Product
Folder
Sample &
Buy
Technical
Documents
Support &
Community
Tools &
Software
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
LM36923 Highly Efficient Triple-String White LED Driver
1 Features
3 Description
•
The LM36923 is an ultra-compact, highly efficient,
threestring white-LED driver designed for LCD display
backlighting. The device can power up to 8 series
LEDs at up to 25 mA per string. An adaptive current
regulation method allows for different LED voltages in
each string while maintaining current regulation.
1
•
•
•
•
•
•
•
•
•
•
•
1% Matched Current Sinks Across (Process,
Voltage, Temp)
3% Current Sink Accuracy Across (Process,
Voltage, Temp)
11-Bit Dimming Resolution
Up to 91.6% Solution Efficiency
Drives from One to Three Parallel LED Strings at
up to 28 V
PWM Dimming Input
I2C Programmable
Selectable 500-kHz and 1-MHz Switching
Frequency with Optional –12% shift
Auto Switch Frequency Mode (250 kHz, 500 kHz,
1 MHz)
Four Configurable Overvoltage Protection
Thresholds (17 V, 21 V, 25 V, 29 V)
Four Configurable Overcurrent Protection
Thresholds (750 mA, 1000 mA, 1250 mA, 1500
mA)
Thermal Shutdown Protection
The LED current is adjusted via an I2C interface or
through a logic level PWM input. The PWM duty cycle
is internally sensed and mapped to an 11-bit current
thus allowing for a wide range of PWM frequencies
and noise-free operation.
The device operates over the 2.5-V to 5.5-V input
voltage range and -40°C to 85°C temperature range.
Device Information(1)
PART NUMBER
LM36923
PACKAGE
DSBGA (12)
BODY SIZE (MAX)
1.755 mm × 1.355 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
space
space
space
2 Applications
Power Source for Smart Phone and Tablet
Backlighting
space
space
space
Simplified Schematic
Typical String-to-String Matching vs LED Current
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
4
4
4
4
5
6
7
Absolute Maximum Ratings .....................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information .................................................
Electrical Characteristics...........................................
I2C Timing Requirements..........................................
Typical Characteristics ..............................................
Detailed Description ............................................ 10
7.1
7.2
7.3
7.4
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
10
10
11
16
7.5 Programming........................................................... 25
7.6 Register Maps ........................................................ 26
8
Applications and Implementation ...................... 29
8.1 Application Information............................................ 29
8.2 Typical Application .................................................. 29
9
Power Supply Recommendations...................... 37
9.1 Input Supply Bypassing .......................................... 37
10 Layout................................................................... 37
10.1 Layout Guidelines ................................................. 37
10.2 Layout Example .................................................... 40
11 Device and Documentation Support ................. 41
11.1
11.2
11.3
11.4
11.5
11.6
Device Support......................................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
41
41
41
41
41
41
12 Mechanical, Packaging, and Orderable
Information ........................................................... 41
4 Revision History
Changes from Original (March 2015) to Revision A
Page
•
Changed pin name "VOUT" to "OUT" .................................................................................................................................... 3
•
Changed pin name in Layout Example from 'VOUT' to 'OUT' ............................................................................................. 39
2
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
5 Pin Configuration and Functions
YFF Package
12-Pin DSBGA
Top View
A
LED1
ASEL
GND
B
LED2
SDA
SW
C
LED3
SCL
OUT
D
PWM
HWEN
IN
1
2
3
Pin Functions
PIN
I/O
DESCRIPTION
NUMBER
NAME
A1
LED1
Input
Input to current sink 1. The boost converter regulates the minimum voltage between
LED1, LED2, LED3 to VHR.
A2
BL_ADJ
Input
LED current adjust input. When BL_ADJ is driven to a logic high voltage the LED current
steps down to the programmed low current value.
A3
GND
Input
Ground
B1
LED2
Input
Input pin to current sink 2. The boost converter regulates the minimum voltage between
LED1, LED2 ,LED3 to VHR.
B2
SDA
I/O
B3
SW
Output
C1
LED3
Input
Input pin to current sink 3. The boost converter regulates the minimum voltage between
LED1, LED2, LED3 to VHR.
C2
SCL
Input
Clock Input for I2C-compatible interface.
C3
OUT
Input
OUT serves as the sense point for overvoltage protection. Connect OUT to the positive
pin of the output capacitor.
D1
PWM
Input
Logic level input for PWM current control.
D2
HWEN
Input
Hardware enable input. Drive HWEN high to bring the device out of shutdown and allow
I2C writes or PWM control.
D3
IN
Input
Input voltage connection. Bypass IN to GND with a minimum 2.2-µF ceramic capacitor.
Data I/O for I2C-Compatible Interface.
Drain Connection for internal low side NFET, and anode connection for external Schottky
diode.
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
3
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
MIN
MAX
UNIT
IN
Input voltage
–0.3
6
V
OUT
Output overvoltage sense input
–0.3
30
V
SW
Inductor connection
–0.3
30
V
LED1, LED2, LED3
LED string cathode connection
–0.3
30
V
HWEN, PWM, SDA,
SCL, BL_ADJ
Logic I/Os
–0.3
6
V
150
°C
150
°C
Maximum junction temperature, TJ_MAX
Storage temperature, Tstg
(1)
–65
Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating
conditions is not implied. Exposure to absolute–maximum–rated conditions for extended periods may affect device reliability.
6.2 ESD Ratings
VALUE
Electrostatic
discharge
V(ESD)
(1)
(2)
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001
(1)
±2000
Charged-device model (CDM), per JEDEC specification JESD22-C101 (2)
±500
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. Pins listed as ±2000
V may actually have higher performance.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process. Pins listed as ±500 V
may actually have higher performance.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
MAX
UNIT
IN
Input voltage
2.5
5.5
V
OUT
Overvoltage sense input
0
29.5
V
SW
Inductor connection
0
29.5
V
LED1, LED2, LED3
LED string cathode connection
0
29.5
V
HWEN, PWM, SDA,
SCL, BL_ADJ
Logic I/Os
0
5.5
V
6.4 Thermal Information
THERMAL METRIC (1)
YFQ (DSBGA)
12 PINS
RθJA
Junction-to-ambient thermal resistance
RθJC(top)
Junction-to-case (top) thermal resistance
0.7
RθJB
Junction-to-board thermal resistance
43.9
ΨθJT
Junction-to-top characterization parameter
2.9
ΨθJB
Junction-to-board characterization parameter
43.7
(1)
4
UNIT
88.9
°C/W
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics.
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
6.5 Electrical Characteristics
Limits apply over the full operating ambient temperature range (−40°C ≤ TA ≤ 85°C) and VIN = 3.6 V, typical values are at TA =
25°C (unless otherwise noted).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
–1%
0.1%
1%
UNIT
BOOST
(1)
LED current matching ILED1 to
ILED2 to ILED3
50 µA ≤ ILED ≤ 25 mA, 2.7 V ≤ VIN ≤ 5 V
(linear or exponential mode)
Accuracy
Absolute Accuracy (ILED1,
ILED2, ILED3)
50 µA ≤ ILED ≤ 25 mA, 2.7 V ≤ VIN ≤ 5 V
(linear or exponential mode)
ILED_MIN
Minimum LED current (per
string)
IMATCH
–3%
PWM or I2C current control (linear or
exponential mode)
0.1%
50
µA
25
mA
1/3
(0.3%)
LSB
ILED_MAX
Maximum LED current (per
string)
RDNL
IDAC ratio-metric DNL
VHR
Regulated current sink
headroom voltage
ILED = 25 mA
210
ILED = 5 mA
100
VHR_MIN
Current sink minimum
headroom voltage
ILED = 95% of nominal, ILED = 5 mA
Efficiency
Typical efficiency
VIN = 3.7 V, ILED = 5 mA/string, Typical
Application circuit (3x7 LEDs), (POUT/PIN)
87%
RNMOS
NMOS switch on resistance
ISW = 250 mA
0.25
ICL
NMOS switch current limit
VOVP
Output overvoltage protection
exponential mode only
2.7 V ≤ VIN ≤ 5 V
ON threshold, 2.7 V ≤ VIN
≤5V
35
50
Switching frequency
DMAX
Maximum boost duty cycle
Shutdown current
2.7 V ≤ VIN ≤ 5 V, boost
frequency
shift = 0
575
750
875
OCP = 01
860
1000
1110
OCP = 10
1100
1250
1400
OCP = 11
1350
1500
1650
OVP = 00
16
17
17.5
OVP = 01
20
21
21.5
OVP = 10
24
25
25.5
OVP = 11
28
29
29.5
Boost frequency
select = 0
Boost frequency
select = 1
500
525
950
1000
1050
92%
94%
1.2
Thermal shutdown
5
135
Hysteresis
mA
V
V
475
Chip enable bit = 0, SDA = SCL = IN or GND,
2.7 V ≤ VIN ≤ 5 V
mV
Ω
0.5
ƒSW
TSD
mV
OCP = 00
OVP
Hysteresis
ISHDN
3%
kHz
µA
°C
15
PWM INPUT
Min ƒPWM
50
Max ƒPWM
tMIN_ON
tMIN_OFF
(1)
Sample rate = 24 MHz
Minimum pulse ON time
Minimum pulse OFF time
50
Hz
kHz
Sample rate = 24 MHz
183.3
Sample rate = 4 MHz
1100
Sample rate = 800 kHz
5500
Sample rate = 24 MHz
183.3
Sample rate = 4 MHz
1100
Sample rate = 800 kHz
5500
ns
ns
LED Current Matching between strings is given as the worst case matching between any two strings. Matching is calculated as ((ILEDX –
ILEDY)/(ILEDX + ILEDY) × 100.
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
5
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
Electrical Characteristics (continued)
Limits apply over the full operating ambient temperature range (−40°C ≤ TA ≤ 85°C) and VIN = 3.6 V, typical values are at TA =
25°C (unless otherwise noted).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
3.5
5
ms
11
bits
tSTART-UP
Turn-on delay from shutdown
to backlight on
PWM input active, PWM = logic high,HWEN
input from low to high, ƒPWM = 10 kHz (50%
duty cycle)
PWMRES
PWM input resolution
1.6 kHz ≤ ƒPWM ≤ 12 kHz, PWM hysteresis =
00, PWM sample rate = 11
VIH
Input logic high
HWEN, BL_ADJ, SCL, SDA, PWM inputs
1.25
VIN
VIL
Input logic low
HWEN, BL_ADJ, SCL, SDA, PWM inputs
0
0.4
PWM pulse filter = 00
tGLITCH
PWM input glitch rejection
tPWM_STBY
PWM shutdown period
0
15
PWM pulse filter = 01
60
100
140
PWM pulse filter = 10
90
150
210
PWM pulse filter = 11
120
200
280
Sample rate = 24 MHz
0.54
0.6
0.66
Sample rate = 4 MHz
2.7
3
3.3
22.5
25
27.5
Sample rate = 800 kHz
UNIT
V
ns
ms
6.6 I2C Timing Requirements
MIN
TYP
MAX
UNIT
t1
SCL clock period
2.5
µs
t2
Data in setup time to SCL high
100
ns
t3
Data out stable after SCL low
0
ns
t4
SDA low Setup Time to SCL low (start)
100
ns
t5
SDA high hold time after SCL high (stop)
100
ns
t1
SCL
t5
t4
SDA_IN
t2
SDA_OUT
t3
2
Figure 1. I C Timing
6
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
6.7 Typical Characteristics
17.2
0.54
17.1
17.0
OVP THRESHOLD (V)
OVP HYSTERESIS (V)
0.535
0.53
0.525
-40 degC
0.52
30 degC
MAX -40 degC
MIN -40 degC
MAX 30 degC
MIN 30 degC
MAX 125 degC
MIN 125 degC
16.9
16.8
16.7
16.6
16.5
16.4
16.3
125 degC
16.2
MAX 125 degC
MIN 125 degC
25.1
25.0
24.9
OVP THRESHOLD (V)
OVP THRESHOLD (V)
MIN 30 degC
20.6
20.5
20.4
MIN 30 degC
MAX 125 degC
MIN 125 degC
24.6
24.5
24.4
24.3
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
2.50
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
24.1
2.50
24.2
VIN (V)
C001
Figure 4. 21-V OVP Threshold
C001
Figure 5. 25-V OVP Threshold
MAX -40 degC
MIN -40 degC
MAX 30 degC
MIN 30 degC
MAX 125 degC
MIN 125 degC
0.5
0.45
0.4
28.8
RDSON (Ohms)
OVP THRESHOLD (V)
MIN -40 degC
MAX 30 degC
24.7
20.2
VIN (V)
MAX -40 degC
24.8
20.3
28.7
28.6
28.5
28.4
0.35
0.3
0.25
0.2
0.15
28.3
0.1
125 degC
28.2
0.05
30 degC
28.1
0
-40 degC
5.50
5.25
5.00
VIN (V)
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
C001
2.75
2.50
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
2.50
VIN (V)
5.50
5.25
5.00
4.75
4.50
4.25
MIN -40 degC
MAX 30 degC
20.7
28.9
4.00
MAX -40 degC
20.8
29.0
C001
Figure 3. 17-V OVP Threshold
20.9
29.1
3.75
21.0
3.50
21.1
3.25
VIN (V)
C001
Figure 2. OVP Hysteresis
21.2
3.00
VIN (V)
2.75
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
2.50
2.50
0.515
C001
Figure 7. RDSON
Figure 6. 29-V OVP Threshold
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
7
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
Typical Characteristics (continued)
3
2.5
2
2
SWITCHING IQ (mA)
ISHDN (uA)
2.5
1.5
1
-40 degC
30 degC
125 degC
0.5
0
1.5
1
0.5
-40 degC
30 degC
125 degC
0
214
0.77
212
0.76
PEAK CURRENT (A)
VHR_MIN (mV)
0.78
210
208
206
204
125 degC
30 degC
-40 degC
-40 degC
30 degC
125 degC
0.75
0.74
0.73
0.72
0.71
0.70
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
2.50
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
2.50
VIN (V)
VIN (V)
C001
ILED = 25 mA
C001
Open Loop
Figure 10. VHR MIN
1.03
Figure 11. 750-mA OCP Current
1.30
-40 degC
30 degC
125 degC
1.02
-40 degC
30 degC
125 degC
1.29
1.28
1.01
1.27
PEAK CURRENT (A)
PEAK CURRENT (A)
5.50
5.25
5.00
4.75
4.50
C001
No Load
Figure 9. IQ Current (Switching)
216
200
4.25
fSW= 1 Mhz
202
4.00
3.75
3.50
3.25
3.00
VIN (V)
C001
Figure 8. Shutdown Current
1.00
0.99
0.98
0.97
1.26
1.25
1.24
1.23
1.22
1.21
0.96
1.20
VIN (V)
C001
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
2.50
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
2.50
VIN (V)
Open Loop
C001
Open Loop
Figure 12. 1000-mA OCP Current
8
2.75
2.50
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
2.50
VIN (V)
HWEN = GND
Submit Documentation Feedback
Figure 13. 1250-mA OCP Current
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
Typical Characteristics (continued)
1.55
-40 degC
1.54
30 degC
1.53
125 degC
PEAK CURRENT (A)
1.52
1.51
1.50
1.49
1.48
1.47
1.46
1.45
1.44
1.43
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
2.50
VIN (V)
C001
Open Loop
Figure 14. 1500-mA OCP Current
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
9
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
7 Detailed Description
7.1 Overview
The LM36923 is an inductive boost plus 3 current sink white-LED driver designed for powering from one to three
strings of white LEDs used in display backlighting. The device operates over the 2.5-V to 5.5-V input voltage
range. The 11-bit LED current is set via an I2C interface, via a logic level PWM input, or a combination of both.
7.2 Functional Block Diagram
SW
Overvoltage
Protection
17 V
21 V
25 V
29 V
IN
HWEN
OUT
OVP
0.25 W
Fault Detection
Overvoltage
LED String Short
LED String Open
Current Limit
Thermal
Shutdown
LED
Fault
BL_ADJ
Thermal
Shutdown
135oC
TSD
OCP
Boost Control
Boost Switching
Frequency
1 MHz
887 kHz
500 kHz
443 kHz
250 kHz
220 kHz
Auto
Frequency
Mode
Force Low
Current Target
Boost Current
Limit
750 mA
1500 mA
SDA
I2C Interface
Min Headroom
Select
SCL
Adaptive
Headroom
Current Sinks
LED1
PWM Sample
Rate
800 kHz
4 MHz
24 MHz
PWM
PWM Sampler
11-Bit
Brightness
Code
LED Current Ramping
No ramp
0.125 ms/step
0.25 ms/step
0.5 ms/step
1 ms/step
2 ms/step
4 ms/step
8 ms/step
16 ms/step
LED Current
Mapping
Exponential
Linear
LED2
LED3
LED String
Enables
GND
10
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
7.3 Feature Description
7.3.1 Enabling the LM36923
The LM36923 has a logic level input HWEN which serves as the master enable/disable for the device. When
HWEN is low the device is disabled, the registers are reset to their default state, the I2C bus is inactive, and the
device is placed in a low-power shutdown mode. When HWEN is forced high the device is enabled, and I2C
writes are allowed to the device.
7.3.1.1 Current Sink Enable
Each current sink in the device has a separate enable input. This allows for a 1-string, 2-string, or 3-string
application. The default is with three strings enabled. Once the correct LED string configuration is programmed,
the device can be enabled by writing the chip enable bit high (register 0x10 bit[0]), and then either enabling PWM
and driving PWM high, or writing a non-zero code to the brightness registers.
The default setting for the device is with the chip enable bit set to 1, PWM input enabled, and the device in linear
mapped mode. Therefore, on power up once HWEN is driven high, the device enters the standby state and
actively monitors the PWM input. After a non-zero PWM duty cycle is detected the LM36923 converts the duty
cycle information to the linearly weighted 11-bit brightness code. This allows for operation of the device in a
stand-alone configuration without the need for any I2C writes. Figure 15 and Figure 16 describe the start-up
timing for operation with both PWM controlled current and with I2C controlled current.
VIN
HWEN
PWM
ILED
tHWEN_PWM
tPWM_DAC
tDD_LED
tDAC_LED
tPWM_STBY
Figure 15. Enabling the LM36923 via PWM
VIN
HWEN
I2C
I2C Registers In
Reset
I2C Data Valid
I2C Brightness
Data Sent
ILED
tHWEN_I2C
tBRT_DAC
tDAC_LED
Figure 16. Enabling the LM36923 via I2C
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
11
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
Feature Description (continued)
7.3.2 LM36923 Start-Up
The LM36923 can be enabled or disabled in various ways. When disabled, the device is considered shutdown,
and the quiescent current drops to ISHDN. When the device is in standby, it returns to the ISHDN current level
retaining all programmed register values. Table 1 describes the different operating states for the LM36923.
Table 1. LM36923 Operating Modes
2
PWM INPUT
I C
BRIGHTNESS
REGISTERS
0x18 bits[2:0]
0x19 bits[7:0]
BRIGHTNESS
MODE
0x11 bits[6:5]
DEVICE
ENABLE
0x10 bit[0]
XXX
X
XXX
XX
0
Off, device disabled
0
X
XXX
XX
1
Off, device standby
At least one
enabled
X
0
00
1
Off, device in standby
At least one
enabled
X
Code > 000
00
1
+.'& = 50J# × 1.003040572%K@A +.'& = 37.806ä# +12.195ä# × %K@A
At least one
enabled
0
XXX
01
1
At least one
enabled
PWM Signal
XXX
01
1
At least one
enabled
0
XXX
10 or 11
1
At least one
enabled
X
0
10 or 11
1
At least one
enabled
PWM Signal
Code > 000
10 or 11
1
LED STRING
ENABLES
0x10 bits[3:1]
(1)
LED CURRENT
(EXP MAPPING)
0x11 bit[7] = 1
(LIN MAPPING)
0x11 bit[7] = 0
See (1)
See (1)
Off, device in standby
+.'& = 50J# × 1.003040572%K@A +.'& = 37.806ä# +12.195ä# × %K@A
See (1)
See (1)
Off, device in standby
Off, device in standby
+.'& = 50J# × 1.003040572%K@A +.'& = 37.806ä# +12.195ä# × %K@A
See (1)
See (1)
Code is the 11-bit code output from the ramper (see Figure 21, Figure 23, Figure 25, Figure 27). This can be the I2C brightness code,
the converted PWM duty cycle or the 11-bit product of both.
7.3.3 Brightness Mapping
There are two different ways to map the brightness code (or PWM duty cycle) to the LED current: linear and
exponential mapping.
7.3.3.1 Linear Mapping
For linear mapped mode the LED current increases proportionally to the 11-bit brightness code and follows the
relationship:
+.'& = 37.806ä# +12.195ä# × %K@A
(1)
This is valid from codes 1 to 2047. Code 0 programs 0 current. Code is an 11-bit code that can be the I2C
brightness code, the digitized PWM duty cycle, or the product of the two.
7.3.3.2 Exponential Mapping
In exponential mapped mode the LED current follows the relationship:
+.'& = 50J# × 1.003040572%K@A
(2)
This results in an LED current step size of approximately 0.304% per code. This is valid for codes from 1 to
2047. Code 0 programs 0 current. Code is an 11-bit code that can be the I2C brightness code, the digitized PWM
duty cycle, or the product of the two. Figure 17 details the LED current exponential response.
The 11-bit (0.304%) per code step is small enough such that the transition from one code to the next in terms of
LED brightness is not distinguishable to the eye. This therefore gives a perfectly smooth brightness increase
between adjacent codes.
12
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
LED Current (mA)
25
2.5
0.25
0.025
0
256
512
768
1024
1280
1536
1792
11 Bit Brightness Code
2048
C006
Figure 17. LED Current vs Brightness Code (Exponential Mapping)
7.3.4 PWM Input
The PWM input is a sampled input which converts the input duty cycle information into an 11-bit brightness code.
The use of a sampled input eliminates any noise and current ripple that traditional PWM controlled LED drivers
are susceptible to.
The PWM input uses logic level thresholds with VIH_MIN = 1.25 V and VIL_MAX = 0.4 V. Since this is a sampled
input, there are limits on the max PWM input frequency as well as the resolution that can be achieved.
7.3.4.1 PWM Sample Frequency
There are four selectable sample rates for the PWM input. The choice of sample rate depends on three factors:
1. Required PWM Resolution (input duty cycle to brightness code, with 11 bits max)
2. PWM Input Frequency
3. Efficiency
7.3.4.1.1 PWM Resolution and Input Frequency Range
The PWM input frequency range is 50 Hz to 50 kHz. To achieve the full 11-bit maximum resolution of PWM duty
cycle to the LED brightness code (BRT), the input PWM duty cycle must be ≥ 11 bits, and the PWM sample
period (1/ƒSAMPLE) must be smaller than the minimum PWM input pulse width. Figure 18 shows the possible
brightness code resolutions based on the input PWM frequency. The minimum PWM frequency for each PWM
sample rate is described in PWM Timeout.
12
24MHz
4MHz
800kHz
Maximum Achievable Resolution (bits)
11
10
9
8
7
6
0.1kHz
1.0kHz
10.0kHz
Input PWM Frequency
C001
Figure 18. PWM Sample Rate, Resolution, and PWM Input Frequency
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
13
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
7.3.4.1.2 PWM Sample Rate and Efficiency
Efficiency is maximized when the lowest ƒSAMPLE is chosen since this lowers the quiescent operating current of
the device. Table 2 describes the typical efficiency tradeoffs for the different sample clock settings.
Table 2. PWM Sample Rate Trade-Offs
PWM SAMPLE RATE
(ƒSAMPLE)
TYPICAL INPUT CURRENT, DEVICE ENABLED
ILED = 10 mA/string, 2 x 7 LEDs
TYPICAL EFFICIENCY
(0x12 Bits[7:6])
ƒSW = 1 MHz
VIN = 3.7 V
0
1.03 mA
90.7%
1
1.05 mA
90.6%
1X
1.35 mA
90.4%
7.3.4.1.2.1 PWM Sample Rate Example
The number of bits of resolution on the PWM input varies according to the PWM Sample rate and PWM input
frequency.
Table 3. PWM Resolution vs PWM Sample Rate
PWM
FREQUENCY
(kHz)
RESOLUTION
(PWM SAMPLE RATE = 800 kHz)
RESOLUTION
(PWM SAMPLE RATE = 4 MHz)
RESOLUTION
(PWM SAMPLE RATE = 24 MHz)
0.4
11
11
11
2
8.6
11
11
12
6.1
8.4
11
7.3.4.2 PWM Hysteresis
To prevent jitter at the input PWM signal from feeding through the PWM path and causing oscillations in the LED
current, the LM36923 offers 7 selectable hysteresis settings. The hysteresis works by forcing a specific number
of 11-bit LSB code transitions to occur in the input duty cycle before the LED current changes. Table 4 describes
the hysteresis. The hysteresis only applies during the change in direction of brightness currents. Once the
change in direction has taken place, the PWM input must over come the required LSB(s) of the hysteresis setting
before the brightness change takes effect. Once the initial hysteresis has been overcome and the direction in
brightness change remains the same, the PWM to current response changes with no hysteresis.
Table 4. PWM Input Hysteresis
HYSTERESIS SETTING
(0x12 Bits[4:2])
MIN CHANGE IN PWM
PULSE WIDTH (Δt)
REQUIRED TO CHANGE
LED CURRENT, AFTER
DIRECTION CHANGE
(for fPWM < 11.7 kHz)
MIN CHANGE IN PWM
DUTY CYCLE (ΔD)
REQUIRED TO CHANGE
LED CURRENT AFTER
DIRECTION CHANGE
EXPONENTIAL MODE
LINEAR MODE
000 (0 LSB)
1/(fPWM × 2047)
0.05%
0.30%
0.05%
14
MIN (ΔILED), INCREASE FOR INITIAL CODE
CHANGE
001 (1 LSB)
1/(fPWM × 1023)
0.10%
0.61%
0.10%
010 (2 LSBs)
1/(fPWM × 511)
0.20%
1.21%
0.20%
011 (3 LSBs)
1/(fPWM × 255)
0.39%
2.40%
0.39%
100 (4 LSBs)
1/(fPWM × 127)
0.78%
4.74%
0.78%
101 (5 LSBs)
1/(fPWM × 63)
1.56%
9.26%
1.56%
110 (6 LSBs)
1/(fPWM × 31)
3.12%
17.66%
3.12%
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
tJITTER
tJITTER
D/fPWM
1/fPWM
x
x
x
D is tJITTER x fPWM or equal to #/6%¶V = ¨' [ 2048 codes.
For 11-bit resolution, #LSBs is equal to a hysteresis setting of LN(#/6%¶V)/LN(2).
For example, with a tJITTER of 1 µs and a fPWM of 5 kHz, the hysteresis setting should be:
LN(1 µ s x 5 kHz x 2048)/LN(2) = 3.35 (4 LSBs).
Figure 19. PWM Hysteresis Example
7.3.4.3 PWM Step Response
The LED current response due to a step change in the PWM input is approximately 2 ms to go from minimum
LED current to maximum LED current.
7.3.4.4 PWM Timeout
The LM36923 PWM timeout feature turns off the boost output when the PWM is enabled and there is no PWM
pulse detected. The timeout duration changes based on the PWM Sample Rate selected which results in a
minimum supported PWM input frequency. The sample rate, timeout, and minimum supported PWM frequency
are summarized in Table 5.
Table 5. PWM Timeout and Minimum Supported PWM Frequency vs PWM Sample Rate
MINIMUM SUPPORTED PWM
FREQUENCY
SAMPLE RATE
TIMEOUT
0.8 MHz
25 msec
48 Hz
4 MHz
3 msec
400 Hz
24 MHz
0.6 msec
2000 Hz
7.3.5 LED Current Ramping
There are 8 programmable ramp rates available in the LM36923. These ramp rates are programmable as a time
per step. Therefore, the ramp time from one current set-point to the next, depends on the number of code steps
between currents and the programmed time per step. This ramp time to change from one brightness set-point
(Code A) to the next brightness set-point (Code B) is given by:
¿P = 4=IL_N=PA × :%K@A $ F%K@A# F1;
(3)
For example, assume the ramp is enabled and set to 1 ms per step. Additionally, the brightness code is set to
0x444 (1092d). Then the brightness code is adjusted to 0x7FF (2047d). The time the current takes to ramp from
the initial set-point to max brightness is:
(4)
1IO
¿P =
× :0T7(( F 0T444 F 1; = 954IO
OPAL
(5)
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
15
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
7.3.6 Regulated Headroom Voltage
REGULATED HEADROOM VOLTAGE (V)
In order to optimize efficiency, current accuracy, and string-to-string matching the LED current sink regulated
headroom voltage (VHR) varies with the target LED current. Figure 20 details the typical variation of VHR with
LED current. This allows for increased solution efficiency as the dropout voltage of the LED driver changes.
Furthermore, in order to ensure that both current sinks remain in regulation whenever there is a mismatch in
string voltages, the minimum headroom voltage between VLED1, VLED2, VLED3 becomes the regulation point
for the boost converter. For example, if the LEDs connected to LED1 require 12 V, the LEDs connected to LED2
require 12.5 V , and the LEDs connected to LED3 require 13 V at the programmed current, then the voltage at
LED1 is VHR + 1 V, the voltage at LED2 is VHR + 0.5 V, and the voltage at LED3 is regulated at VHR. In other
words, the boost makes the cathode of the highest voltage LED string the regulation point.
240
220
200
180
160
140
120
100
80
50.0
5.0
0.5
0.1
LED Current (mA)
C001
Figure 20. LM36923 Typical Exponential Regulated Headroom Voltage vs Programmed LED Current
7.4 Device Functional Modes
Device Functional Modes describes the different operating modes and features available within the LM36923.
7.4.1 Brightness Control Modes
The LM36923 has 4 brightness control modes:
1. I2C Only (brightness mode 00)
2. PWM Only (brightness mode 01)
3. I2C × PWM with ramping only between I2C codes (brightness mode 10)
4. I2C × PWM with ramping between I2C × PWM changes (brightness mode 11)
7.4.1.1 I2C Only (Brightness Mode 00)
In brightness control mode 00 the I2C Brightness registers are in control of the LED current, and the PWM input
is disabled. The brightness data (BRT) is the concatenation of the two brightness registers (3 LSBs) and (8
MSBs) (registers 0x18 and 0x19, respectively). The LED current only changes when the MSBs are written,
meaning that to do a full 11-bit current change via I2C, first the 3 LSBs are written and then the 8 MSBs are
written. In this mode the ramper only controls the time from one I2C brightness set-point to the next Figure 21.
16
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
Device Functional Modes (continued)
VOUT
Boost
Digital Domain
Analog Domain
Min VHR
RAMP_RATE Bits
ILED1
ILED2
ILED3
Driver_1
BRT Code = I2C
Code
I2C Brightness Reg
DACi
Ramper
Mapper
Driver_2
DAC
Driver_3
MAP_MODE
RAMP_EN
Figure 21. Brightness Control 00 (I2C Only)
ILED_t1
Ramp Rate
tRAMP
ILED_t0
t0
t1
1.
At time t0 the I2C Brightness Code is changed from 0x444 (1092d) to 0x7FF (2047d)
2.
Ramp Rate programmed to 1ms/step
3.
Mapping Mode set to Linear
4.
ILED_t0 = 1092 × 12.213 µA = 13.337 mA
5.
ILED_t1 = 2047 × 12.213 µA = 25 mA
6.
tRAMP = (t1 – t0) = 1ms/step × (2047 – 1092 – 1) = 954 ms
Figure 22. I2C Brightness Mode 00 Example (Ramp Between I2C Code Changes)
7.4.1.2 PWM Only (Brightness Mode 01)
In brightness mode 01, only the PWM input sets the brightness. The I2C code is ignored. The LM36923 samples
the PWM input, determines the duty cycle and this measured duty cycle is translated into an 11-bit digital code.
The resultant code is then applied to the internal ramper (see Figure 23).
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
17
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
Device Functional Modes (continued)
VOUT
Boost
Digital Domain
Analog Domain
Min VHR
ILED1
RAMP_RATE Bits
ILED2
ILED3
Driver_1
BRT Code =
2047 × Duty Cycle
DACi
PWM Input
PWM Detector
Ramper
Mapper
RAMP_EN
MAP_MODE
DAC
Driver_2
Driver_3
Figure 23. Brightness Control 01 (PWM Only)
ILED_t1
Ramp Rate
tRAMP
ILED_t0
t0
t1
1.
At time t0 the PWM duty cycle changed from 25% to 100%
2.
Ramp Rate programmed to 1 ms/step
3.
Mapping Mode set to Linear
4.
ILED_t0 = 25 mA × 0.25 = 6.25 mA
5.
ILED_t1 = 25 mA × 1 = 25 mA
6.
tRAMP = (t1 – t0) = 1ms/step × (2047 × 1 – 2047 × 0.25 – 1) = 1534 ms
Figure 24. Brightness Control Mode 01 Example (Ramp Between Duty Cycle Changes)
7.4.1.3 I2C + PWM Brightness Control (Multiply Then Ramp) Brightness Mode 10
In brightness control mode 10 the I2C Brightness register and the PWM input are both in control of the LED
current. In this case the I2C brightness code is multiplied with the PWM duty cycle to produce an 11-bit code
which is then sent to the ramper. In this mode ramping is achieved between I2C x PWM currents (see Figure 25).
18
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
Device Functional Modes (continued)
VOUT
Digital Domain
Analog Domain
Boost
Min VHR
RAMP_RATE Bits
ILED1
I2C Brightness Reg
Ramper
ILED2
ILED3
Driver_1
BRT Code =
I2C × Duty Cycle
DACi
Mapper
Driver_2
DAC
Driver_3
RAMP_EN
PWM
Detector
PWM Input
MAP_MODE
Figure 25. Brightness Control 10 (I2C + PWM)
ILED_t1
Ramp Rate
tRAMP
ILED_t0
t0
t1
1.
At time t0 the I2C Brightness code changed from 0x444 (1092d) to 0x7FF (2047d)
2.
At time t0 the PWM duty cycle changed from 50% to 75%
3.
Ramp Rate programmed to 1ms/step
4.
Mapping Mode set to Linear
5.
ILED_t0 = 1092 × 12.213 µA × 0.5 = 6.668 mA
6.
ILED_t1 = 2047 × 12.213 µA × 0.75 = 18.75 mA
7.
tRAMP = (t1 – t0) = 1ms/step × (2047 × 0.75 – 1092 × 0.5 – 1) = 988 ms
Figure 26. Brightness Control Mode 10 Example (Multiply Duty Cycle then Ramp)
7.4.1.4 I2C + PWM Brightness Control (Ramp Then Multiply) Brightness Mode 11
In brightness control mode 11 both the I2C brightness code and the PWM duty cycle control the LED current. In
this case the ramper only changes the time from one I2C brightness code to the next. The PWM duty cycle is
multiplied with the I2C brightness code at the output of the ramper (see Figure 27).
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
19
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
Device Functional Modes (continued)
VOUT
Boost
Digital Domain
Analog Domain
Min VHR
RAMP_RATE Bits
ILED1
ILED2
ILED3
Driver_1
BRT Code =
I2C × Duty Cycle
I2C Brightness Reg
DACi
Ramper
Mapper
RAMP_EN
MAP_MODE
DAC
Driver_2
Driver_3
PWM Input
PWM Detector
Figure 27. Brightness Control 11 (I2C + PWM)
ILED_t1
ILED_t0+
Ramp
Rate
ILED_t0-
tRAMP
t0
t1
1.
At time t0 the I2C Brightness code changed from 0x444 (1092d) to 0x7FF (2047d)
2.
At time t0 the PWM duty cycle changed from 50% to 75%
3.
Ramp Rate programmed to 1 ms/step
4.
Mapping Mode set to Linear
5.
ILED_t0– = 1092 × 12.213 µA × 0.5 = 6.668 mA
6.
ILED_t0+ = 1092 × 12.213 µA × 0.75 = 10.002 mA
7.
tRAMP = (t1 – t0) = 1 ms/step × (2047 – 1092 – 1) = 954 ms
Figure 28. Brightness Control Mode 11 Example (Ramp Current Then Multiply Duty Cycle)
7.4.2 Boost Switching Frequency
The LM36923 has two programmable switching frequencies: 500 kHz and 1 MHz. These are set via the Boost
Control 1 register 0x13 bit [5]. Once the switching frequency is set, this nominal value can be shifted down by
12% via the boost switching frequency shift bit (register 0x13 bit[6]). Operation at 500 kHz is better suited for
configurations which use a 22-µH inductor. Operation at 1 MHz is primarily beneficial when using a 10-µH
inductor and where efficiency at maximum load current is more important. For maximum efficiency across the
entire load current range the device incorporates an automatic frequency shift mode (see Auto Switching
Frequency).
20
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
Device Functional Modes (continued)
7.4.2.1 Minimum Inductor Select
The LM36923 can use inductors in the range of 10 µH to 22 µH. In order to optimize the converter response to
changes in VIN and load, the Min Inductor Select bit (register 0x13 bit[4]) should be selected depending on which
value of inductance is chosen. For 22-µH inductors this bit should be set to 1. For less than 22 µH, this bit should
be set to 0.
7.4.3 Auto Switching Frequency
To take advantage of frequency vs load dependent losses, the LM36923 has the ability to automatically change
the boost switching frequency based on the magnitude of the load current. In addition to the register
programmable switching frequencies of 500 kHz and 1 MHz, the auto-frequency mode also incorporates a low
frequency selection of 250 kHz. It is important to note that the 250-kHz frequency is only accessible in autofrequency mode and has a maximum boost duty cycle (DMAX) of 50%.
Auto-frequency mode operates by using 2 programmable registers (Auto Frequency High Threshold (register
0x15) and Auto Frequency Low Threshold (0x16)). The high threshold determines the switchover from 1 MHz to
500 kHz. The low threshold determines the switchover from 500 kHz to 250 kHz. Both the High and Low
Threshold registers take an 8-bit code which is compared against the 8 MSB of the brightness register (register
0x19). Table 6 details the boundaries for this mode.
Table 6. Auto Switching Frequency Operation
BRIGHTNESS CODE MSBs (Register 0x19 bits[7:0])
BOOST SWITCHING FREQUENCY
< Auto Frequency Low Threshold (register 15 Bits[7:0])
250 kHz (DMAX = 50%)
> Auto Frequency Low Threshold (Register 15 Bits[7:0]) or < Auto
Frequency High Threshold (Register 14 Bits[7:0])
500 kHz
≥ Auto Frequency High Threshold (register 14 Bits[7:0])
1 MHz
Automatic-frequency mode is enabled whenever there is a non-zero code in either the Auto-Frequency High or
Auto-Frequency Low registers. To disable the auto-frequency shift mode, set both registers to 0x00. When
automatic-frequency select mode is disabled, the switching frequency operates at the programmed frequency
(Register 0x13 bit[5]) across the entire LED current range. Table 7 provides a guideline for selecting the auto
frequency 250-kHz threshold setting, the actual setting needs to be verified in the application.
Table 7. Auto Frequency 250-kHz Threshold Settings
CONDITION
(Vf=3.2 V,
ILED=25 mA)
INDUCTOR
(µH)
RECOMMENDED AUTO FREQUENCY
LOW THRESHOLD MAXIMUM VALUE
(NO SHIFT)
OUTPUT POWER AT AUTO
FREQUENCY SWITCHOVER
(W)
3 × 4 LEDs
10
0x17
0.079
3 × 5 LEDs
10
0x15
0.089
3 × 6 LEDs
10
0x13
0.097
3 × 7 LEDs
10
0x11
0.101
3 × 8 LEDs
10
0x0f
0.102
7.4.4 Backlight Adjust Input (BL_ADJ)
Driving BL_ADJ to a logic high voltage provides a way to quickly reduce the LED current during system highpower conditions such as camera flash, PA transmit, or other high battery-current conditions. The adjusted
current target is programmable via register 0x17 bits[7:0]. Only the MSBs of the brightness code are adjustable.
Additionally, the BL_ADJ input only decreases the current from the initial target. If the initial target is > the
adjusted current then nothing happens — the LED current remains at its current value. Figure 30 details the
BL_ADJ operation.
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
21
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
VOUT
Boost
Digital Domain
Analog Domain
Min VHR
ILED1
BRT Code
(I2C and/or PWM)
11
ILED3
DACi
Mapper
Backlight Adjust
Threshold [10:3] +
3 /6%¶V VHW WR 000
ILED2
Driver_1
11
DAC
Driver_2
11
Driver_3
MAP_MODE
BL_ADJ
Active High/
Active Low
Polarity Bit
Figure 29. Backlight Adjust Operation
BL_ADJ
ILED_BRT
ILED
ILED_ADJ
tDAC_LED
tBRT_DAC
tBRT_DAC
LED Current operates at an initial target ILED_BRT which is set by either I2C or PWM (or both).
When the BL_ADJ input is driven to a logic high the LM36923's brightness code at the Mapper input has the MSBs
set to the BL_ADJ Threshold and the LSBs set to 000.
ILED steps down to the new target current in < 50 µs.
When BL_ADJ is forced low the LED current returns to the initial brightness target.
Figure 30. Backlight Adjust Timing
7.4.4.1 Back-Light Adjust Input Polarity
The BL_ADJ input can have either active high or active low polarity. With active high polarity (default), driving the
BL_ADJ input high forces the LED current to the BL_ADJ low target current. With active low polarity, driving the
BL_ADJ input low forces the LED current to the BL_ADJ low target current. The polarity is set via bit 0 in register
11.
22
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
7.4.5 Fault Protection/Detection
7.4.5.1 Overvoltage Protection (OVP)
The LM36923 provides four OVP thresholds (17 V, 21 V, 25 V, and 29 V). The OVP circuitry monitors the boost
output voltage (VOUT) and protects OUT and SW from exceeding safe operating voltages in case of open load
conditions or in the event the LED string voltage requires more voltage than the programmed OVP setting. The
OVP thresholds are programmed in register 13 bits[3:2]. The operation of OVP differentiates between two
overvoltage conditions and responds differently as outlined below:
7.4.5.1.1 Case 1 OVP Fault Only (OVP Threshold Hit and All Enabled Current Sink Inputs > 40 mV)
In steady-state operation with VOUT near the OVP threshold a rapid change in VIN or brightness code can result in
a momentary transient excursion of VOUT above the OVP threshold. In this case the boost circuitry is disabled
until VOUT drops below OVP – hysteresis (1 V). Once this happens the boost is re-enabled and steady state
regulation continues. If VOUT remains above the OVP threshold for > 1 ms the OVP Flag is set (register 0x1F
bit[0]).
7.4.5.1.2 Case 2a OVP Fault and Open LED String Fault (OVP Threshold Occurrence and Any Enabled Current Sink
Input ≤ 40 mV)
When any of the enabled LED strings is open the boost converter tries to drive VOUT above OVP and at the same
time the open string(s) current sink headroom voltage(s) (LED1, LED2, LED3) drop to 0. When the LM36923
detects three occurrences of VOUT > OVP and any enabled current sink input (VLED1 or VLED2, VLED3) ≤ 40 mV,
the OVP Fault flag is set (register 0x1F bit[0]), and the LED Open Fault flag is set (register 0x1F bit[4]).
7.4.5.1.3 Case 2b OVP Fault and Open LED String Fault (OVP Threshold Duration and Any Enabled Current Sink
Input ≤ 40 mV)
When any of the enabled LED strings is open the boost converter tries to drive VOUT above OVP and at the same
time the open string(s) current sink headroom voltage(s) (LED1, LED2, LED3) drop to 0. When the LM36923
detects VOUT > OVP for > 1 msec and any enabled current sink input (VLED1 or VLED2, VLED3) ≤ 40 mV, the OVP
Fault flag is set (register 0x1F bit[0]), and the LED Open Fault flag is set (register 0x1F bit[4]).
7.4.5.1.4 OVP/LED Open Fault Shutdown
The LM36923 has the option of shutting down the device when the OVP flag is set. This option can be enabled
or disabled via register 0x1E bit[0]. When the shutdown option is disabled the fault flag is a report only. When the
device is shut down due to an OVP/LED String Open fault, the fault flags register must be read back before the
LM36923 can be re-enabled.
7.4.5.1.5 Testing for LED String Open
The procedure for detecting an open in a LED string is:
• Apply power the the LM36923.
• Enable all LED strings (Register 0x10 = 0x0F).
• Set maximum brightness (Register 0x18 = 0x07 and Register 0x19 = 0xFF).
• Set the brightness control (Register 0x11 = 0x00).
• Open LED1 string.
• Wait 4 msec.
• Read LED open fault (Register 0x1F).
• If bit[4] = 1, then a LED open fault condition has been detected.
• Connect LED1 string.
• Repeat the procedure for the other LED strings.
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
23
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
7.4.5.2 LED String Short Fault
The LM36923 can detect an LED string short fault. This happens when the voltage between VIN and any enabled
current sink input has dropped below (1.5 V). This test can only be performed on one LED string at a time.
Performing this test with more than one LED string enabled can result in a faulty reading. The procedure for
detecting a short in a LED string is:
• Apply power the the LM36923.
• Enable only LED1 string (Register 0x10 = 0x03).
• Enable short fault (Register 0x1E = 0x01.
• Set maximum brightness (Register 0x18 = 0x07 and Register 0x19 = 0xFF).
• Set the brightness control (Register 0x11 = 0x00).
• Wait 4 msec.
• Read LED short fault (Register 0x1F).
• If bit[3] = 1, then a LED short fault condition has been detected.
• Set chip enable and LED string enable low (Register 0x10 = 0x00).
• Repeat the procedure for the other LED strings.
7.4.5.3 Overcurrent Protection (OCP)
The LM36923 has 4 selectable OCP thresholds (750 mA, 1000 mA, 1250 mA, and 1500 mA). These are
programmable in register 0x13 bits[1:0]. The OCP threshold is a cycle-by-cycle current limit and is detected in
the internal low-side NFET. Once the threshold is hit the NFET turns off for the remainder of the switching period.
7.4.5.3.1 OCP Fault
If enough overcurrent threshold events occur, the OCP Flag (register 0x1F bit[1]) is set. To avoid transient
conditions from inadvertently setting the OCP Flag, a pulse density counter monitors OCP threshold events over
a 128-µs period. If 8 consecutive 128-µs periods occur where the pulse density count has found 2 or more OCP
events,then the OCP Flag is set.
During device start-up and during brightness code changes, there is a 4-ms blank time where OCP events are
ignored. As a result, if the device starts up in an overcurrent condition there is an approximate 5-ms delay before
the OCP Flag is set.
7.4.5.3.2 OCP Shutdown
The LM36923 has the option of shutting down the device when the OCP flag is set. This option can be enabled
or disabled via register 0x1E bit[1]. When the shutdown option is disabled, the fault flag is a report only. When
the device is shut down due to an OCP fault, the fault flags register must be read back before the LM36923 can
be re-enabled.
7.4.5.4 Device Overtemperature (TSD)
Thermal shutdown (TSD) is triggered when the device die temperature reaches 135˚C. When this happens the
boost stops switching, and the TSD Flag (register 0x1F bit[2]) is set. The boost automatically starts up again
when the die temperature cools down to 120˚C.
7.4.5.4.1 Overtemperature Shutdown
The LM36923 has the option of shutting down the device when the TSD flag is set. This option can be enabled
or disabled via register 0x1E bit[2]. When the shutdown option is disabled the fault flag is a report only. When the
device is shutdown due to a TSD fault, the Fault Flags register must be read back before the LM36923 can be
re-enabled.
24
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
7.5 Programming
7.5.1 I2C Interface
7.5.1.1 Start and Stop Conditions
The LM36923 is configured via an I2C interface. START (S) and STOP (P) conditions classify the beginning and
the end of the I2C session Figure 31. A START condition is defined as SDA transitioning 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. The I2C bus is considered busy after a
START condition and free after a STOP condition. During the data transmission the I2C master can generate
repeated START conditions. A START and a repeated START conditions 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.
SDA
SCL
S
P
Start Condition
Stop Condition
Figure 31. I2C Start and Stop Conditions
7.5.1.2 I2C Address
The 7-bit chip address for the LM36923 is (0x36). After the START condition the I2C master sends the 7-bit chip
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 chip address selects the register address to which the data is written. The
third byte contains the data for the selected register.
7.5.1.3 Transferring Data
Every byte on the SDA line must be eight bits long with the most significant bit (MSB) transferred first. Each byte
of data must be followed by an acknowledge bit (ACK). The acknowledge related clock pulse, (9th clock pulse),
is generated by the master. The master then releases SDA (HIGH) during the 9th clock pulse. The LM36923
pulls down SDA during the 9th clock pulse, signifying an acknowledge. An acknowledge is generated after each
byte has been received.
7.5.1.4 Register Programming
For glitch free operation, the following bits and/or registers should only be programmed while the LED Enable
bits are 0 (Register 0x10, Bit [3:1] = 0) and Device Enable bit is 1 (Register 0x10, Bit[0] = 1) :
1. Register 0x11 Bit[7] (Mapping Mode)
2. Register 0x11 Bits[6:5] (Brightness Mode)
3. Register 0x11 Bit[4] (Ramp Enable)
4. Register 0x11 Bit[3:1] (Ramp Rate)
5. Register 0x12 Bits[7:6] (PWM Sample Rate)
6. Register 0x12 Bits[5] (PWM Polarity)
7. Register 0x12 Bit[3:2] (PWM Hysteresis)
8. Register 0x12 Bit[3:2] (PWM Pulse Filter)
9. Register 0x15 (auto frequency high threshold)
10. Register 0x16 (auto frequency low threshold)
11. Register 0x17 (back-light adjust threshold)
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
25
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
7.6 Register Maps
Note: Read of Reserved (R) or Write Only register returns 0
Table 8. Revision (0x00)
Bits [7:4]
Bits [3:0]
R
Revision Code
Table 9. Software Reset (0x01)
Software Reset
Bit [0]
Bits [7:1]
R
0 = Normal Operation
1 = Device Reset (automatically resets back to 0)
Table 10. Enable (0x10)
LED2
Enable
Bit [2]
LED3 Enable
Bit [3]
Bits [7:4]
R
0 = Disabled
1 = Enabled
(Default)
LED1
Enable
Bit [1]
Device
Enable
Bit [0]
0=
0=
0=
Disabled
Disabled
Disabled
1 = Enabled 1 = Enabled 1 = Enabled
(Default)
(Default)
(Default)
NOTE: When the Device Enable (Bit [0]) is set high the following registers/bits are set to the default value: Register 0x11 Bit[0], Register
0x12 Bits[7:0].
Table 11. Brightness Control (0x11)
Mapping Mode
Bit [7]
0 = Linear (default)
1 = Exponential
Brightness
Mode
Bits [6:5]
00 = Brightness
Register Only
01 = PWM Duty
Cycle Only
10 = Multiply
Then Ramp
(Brightness
Register ×
PWM)
11 = Ramp
Then Multiply
(Brightness
Register ×
PWM) (default)
Ramp Enable
Bits [4]
Ramp Rate
Bit [3:1]
0 = Ramp Disabled (default)
1 = Ramp Enabled
000 = 0.125
ms/step
(default)
001 = 0.250
ms/step
010 = 0.5
ms/step
011 = 1
ms/step
100 = 2
ms/step
101 = 4
ms/step
110 = 8
ms/step
111 = 16
ms/step
BL_ADJ
Polarity
Bits [0]
0 = Active
Low
1 = Active
High
(default)
Table 12. PWM Control (0x12)
26
PWM Sample Rate
Bit [7:6]
PWM Input
Polarity
Bit [5]
00 = 800 kHz
01 = 4 MHz (default)
1X = 24 MHz
0 = Active Low
1 = Active High
(default)
PWM Hysteresis
Bits [4:2]
000 = None
001 = 1 LSB
010 = 2 LSBs
011 = 3 LSBs
100 = 4 LSBs (default)
101 = 5 LSBs
110 = 6 LSBs
111 = N/A
Submit Documentation Feedback
PWM Pulse Filter
Bit [1:0]
00 = No Filter
01 = 100 ns
10 = 150 ns
11 = 200 ns (default)
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
Table 13. Boost Control 1 (0x13)
Reserved
Bit [7]
N/A
Boost Switching
Frequency Shift
Bit [6]
Boost Switching Frequency
Select
Bit [5]
0 = –12% Shift
1 =No Shift (default)
0 = 500 kHz
1 = 1 MHz (default)
Minimum
Inductor
Select
Bit [4]
Overvoltage
Protection
(OVP)
Bits [3:2]
Current Limit
(OCP)
Bits [1:0]
0 = 10 µH
(default)
1 = 22 µH
00 = 17 V
01 = 21 V
10 = 25 V
11 = 29 V
(default)
00 = 750 mA
01 = 1000 mA
10 = 1250 mA
11 = 1500 mA
(default)
Table 14. Auto Frequency High Threshold (0x15)
Auto Frequency High Threshold (500 kHz to 1000 kHz)
Bits [7:0]
Compared against the 8 MSBs of 11-bit brightness code (default = 00000000).
Table 15. Auto Frequency Low Threshold (0x16)
Auto Frequency High Threshold (250 kHz to 500 kHz)
Bits [7:0]
Compared against the 8 MSBs of 11-bit brightness code (default = 00000000).
Table 16. Back Light Adjust Threshold (0x17)
Back Light Adjust Threshold (Brightness Ceiling)
Bits [7:0]
When BL_ADJ Input is driven high the MSBs of the brightness code are forced to the code in this register (default = 00000000).
Table 17. Brightness Register LSBs (0x18)
Bits [7:3]
I2C Brightness Code (LSB)
Bits [2:0]
R
This is the lower 3 bits of the 11-bit brightness code (default = 111).
Table 18. Brightness Register MSBs (0x19)
I2C Brightness Code (MSB)
Bits [7:0]
This is the upper 8 bits of the 11-bit brightness code (default = 11111111).
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
27
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
Table 19. Fault Control (0x1E)
Reserved
Bits [7:4]
R
LED Short
Fault Enable
Bit [3]
0 = LED Short
Fault Detection
is disabled
(default)
1 = LED Short
Fault Detection
is enabled
TSD Shutdown Disable
Bit [2]
0 = When the TSD Flag is set,
the device is forced into
shutdown.
1 = No shutdown (default)
OCP
Shutdown
Disable
Bit [1]
0 = When the
OCP Flag is
set, the device
is forced into
shutdown.
1 = No
shutdown
(default)
OVP/LED
Open
Shutdown
Disable
Bit [0]
0 = When
the OVP
Flag is set,
the device
is forced
into
shutdown.
1 = No
shutdown
(default)
Table 20. Fault Flags (0x1F)
Reserved
Bits [7:5]
R
28
LED Open
Fault
Bit [4]
LED Short
Fault
Bit [3]
TSD Fault
Bit [2]
OCP Fault
Bit [1]
1 = LED
String Open
Fault
1 = LED
Short Fault
1 = Thermal Shutdown
Fault
1 = Current Limit
Fault
Submit Documentation Feedback
OVP
Fault
Bit [0]
1=
Output
Overvolta
ge Fault
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
8 Applications and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LM36923 provides a complete high-performance LED lighting solution for mobile handsets. The LM36923 is
highly configurable and can support multiple LED configurations.
8.2 Typical Application
Figure 32. LM36923 Typical Application
8.2.1 Design Requirements
DESIGN PARAMETER
EXAMPLE VALUE
Minimum input voltage (VIN)
2.7 V
LED parallel/series configuration
3×5
LED maximum forward voltage (Vf)
3.2 V
Efficiency
82%
The number of LED strings, number of series LEDs, and minimum input voltage are needed in order to calculate
the peak input current. This information guides the designer to make the appropriate inductor selection for the
application. The LM36923 boost converter output voltage (VOUT) is calculated as follows: number of series LEDs
× Vƒ + 0.23 V. The LM36923 boost converter output current (IOUT) is calculated as follows: number of parallel
LED strings × 25 mA. The LM36923 peak input current is calculated using Equation 6.
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
29
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
8.2.2 Detailed Design Procedure
Table 21. Typical Application Component List
CONFIGURATION
L1
D1
COUT
3p7s, 3p8s
VLF504012MT-100M
VLF504012MT-150M
NSR0530P2T5G
C2012X7R1H105K085AC
3p6s
VLF504012MT-220M
NSR0530P2T5G
C2012X7R1H105K085AC
3p5s
VLF403210MT-100M
NSR0530P2T5G
C2012X7R1H105K085AC
3p4s
VLF302510MT-100M
NSR0530P2T5G
C2012X7R1H105K085AC
8.2.2.1 Component Selection
8.2.2.1.1 Inductor
The LM36923 requires a typical inductance in the range of 10 µH to 22 µH. When selecting the inductor, ensure
that the saturation rating for the inductor is high enough to accommodate the peak inductor current of the
application (IPEAK) given in the inductor datasheet. The peak inductor current occurs at the maximum load
current, the maximum output voltage, the minimum input voltage, and the minimum switching frequency setting.
Also, the peak current requirement increases with decreasing efficiency. IPEAK can be estimated using
Equation 6:
+2'#- =
8176 × +176
8+0
8+0 × K
+
× l1 +
p
8+0 × K
2 × B59 × .
8176
(6)
Also, the peak current calculated above is different from the peak inductor current setting (ISAT). The NMOS
switch current limit setting (ICL_MIN) must be greater than IPEAK from Equation 6 above.
8.2.2.1.2 Output Capacitor
The LM36923 requires a ceramic capacitor with a minimum of 0.4 µF of capacitance at the output, specified over
the entire range of operation. This ensures that the device remains stable and oscillation free. The 0.4 µF of
capacitance is the minimum amount of capacitance, which is different than the value of capacitor. Capacitance
would take into account tolerance, temperature, and DC voltage shift.
Table 22 lists possible output capacitors that can be used with the LM36923. Figure 33 shows the DC bias of the
four TDK capacitors. The useful voltage range is determined from the effective output voltage range for a given
capacitor as determined by Equation 7:
&% 8KHP=CA &AN=PEJC R
0.38µ(
:1 F 6KH; × :1 F 6AIL_?K;
(7)
Table 22. Recommended Output Capacitors
NOMINAL
CAPACITANCE
(µF)
TOLERANCE (%)
TEMPERATURE
COEFFICIENT (%)
RECOMMENDED MAX
OUTPUT VOLTAGE
(FOR SINGLE
CAPACITOR)
50
1
±10
±15
22
50
2.2
±10
±15
24
0603
35
2.2
±10
±15
12
0603
50
1
±10
±15
15
PART NUMBER
MANUFACTURER
CASE
SIZE
VOLTAGE
RATING (V)
C2012X5R1H105K085AB
TDK
0805
C2012X5R1H225K085AB
TDK
0805
C1608X5R1V225K080AC
TDK
C1608X5R1H105K080AB
TDK
For example, with a 10% tolerance, and a 15% temperature coefficient, the DC voltage derating must be ≥
0.38/(0.9 × 0.85) = 0.5 µF. For the C1608X5R1H225K080AB (0603, 50-V) device, the useful voltage range
occurs up to the point where the DC bias derating falls below 0.523 µF, or around 12 V. For configurations where
VOUT is > 15 V, two of these capacitors can be paralleled, or a larger capacitor such as the
C2012X5R1H105K085AB must be used.
30
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
Capacitance (µF)
www.ti.com
2
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
C2012X5R1H105K085AB
C2012X5R1H225K085AB
C1608X5R1V225K080AC
C1608X5R1H105K080AB
0
2
4
6
8
10
12
14
16
18
20
22
24
26
DC Bias
28
C006
Figure 33. DC Bias Derating for 0805 Case Size and
0603 Case Size 35-V and 50-V Ceramic Capacitors
8.2.2.1.3 Input Capacitor
The input capacitor in a boost is not as critical as the output capacitor. The input capacitor primary function is to
filter the switching supply currents at the device input and to filter the inductor current ripple at the input of the
inductor. The recommended input capacitor is a 2.2-µF ceramic (0402, 10-V device) or equivalent.
8.2.3 Application Curves
L1 = 10 µH (VLF403212-100M) or 22 µH (VLF504015-220M) as noted in graphs, D1 = NSR530P2T5G, LEDs are Rohm
SML312WBCW1, temperature = 25°C, VIN = 3.7 V, unless otherwise noted.
Two String, AF Enabled, 10 uH, 3.7V
95%
90%
90%
85%
85%
BOOST EFFICIENCY
BOOST EFFICIENCY
Three String, AF Enabled, 10 uH, 3.7V
95%
80%
75%
3p4s
3p5s
70%
3p6s
65%
3p7s
3p8s
60%
75%
2p4s
2p5s
70%
2p6s
65%
2p7s
2p8s
60%
60
50
40
30
20
LED CURRENT (mA)
C001
Figure 34. Boost Efficiency vs Series LEDs
10
0
80
70
60
50
40
30
20
10
0
LED CURRENT (mA)
80%
C001
Figure 35. Boost Efficiency vs Series LEDs
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
31
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
L1 = 10 µH (VLF403212-100M) or 22 µH (VLF504015-220M) as noted in graphs, D1 = NSR530P2T5G, LEDs are Rohm
SML312WBCW1, temperature = 25°C, VIN = 3.7 V, unless otherwise noted.
Two String, AF Enabled -12%, 10 uH, 3.7V
95%
90%
90%
85%
85%
BOOST EFFICIENCY
BOOST EFFICIENCY
Three String, AF Enabled -12%, 10 uH, 3.7V
95%
80%
75%
3p4s
3p5s
70%
3p6s
65%
3p7s
3p8s
60%
BOOST EFFICIENCY
BOOST EFFICIENCY
3p4s
80%
2p8s
75%
2p7s
2p6s
70%
2p5s
2p4s
BOOST EFFICIENCY
85%
3p5s
3p4s
Two String, 500kHz, 22 uH, 3.7V
80%
2p8s
75%
2p7s
2p6s
70%
2p5s
2p4s
65%
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
LED CURRENT (mA)
C001
Figure 40. Boost Efficiency vs Series LEDs
50
85%
3p6s
40
90%
3p7s
30
90%
3p8s
C001
Figure 39. Boost Efficiency vs Series LEDs
95%
80%
20
10
0
80
70
60
50
40
30
20
10
0
LED CURRENT (mA)
Three String, 500kHz, 22 uH, 3.7V
LED CURRENT (mA)
Two String, 443kHz, 22 uH, 3.7V
C001
Figure 38. Boost Efficiency vs Series LEDs
65%
C001
65%
LED CURRENT (mA)
60
3p5s
50
3p6s
40
3p7s
30
3p8s
20
80%
70%
10
0
80
70
60
50
40
30
20
10
0
85%
75%
2p8s
95%
85%
95%
2p7s
Figure 37. Boost Efficiency vs Series LEDs
90%
65%
BOOST EFFICIENCY
2p6s
65%
90%
70%
2p5s
LED CURRENT (mA)
Three String, 443kHz, 22 uH, 3.7V
75%
2p4s
70%
C001
Figure 36. Boost Efficiency vs Series LEDs
32
75%
60%
LED CURRENT (mA)
95%
80%
C001
Figure 41. Boost Efficiency vs Series LEDs
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
L1 = 10 µH (VLF403212-100M) or 22 µH (VLF504015-220M) as noted in graphs, D1 = NSR530P2T5G, LEDs are Rohm
SML312WBCW1, temperature = 25°C, VIN = 3.7 V, unless otherwise noted.
Three String, 887kHz, 22 uH, 3.7V
90%
90%
85%
85%
80%
3p8s
75%
3p7s
3p6s
70%
3p5s
3p4s
65%
BOOST EFFICIENCY
3p6s
3p7s
3p8s
80%
75%
2p5s
2p6s
65%
2p7s
2p8s
BOOST EFFICIENCY
3p8s
Two String, 887kHz, 10 uH, 3.7V
80%
75%
2p4s
2p5s
70%
2p6s
65%
2p7s
2p8s
60%
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
LED CURRENT (mA)
C001
Figure 46. Boost Efficiency vs Series LEDs
60
85%
3p7s
50
85%
3p6s
40
90%
3p5s
30
90%
3p4s
C001
Figure 45. Boost Efficiency vs Series LEDs
95%
80%
20
10
0
80
70
60
50
40
30
20
10
0
LED CURRENT (mA)
Three String, 887kHz, 10 uH, 3.7V
LED CURRENT (mA)
2p4s
70%
95%
60%
Two String, 1Mhz, 10 uH, 3.7V
C001
Figure 44. Boost Efficiency vs Series LEDs
65%
C001
60%
LED CURRENT (mA)
50
3p5s
40
3p4s
30
85%
80%
20
85%
70%
10
0
90%
75%
2p4s
LED CURRENT (mA)
90%
60%
2p5s
Figure 43. Boost Efficiency vs Series LEDs
95%
65%
2p6s
70%
95%
70%
2p7s
C001
Three String, 1Mhz, 10 uH, 3.7V
BOOST EFFICIENCY
2p8s
75%
80
70
60
50
40
30
20
10
0
LED CURRENT (mA)
BOOST EFFICIENCY
80%
65%
Figure 42. Boost Efficiency vs Series LEDs
75%
Two String, 887kHz, 22 uH, 3.7V
95%
BOOST EFFICIENCY
BOOST EFFICIENCY
95%
C001
Figure 47. Boost Efficiency vs Series LEDs
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
33
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
L1 = 10 µH (VLF403212-100M) or 22 µH (VLF504015-220M) as noted in graphs, D1 = NSR530P2T5G, LEDs are Rohm
SML312WBCW1, temperature = 25°C, VIN = 3.7 V, unless otherwise noted.
95%
90%
90%
85%
85%
BOOST EFFICIENCY
BOOST EFFICIENCY
Three String, 500kHz, 10 uH, 3.7V
95%
80%
75%
3p4s
3p5s
70%
3p6s
65%
3p7s
3p8s
75%
2p6s
65%
BOOST EFFICIENCY
3p7s
3p8s
C001
Two String, 443kHz, 10 uH, 3.7V
80%
75%
2p4s
2p5s
70%
2p6s
65%
2p7s
2p8s
60%
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
LED CURRENT (mA)
60
85%
3p6s
50
85%
3p5s
40
90%
3p4s
30
90%
80%
20
10
80
70
60
50
40
30
20
10
0
95%
60%
2p8s
LED CURRENT (mA)
Three String, 443kHz, 10 uH, 3.7V
65%
2p7s
Figure 49. Boost Efficiency vs Series LEDs
95%
70%
2p5s
C001
Figure 48. Boost Efficiency vs Series LEDs
75%
2p4s
70%
60%
LED CURRENT (mA)
BOOST EFFICIENCY
80%
0
60%
Two String, 500kHz, 10 uH, 3.7V
LED CURRENT (mA)
C001
C001
Figure 51. Boost Efficiency vs Series LEDs
Figure 50. Boost Efficiency vs Series LEDs
100
25
Exponential
Linear
23
20
18
LED CURRENT (mA)
CURRENT (mA)
10
1
0.1
15
13
10
8
5
3
0
2048
1792
1536
1280
1024
768
34
BRIGHTNESS CODE
C001
Figure 52. LED Current vs Brightness Code (Exponential
Mapping)
512
BRIGHTNESS CODE
256
2048
1920
1792
1664
1536
1408
1280
1152
1024
896
768
640
512
384
256
128
0
0
0.01
C001
Figure 53. LED Current vs Brightness Code
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
L1 = 10 µH (VLF403212-100M) or 22 µH (VLF504015-220M) as noted in graphs, D1 = NSR530P2T5G, LEDs are Rohm
SML312WBCW1, temperature = 25°C, VIN = 3.7 V, unless otherwise noted.
1.00
1.00
Matching(1-2)
Matching(1-3)
Matching (2-3)
0.80
0.60
0.60
MATCHING (%)
MATCHING (%)
Matching(1-2)
Matching(1-3)
Matching (2-3)
0.80
0.40
0.20
0.00
0.40
0.20
0.00
-0.20
-0.20
-0.60
-0.40
2048
1920
1792
1664
1536
1408
1280
1152
1024
896
768
640
512
384
256
128
0
2048
1920
1792
1664
1536
1408
1280
1152
1024
896
768
640
512
384
256
128
0
-0.40
BRIGHTNESS CODE
BRIGHTNESS CODE
C001
Linear Mapping, 25C, 3.7V
Exponential Mapping, 25C, 3.7V
2.50
2.50
Accuracy I1
Accuracy I1
Accuracy I2
Accuracy I3
1.50
1.00
1.50
1.00
2048
1792
1536
1280
1024
768
BRIGHTNESS CODE
C001
Figure 56. LED Current Accuracy
C001
Figure 57. LED Current Accuracy
Exponential Mapping, 25C, 3.7V
Linear Mapping, 25C, 3.7V
0.70
VH1
0.60
512
256
BRIGHTNESS CODE
0
2048
1792
1536
1280
1024
768
0.00
512
0.00
256
0.50
0
0.50
0.70
Accuracy I2
2.00
Accuracy I3
ACCURACY (%)
ACCURACY (%)
2.00
VH1
0.60
VH2
VH2
VH3
VH3
0.50
HEADROOM VOLTAGE (V)
0.50
HEADROOM VOLTAGE (V)
C001
Figure 55. LED Matching (Linear Mapping)
Figure 54. LED Matching (Exponential Mapping)
0.40
0.30
0.20
0.10
0.00
0.40
0.30
0.20
0.10
0.00
2048
1792
1536
1280
1024
768
512
BRIGHTNESS CODE
C001
Figure 58. LED Headroom Voltage (Mis-Matched Strings)
256
0
2048
1792
1536
1280
1024
768
512
256
0
BRIGHTNESS CODE
C001
Figure 59. LED Headroom Voltage (Mis-Matched Strings)
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
35
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
L1 = 10 µH (VLF403212-100M) or 22 µH (VLF504015-220M) as noted in graphs, D1 = NSR530P2T5G, LEDs are Rohm
SML312WBCW1, temperature = 25°C, VIN = 3.7 V, unless otherwise noted.
2.0
24Mhz
4Mhz
0.8Mhz
QUIESCENT CURRENT (mA)
1.8
1.6
1.4
1.2
1.0
0.8
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
2.50
VIN (V)
C001
Figure 60. Current vs PWM Sample Frequency
36
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
9 Power Supply Recommendations
9.1 Input Supply Bypassing
The LM36923 is designed to operate from an input supply range of 2.5 V to 5.5 V. This input supply should be
well regulated and be able to provide the peak current required by the LED configuration and inductor selected
without voltage drop under load transients (start-up or rapid brightness change). The resistance of the input
supply rail should be low enough such that the input current transient does not cause the LM36923 supply
voltage to droop more than 5%. Additional bulk decoupling located close to the input capacitor (CIN) may be
required to minimize the impact of the input supply rail resistance.
10 Layout
10.1 Layout Guidelines
The LM36923's inductive boost converter sees a high switched voltage (up to VOVP) at the SW pin, and a step
current (up to ICL) through the Schottky diode and output capacitor each switching cycle. The high switching
voltage can create interference into nearby nodes due to electric field coupling (I = CdV/dt). The large step
current through the diode and the output capacitor can cause a large voltage spike at the SW pin and the OUT
pin due to parasitic inductance in the step current conducting path (V = Ldi/dt). Board layout guidelines are
geared towards minimizing this electric field coupling and conducted noise. Figure 61 highlights these two noisegenerating components.
Voltage Spike
VOUT + VF Schottky
Pulsed voltage at SW
IPEAK
Current through
Schottky and
COUT
IAVE = IIN
Current through
Inductor
Parasitic
Circuit Board
Inductances
Affected Node
due to Capacitive Coupling
LCD Display
Cp1
L
Lp1
D1
Lp2
Up to 29V
2.5 V to 5.5 V
COUT
IN
SW
Lp3
CIN
LM36923
OUT
LED1
LED2
LED3
GND
Figure 61. SW Pin Voltage (High Dv/Dt) and Current Through Schottky Diode and COUT (High Di/Dt)
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
37
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
Layout Guidelines (continued)
The following list details the main (layout sensitive) areas of the LM36923's inductive boost converter in order of
decreasing importance:
• Output Capacitor
– Schottky Cathode to COUT+
– COUT– to GND
• Schottky Diode
– SW pin to Schottky Anode
– Schottky Cathode to COUT+
• Inductor
– SW Node PCB capacitance to other traces
• Input Capacitor
– CIN+ to IN pin
10.1.1 Boost Output Capacitor Placement
Because the output capacitor is in the path of the inductor current discharge path it detects a high-current step
from 0 to IPEAK each time the switch turns off and the Schottky diode turns on. Any inductance along this series
path from the cathode of the diode through COUT and back into the LM36923's GND pin contributes to voltage
spikes (VSPIKE = LP_ × di/dt) at SW and OUT. These spikes can potentially overvoltage the SW pin, or feed
through to GND. To avoid this, COUT+ must be connected as close as possible to the cathode of the Schottky
diode, and COUT− must be connected as close as possible to the LM36923's GND pin. The best placement for
COUT is on the same layer as the LM36923 in order to avoid any vias that can add excessive series inductance.
10.1.2 Schottky Diode Placement
In the LM36923's boost circuit the Schottky diode is in the path of the inductor current discharge. As a result the
Schottky diode sees a high-current step from 0 to IPEAK each time the switch turns off and the diode turns on.
Any inductance in series with the diode causes a voltage spike (VSPIKE = LP_ × di/dt) at SW and OUT. This can
potentially over-voltage the SW pin, or feed through to VOUT and through the output capacitor and into GND.
Connecting the anode of the diode as close as possible to the SW pin and the cathode of the diode as close as
possible to COUT and reduces the inductance (LP_) and minimize these voltage spikes.
10.1.3 Inductor Placement
The node where the inductor connects to the LM36923's SW pin has 2 issues. First, a large switched voltage (0
to VOUT + VF_SCHOTTKY) appears on this node every switching cycle. This switched voltage can be capacitively
coupled into nearby nodes. Second, there is a relatively large current (input current) on the traces connecting the
input supply to the inductor and connecting the inductor to the SW bump. Any resistance in this path can cause
voltage drops that can negatively affect efficiency and reduce the input operating voltage range.
To reduce the capacitive coupling of the signal on SW into nearby traces, the SW bump-to-inductor connection
must be minimized in area. This limits the PCB capacitance from SW to other traces. Additionally, high
impedance nodes that are more susceptible to electric field coupling need to be routed away from SW and not
directly adjacent or beneath. This is especially true for traces such as SCL, SDA, HWEN, BL_ADJ, and PWM. A
GND plane placed directly below SW dramatically reduces the capacitance from SW into nearby traces.
Lastly, limit the trace resistance of the VIN to inductor connection and from the inductor to SW connection, by use
of short, wide traces.
10.1.4 Boost Input Capacitor Placement
For the LM36923 boost converter, the input capacitor filters the inductor current ripple and the internal MOSFET
driver currents during turn on of the internal power switch. The driver current requirement can range from 50 mA
at 2.7 V to over 200 mA at 5.5 V with fast durations of approximately 10 ns to 20 ns. This appears as high di/dt
current pulses coming from the input capacitor each time the switch turns on. Close placement of the input
capacitor to the IN pin and to the GND pin is critical since any series inductance between IN and CIN+ or CIN−
and GND can create voltage spikes that could appear on the VIN supply line and in the GND plane. Close
38
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
Layout Guidelines (continued)
placement of the input bypass capacitor at the input side of the inductor is also critical. The source impedance
(inductance and resistance) from the input supply, along with the input capacitor of the LM36923, form a series
RLC circuit. If the output resistance from the source (RS) is low enough the circuit is underdamped and has a
resonant frequency (typically the case). Depending on the size of LS the resonant frequency could occur below,
close to, or above the LM36923 switching frequency. This can cause the supply current ripple to be:
1. Approximately equal to the inductor current ripple when the resonant frequency occurs well above the
LM36923 switching frequency;
2. Greater than the inductor current ripple when the resonant frequency occurs near the switching frequency; or
3. Less than the inductor current ripple when the resonant frequency occurs well below the switching frequency.
Figure 62 shows the series RLC circuit formed from the output impedance of the supply and the input capacitor.
The circuit is redrawn for the AC case where the VIN supply is replaced with a short to GND, and the LM36923 +
Inductor is replaced with a current source (ΔIL). Equation 1 is the criteria for an underdamped response. Equation
2 is the resonant frequency. Equation 3 is the approximated supply current ripple as a function of LS, RS, and
CIN. As an example, consider a 3.6-V supply with 0.1 Ω of series resistance connected to CIN through 50 nH of
connecting traces. This results in an underdamped input-filter circuit with a resonant frequency of 712 kHz. Since
both the 1-MHz and 500-kHz switching frequency options lie close to the resonant frequency of the input filter,
the supply current ripple is probably larger than the inductor current ripple. In this case, using equation 3, the
supply current ripple can be approximated as 1.68 times the inductor current ripple (using a 500-kHz switching
frequency) and 0.86 times the inductor current ripple using a 1-MHz switching frequency. Increasing the series
inductance (LS) to 500 nH causes the resonant frequency to move to around 225 kHz, and the supply current
ripple to be approximately 0.25 times the inductor current ripple (500-kHz switching frequency) and 0.053 times
for a 1-MHz switching frequency.
'IL
ISUPPLY
RS
LS
LM36923
L
SW
+
IN
VIN Supply
-
CIN
ISUPPLY
LS
RS
CIN
'IL
2
1.
RS
1
>
LS x CIN 4 x LS2
2. f RESONANT =
1
2S LS x CIN
3. I SUPPLYRIPP LE | 'IL x
1
2S x 500 kHz x CIN
2
·
§
1
2
¸
RS + ¨¨2S x 500 kHz x LS ¸
2
S
x
500
kHz
x
C
IN ¹
©
Figure 62. Input RLC Network
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
39
LM36923
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
www.ti.com
10.2 Layout Example
VIA
Input Cap
5.0 mm
Inner or
Bottom Layer
Diode
Top Layer
BLADJ
Inductor
Output Cap
OUT
6.5 mm
Figure 63. LM36923 Layout Example
40
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
LM36923
www.ti.com
SNVSA30A – MARCH 2015 – REVISED OCTOBER 2016
11 Device and Documentation Support
11.1 Device Support
11.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.2 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
11.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.4 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.5 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
11.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
Submit Documentation Feedback
Copyright © 2015–2016, Texas Instruments Incorporated
Product Folder Links: LM36923
41
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)
LM36923YFFR
ACTIVE
DSBGA
YFF
12
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
36923
(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