ) and the ripple due to the capacitors ESR (ΔVESR) use the following
equations:
For Continuous Conduction mode, the output voltage ripple due to the capacitor discharge is:
'VQ =
ILED x (VOUT - VIN)
fSW x VOUT x COUT
(2)
The output voltage ripple due to the output capacitors ESR is found by:
'VESR = R ESR x §
©
where
'IL =
I LED x VOUT·
VIN
¹
+ 'I L
VIN x (VOUT - VIN )
2 x f SW x L x VOUT
(3)
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In ceramic capacitors the ESR is very low so assume that 80% of the output voltage ripple is due to capacitor
discharge and 20% from ESR. Table 59 lists different manufacturers for various output capacitors and their case
sizes suitable for use with the LM8502.
Input Capacitor Selection
Choosing the correct size and type of input capacitor helps minimize the voltage ripple caused by the switching
of the LM8502’s boost converter and reduces noise on the device's input terminal that can feed through and
disrupt internal analog signals. In the Typical Application Circuits, a 10 µF ceramic input capacitor works well. It
is important to place the input capacitor as close as possible to the LM8502’s input terminals. This reduces the
series resistance and inductance that can inject noise into the device due to the input switching currents.
Table 59 lists various input capacitors that or recommended for use with the LM8502.
Table 59. Recommended Input/Output Capacitors (X5R Dielectric)
Manufacturer
Part Number
Value
Case Size
Voltage Rating
TDK Corporation
C1608JB0J106M
10 µF
0603(1.6mm×0.8mm×0.8mm)
6.3V
TDK Corporation
C2012JB1A106M
10 µF
0805(2mm×1.25mm×1.25mm)
10V
TDK Corporation
C2012JB0J226M
22 µF
0805(2mm×1.25mm×1.25mm)
6.3V
Murata
GRM21BR61A106KE19
10 µF
0805(2mm×1.25mm×1.25mm)
10V
Murata
GRM21BR60J226ME39L
22 µF
0805(2mm×1.25mm×1.25mm)
6.3V
Inductor Selection
The LM8502 is designed to use a 2.2 µH inductor. Table 60 lists various inductors and their manufacturers that
can work well with the LM8502. When the device is boosting (VOUT > VIN) the inductor will typically be the biggest
area of efficiency loss in the circuit. Therefore, choosing an inductor with the lowest possible series resistance is
important. Additionally, the saturation rating of the inductor should be greater than the maximum operating peak
current of the LM8502. This prevents excess efficiency loss that can occur with inductors that operate in
saturation and prevents overheating of the inductor and possible damage. For proper inductor operation and
circuit performance ensure that the inductor saturation and the peak current limit setting of the LM8502 is greater
than IPEAK. IPEAK can be calculated by:
I LOAD VOUT
VIN x (VOUT - VIN)
IPEAK =
K
x
VIN
+ 'IL where
'IL =
2 x f SW x L x VOUT
(4)
ƒSW = 2MHz, and efficiency can be found in the Typical Performance Characteristics plots.
Table 60. Recommended Inductors
Manufacturer
L
Part Number
Dimensions (L×W×H)
ISAT
Coilcraft
2.2 µH
LPS3015–222
3mm×3mm×1.2mm
2.3A
TDK
2.2 µH
VLS252012T-2R2M1R3
2mm×2.5mm×1.2mm
1.5A
NTC Thermistor Selection
NTC thermistors have a temperature to resistance relationship of:
E
R(T) = R25°C x e
§ 1 - 1·
©T °C+ 273 298¹
(5)
where β is given in the thermistor datasheet and R25°C is the thermistors value at +25°C. R3 in Figure 38 is
chosen so that it is equal to:
R3 =
RT( TRIP) (VBIAS - VTRIP )
VTRIP
(6)
where R(T)TRIP is the thermistor's value at the temperature trip point, VBIAS is shown in Figure 37, and VTRIP = 1V
(typ.). Choosing R3 here gives a more linear response around the temperature trip voltage. For example, with
VBIAS = 2.5V, a thermistor whose nominal value at +25°C is 100 kΩ, and a β = 4500K, the trip point is chosen to
be +93°C. The value of R(T) at 93°C is:
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E
R3 is then:
º
»
¼
R(T) = 100 k : x e
º
1
- 1 »
93 + 273 298 ¼
= 6.047 k :
6.047 k: x (2.5 V - 1V)
= 9 .071 k:
1V
(7)
Figure 37 shows the linearity of the thermistor resistive divider of the previous example. With the internal
hysteresis set to 125 mV the comparator output will trip and turn the Flash current back on if the thermistor
temperature drops to approximately +86°C.
1.5
VBIAS = 2.5V,
RTHERMISTOR = 100 k:
@ +25°C, B = 4500,
R3 = 9 k:
1.4
1.3
V LEDI/NTC (V)
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
70
75
80
85
90
95
100 105 110
TEMPERATURE (°C)
Figure 37. Thermistor Resistive Divider Response vs Temperature
Another useful equation for the thermistor resistive divider is developed by combining the equations for R3, and
R(T) and solving for temperature. This gives the following relationship.
T( °C) =
298°C x LN
E x 298°C
VTRIP x R3
(VBIAS - VTRIP) x R25 °C
273°C
+E
(8)
Using a spreadsheet such as Excel, different curves for the temperature trip point T(°C) can be created vs R3,
Beta, or VBIAS in order to better help choose the thermal components for practical values of thermistors, series
resistors (R3) or reference voltages for VBIAS.
Programming bit [3] of Configuration Register 1 with a '1' selects Thermal Comparator mode making the
LEDI/NTC pin a comparator input for flash LED thermal sensing. Figure 38 shows the internal block diagram of
the thermal-sensing circuit which is OR’d with both the TX1 and ENVM/TX2 (TX2 mode) to force the LM8502
from Flash to Torch mode. This is intended to prevent LED overheating during flash pulses. In NTC mode the
internal comparator has a selectable 125 mV or 250 mV hysteresis (see Configuration Register 1, Bit [4]).
The termination of the thermistor must be done directly to the cathode of the Flash LED. This will provide the
best thermal coupling (lowest thermal resistance). Consequently, with the thermistor tied to the LED's cathode,
the thermistor's return can potentially see large GND currents.
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65
LM8502
SNVS592D – OCTOBER 2009 – REVISED FEBRUARY 2013
www.ti.com
Internal to LM8502
TX2
TX1/
TORCH
Force Torch or
LED Shutdown (TX2 or NTC only)
VBIAS
1V
R3
R(T)
+
LEDI/NTC
125 mV Hysteresis, Configuration Register 1 bit [4] = 0
250 mV Hysteresis, Configuration Register 1 bit [4] = 1
Figure 38. Thermistor Voltage Divider and Sensing Circuit
Layout Recommendations
The high frequency and large switching currents of the LM8502 make the choice of layout important. The
following steps should be used as a reference to ensure the device is stable and maintains proper voltage and
current regulation across its intended operating voltage and current range.
1. Place CIN as close as possible to the VIN terminal and the GND terminal.
2. Place COUT as close as possible to the OUT terminal and the GND terminal. The returns for both CIN and
COUT should come together at one point, and as close to the GND pin as possible. This will reduce the series
inductance and limit noise at the GND pin that will inject noise into the device.
66
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Product Folder Links: LM8502
LM8502
www.ti.com
SNVS592D – OCTOBER 2009 – REVISED FEBRUARY 2013
REVISION HISTORY
Changes from Revision C (February 2013) to Revision D
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 66
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67
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM8502TME/NOPB
ACTIVE
DSBGA
YFQ
30
250
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-30 to 85
8502
LM8502TMX/NOPB
ACTIVE
DSBGA
YFQ
30
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-30 to 85
8502
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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