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LM3556
SNVS796D – AUGUST 2011 – REVISED OCTOBER 2015
LM3556 1.5-A Synchronous Boost LED Flash Driver With High-Side Current Source
1 Features
3 Description
•
The LM3556 is a 4-MHz fixed-frequency synchronous
boost converter plus 1.5-A constant current driver for
a high-current white LED. The high-side current
source allows for grounded cathode LED operation
providing flash current up to 1.5 A. An adaptive
regulation method ensures the current source
remains in regulation and maximizes efficiency.
1
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Grounded Cathode LED Operation for Improved
Thermal Management
1.5-A High-Side Current Source for Single LED
Accurate and Programmable LED Current from
46.9 mA to 1.5 A
> 85% Efficiency in Torch Mode (at 100 mA) and
Flash Mode (at 1 A to 1.5 A)
Small Solution Size: < 20 mm2
LED Thermal Sensing and Current Scale-Back
Soft-Start Operation for Battery Protection
Hardware Enable Pin
Hardware Torch Enable
Hardware Strobe Enable
Synchronization Input for RF Power Amplifier
Pulse Events
VIN Flash Monitor Optimization
400-kHz I2C-Compatible Interface
I2C-Compatible Programmable NTC Trip Point
0.4-mm Pitch, 16-Pin DSBGA Package
The LM3556 is controlled via an I2C-compatible
interface. Features include: a hardware flash enable
(STROBE) allowing a logic input to trigger the flash
pulse, a hardware torch enable (TORCH) for Movie
Mode or flashlight functions, a TX input which forces
the flash pulse into a low-current Torch Mode
allowing for synchronization to RF power amplifier
events or other high-current conditions, and an
integrated comparator designed to monitor an NTC
thermistor and provide an interrupt to the LED
current. With a fast 1-μs transition from 0 mA to
46.9 mA, the TORCH input pin can be used to
develop custom LED current waveforms.
The 4-MHz switching frequency, overvoltage
protection and adjustable current limit allow for the
use of tiny, low-profile inductors and 10-µF ceramic
capacitors. The device is operates over a −40°C to
+85°C temperature range.
2 Applications
Camera Phone LED Flash
Device Information(1)
PART NUMBER
PACKAGE
LM3556
DSBGA (16)
BODY SIZE (MAX)
1.69 mm × 1.64 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Application Circuit
1 PH
IN
2.5 V to 5.5 V
SW
OUT
10 PF
10 PF
LED
ENABLE
STROBE
TORCH
TX
SDA
SCL
GND
Flash
LED
TEMP
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.
LM3556
SNVS796D – AUGUST 2011 – REVISED OCTOBER 2015
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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 ..........................................
Timing Requirements ................................................
Typical Characteristics ..............................................
Detailed Description ............................................ 12
7.1
7.2
7.3
7.4
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
12
13
13
15
7.5 Programming........................................................... 17
7.6 Register Maps ......................................................... 19
8
Application and Implementation ........................ 27
8.1 Application Information............................................ 27
8.2 Typical Application ................................................. 27
9 Power Supply Recommendations...................... 29
10 Layout................................................................... 30
10.1 Layout Guidelines ................................................. 30
10.2 Layout Example .................................................... 31
11 Device And Documentation Support................. 32
11.1
11.2
11.3
11.4
11.5
11.6
Device Support ....................................................
Documentation Support ........................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
32
32
32
32
32
32
12 Mechanical, Packaging, And Orderable
Information ........................................................... 33
4 Revision History
Changes from Revision C (April 2013) to Revision D
•
2
Page
Added Device Information and Pin Configuration and Functions sections, ESD Rating table, Feature Description,
Device Functional Modes, Application and Implementation, Power Supply Recommendations, Layout, Device and
Documentation Support, and Mechanical, Packaging, and Orderable Information sections ................................................. 1
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SNVS796D – AUGUST 2011 – REVISED OCTOBER 2015
5 Pin Configuration And Functions
YFQ Package
16-Pin DSBGA
Top View
A1
A2
A3
A4
B1
B2
B3
B4
C1
C2
C3
C4
D1
D2
D3
D4
Pin Functions
PIN
NUMBER
NAME
TYPE
DESCRIPTION
A1, B1
LED
Power
High-side current source output for flash LED. Both pins must be connected for proper
operation.
B2, A2
OUT
Power
Step-up DC-DC converter output. Connect a 10-µF ceramic capacitor between this pin
and GND.
B3, A3
SW
Power
Drain connection for internal NMOS and synchronous PMOS switches.
A4, B4
GND
Ground
Ground
C1
TEMP
Power
Threshold detector for LED temperature sensing and current scale back.
C2
TORCH
Power
Active high hardware torch enable. Drive TORCH high to turn on Torch or Movie mode.
Used for external PWM Mode. Has an internal pulldown resistor of 300 kΩ between
TORCH and GND.
C3
STROBE
I/O
Active high hardware flash enable. Drive STROBE high to turn on flash pulse. STROBE
overrides TORCH. Has an internal pulldown resistor of 300 kΩ between STROBE and
GND.
C4
IN
Input
Input voltage connection. Connect IN to the input supply, and bypass to GND with a 10µF or larger ceramic capacitor.
D1
TX
I/O
Configurable dual polarity power amplifier synchronization input. Has an internal pulldown
resistor of 300 kΩ between TX and GND.
D2
SDA
I/O
Serial data input/output.
D3
SCL
Input
D4
ENABLE
Power
Serial clock input.
Active high enable pin. High = standby, low = shutdown/reset. There is no internal
pulldown resistor on this pin.
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SNVS796D – AUGUST 2011 – REVISED OCTOBER 2015
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
(2)
VIN, VSW ,VOUT
MIN
MAX
UNIT
–0.3
6
V
−0.3 V to the lesser of (VIN + 0.3 V)
w/ 6 V maximum
VSCL, VSDA, VENABLE, VSTROBE, VTX, VTORCH, VLED, VTEMP
Continuous power dissipation (3)
Internally limited
Junction temperature, TJ-MAX
150
Storage temperature, Tstg
(1)
(2)
(3)
(4)
°C
See (4)
Maximum lead temperature (soldering)
°C
–65
150
°C
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltages are with respect to the potential at the GND pin.
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typical) and
disengages at TJ = 135°C (typical). Thermal shutdown is ensured by design.
For detailed soldering specifications and information, refer to Texas Instruments Application Note 1112: DSBGA Wafer Level chip Scale
Package (SNVA009).
6.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±1000
Charged-device model (CDM), per JEDEC specification JESD22-C101 (2)
±250
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted) (1) (2)
MIN
VIN
NOM
MAX
UNIT
2.5
5.5
V
Junction temperature, TJ
−40
125
°C
Ambient temperature, TA (2)
−40
85
°C
(1)
(2)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
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 (RθJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX).
6.4 Thermal Information
LM3556
THERMAL METRIC
(1)
YFQ (DSBGA)
UNIT
16 PINS
RθJA (2)
(1)
(2)
4
Junction-to-ambient thermal resistance
60
°C/W
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
Junction-to-ambient thermal resistance (RθJA) 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 102 mm × 76 mm × 1.6 mm with a 2 × 1
array of thermal vias. The ground plane on the board is 50 mm × 50 mm. Thickness of copper layers are 36 µm/18 µm/18 µm/36 µm
(1.5 oz/1 oz/1 oz/1.5 oz). Ambient temperature in simulation is 22°C, still air. Power dissipation is 1 W.
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6.5 Electrical Characteristics
Unless otherwise specified, VIN = 3.6 V, typical limits apply for TA = 25°C, and minimum (MIN) and maximum (MAX) limits
apply over the full operating ambient temperature range (−40°C ≤ TA ≤ +85°C). (1) (2)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
1.425
(–5%)
1.5
1.575
(+5%)
A
CURRENT SOURCE SPECIFICATIONS
ILED
Current source accuracy
1.5-A Flash, VOUT = 4 V
46.88-mA Torch, VOUT = 3.6 V
47
51.7 (+10%)
ILED = 1.5 A
Flash
250
280 (+12%)
ILED = 46.88 mA
Torch
150
172.5 (+15%)
VHR
Current source regulation
voltage
VOVP
Output overvoltage protection ON Threshold
trip point
OFF Threshold
42.3 (−10%)
4.86
5
5.1
4.75
4.88
4.99
mA
mV
V
STEP-UP DC-DC CONVERTER SPECIFICATIONS
RPMOS
PMOS switch on-resistance
IPMOS = 1 A
85
RNMOS
NMOS switch on-resistance
INMOS = 1 A
65
ICL
Switch current limit
mΩ
−12%
1.7
12%
−12%
1.9
12%
−10%
2.5
10%
−12%
3.1
12%
A
VTRIP
NTC comparator trip
threshold
Configuration Register, bit [1] = 1
−6%
600
6%
mV
UVLO
Undervoltage lockout
threshold
Falling VIN
2.74
2.8
2.85
V
INTC
NTC current
−6%
75
6%
µA
VIVFM
Input voltage flash monitor
trip threshold
–3.2%
2.9
3.2%
V
ƒSW
Switching frequency
2.5 V ≤ VIN ≤ 5.5 V
4
4.28
MHz
IQ
Quiescent supply current
Device not switching Pass Mode
0.6
0.75
mA
ISD
Shutdown supply current
Device disabled, EN = 0V
2.5 V ≤ VIN ≤ 5.5 V
0.1
1.3
µA
ISB
Standby supply current
Device disabled, EN = 2 V
2.5 V ≤ VIN ≤ 5.5 V
2.5
4
µA
tTX
Flash-to-torch LED current
settling time
TX low to high,
ILED = 1.5 A to 46.88 mA
IOS
ILED overshoot in external
indicator mode
0 mA to ITORCH
3.72
4
µs
8%
ENABLE, STROBE, TORCH, TX VOLTAGE SPECIFICATIONS
VIL
Input logic low
VIH
Input logic high
2.5 V ≤ VIN ≤ 5.5 V
0
0.4
1.2
VIN
V
I2C-COMPATIBLE INTERFACE SPECIFICATIONS (SCL, SDA)
VIL
Input logic low
VIH
Input logic high
VOL
Output logic low
(1)
(2)
2.5 V ≤ VIN ≤ 4.2 V
ILOAD = 3 mA
0
0.4
1.2
VIN
400
V
mV
Minimum and maximum limits are specified by design, test, or statistical analysis. Typical numbers are not verified, but do represent the
most likely norm. Unless otherwise specified, conditions for typical specifications are: VIN = 3.6 V and TA = 25°C.
All voltages are with respect to the potential at the GND pin.
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6.6 Timing Requirements
MIN
NOM
MAX
UNIT
t1
SCL clock frequency
2.4
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
Figure 1. I2C-Compatible Timing Diagram
6
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6.7 Typical Characteristics
1.60
100
TA = -40°C
TA = +25°C
TA = +85°C
90
EFFLED(%)
ILED(A)
1.55
1.50
1.45
80
70
TA = -40°C
TA = +25°C
TA = -+85°C
60
50
1.40
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
VIN(V)
VLED = 3.6 V
2.7
ILED = 1.5 A
3.5
VLED = 3.6 V
Figure 2. Flash LED Current vs VIN
3.9 4.3
VIN(V)
4.7
5.1
5.5
ILED = 1.5 A
Figure 3. Flash LED Efficiency vs VIN
100
0.400
96
0.393
92
0.385
88
0.378
84
ILED(A)
EFFLED(%)
3.1
80
0.370
VIN =4.2V
VIN =3.9V
VIN =3.6V
VIN =3.3V
VIN =3.0V
VIN =2.7V
76
72
68
0.363
TA=25°C
TA=85°C
TA=-40°C
0.355
64
0.348
60
0.340
2.7 3.1 3.4 3.8 4.1 4.5 4.8 5.2 5.5
VIN (V)
0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5
ILED(A)
VLED = 3 V
VLED = 3.8 V
ILED = 375 mA
Figure 5. Torch LED Current vs VIN
Figure 4. Flash LED Efficiency vs Flash LED Current
3.0
100
2.5
90
IQ STANDBY ( A)
LED EFFICIENCY (%)
95
85
80
75
70
65
60
55
TA=25°C
TA=85°C
TA=-40°C
2.0
1.5
1.0
0.5
25°C
85°C
- 40°C
0.0
50
2.7
2.7 3.1 3.4 3.8 4.1 4.5 4.8 5.2 5.5
VIN (V)
VLED = 3 V
3.1
3.5
3.9 4.3
VIN (V)
4.7
5.1
5.5
EN = 1.8 V
Figure 6. Torch LED Efficiency vs VIN
Figure 7. IQ Standby vs VIN
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Typical Characteristics (continued)
1.000
5.24
5.22
5.20
0.1
OVP (V)
Iq SHUTDOWN ( A)
85°C
0.01
5.16
5.14
25°C
25°C
85°C
- 40°C
5.12
-40°C
0.001
2.7
5.18
5.10
3.1
3.5
3.9
4.3
4.7
5.1
2.7
3.1
VIN (V)
3.5
3.9 4.3
VIN (V)
4.7
5.1
5.5
EN = 0 V
Figure 9. Variation of OVP With VIN
Figure 8. IQ Shutdown vs VIN
1.92
4.133
PEAK INPUT CURRENT (A)
SWITCHING FREQUENCY (MHz)
4.150
4.116
4.099
4.082
4.066
4.048
4.031
4.015
25°C
85°C
- 40°C
3.997
3.980
2.7
3.0
3.3
3.6
3.9
VIN (V)
4.2
1.88
1.84
25°C
- 40°C
85°C
1.80
1.76
1.72
1.68
1.64
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2
VIN (V)
4.5
Current Limit = 1.7 A
Figure 10. Frequency With VIN and Over Temperature
Figure 11. Input Current Limit Over Temperature and VIN
2.25
2.20
3.1
25°C
- 40°C
85°C
PEAK INPUT CURRENT (A)
PEAK INPUT CURRENT (A)
2.30
2.15
2.10
2.05
2.00
1.95
2.9
2.8
25°C
- 40°C
85°C
2.7
2.6
2.5
2.4
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4
VIN (V)
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2
VIN (V)
Current Limit = 1.9 A
Current Limit = 2.5 A
Figure 12. Input Current Limit Over Temperature and VIN
8
3.0
Figure 13. Input Current Limit Over Temperature and VIN
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Typical Characteristics (continued)
PEAK INPUT CURRENT (A)
3.52
3.50
3.48
3.46
1V/DIV
25°C
- 40°C
85°C
VIN
2V/DIV
3.44
3.42
1A/DIV
3.40
VOUT
3.38
1A/DIV
IIN
3.36
ILED
3.34
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2
VIN (V)
1 ms/DIV
Current Limit = 1.7 A
Current Limit = 3.1 A
Figure 14. Input Current Limit Over Temperature and VIN
Figure 15. Start-Up Plot With Part In Boost Mode Current
Limit
2V/DIV
STROBE
STROBE
2V/DIV
VOUT
2V/DIV
ILED
500mA/
DIV
IIN
1A/DIV
ILED
500 mA/
DIV
VOUT
2V/DIV
IIN
1A/DIV
100 ms/DIV
100ms/DIV
400 ms
400 ms
Figure 17. Strobe With Level-Triggered Signal
Figure 16. Strobe With Edge-Triggered Signal
100 mV/
DIV
VOUT
IIN
200 mA/
DIV
ILED
200 mA/
DIV
VIN
200 mV/
DIV
1A/DIV
1A/DIV
ILED
IIN
40 ms/DIV
400 s/DIV
Figure 18. Internal Indicator Operation
Figure 19. Input Voltage Flash Monitor Report Mode With
Default Settings
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Typical Characteristics (continued)
200 mV/
DIV
VIN
VIN
200 mV/
DIV
1A/DIV
1A/DIV
1A/DIV
ILED
ILED
1A/DIV
IIN
IIN
400 s/DIV
400 s/DIV
Figure 20. Input Voltage Flash Monitor Stop and Hold Mode
With Default Settings
VIN
200 mV/
DIV
Figure 21. Input Voltage Flash Monitor Down Mode With
Default Settings
VIN
200 mV/
DIV
1A/DIV
1A/DIV
ILED
ILED
1A/DIV
1A/DIV
IIN
IIN
400 s/DIV
400 s/DIV
0-mV Hysteresis
Figure 22. Input Voltage Flash Monitor Up and Down Mode
With Default Settings
1/2 Step Filter Time
Figure 23. Input Voltage Flash Monitor, Up and Down Mode
VIN
VIN
200 mV/
DIV
1A/DIV
200 mV/
DIV
1A/DIV
1A/DIV
ILED
ILED
1A/DIV
IIN
IIN
400 s/DIV
400 s/DIV
0-mV Hysteresis
256-µs Flash Ramp
512-ms Filter Time
Figure 24. Input Voltage Flash Monitor, Up and Down Mode
10
1/2 Step Filter Time
Figure 25. Input Voltage Flash Monitor, Up and Down Mode
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Typical Characteristics (continued)
2V/DIV
VOUT
2V/DIV
TX
2V/DIV
TX
VOUT
2V/DIV
500 mA/
DIV
500 mA/
DIV
ILED
ILED
1 s/DIV
400 s/DIV
Figure 27. Time Taken for LM3556 to Ramp from Torch to
Flash After TX Event
Figure 26. Impact on LED Current With a TX Event
VIN
200 mV/
DIV
ILED
200 mA/
DIV
40 s/DIV
Figure 28. Transient Plot When VIN Stepped from 3 → 2.9 V
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7 Detailed Description
7.1 Overview
The LM3556 is a high-power white LED flash driver capable of delivering up to 1.5 A into a single high-powered
LED. The device incorporates a 4-MHz constant-frequency synchronous current-mode PWM boost converter,
and a single high-side current source to regulate the LED current over the 2.5-V to 5.5-V input voltage range.
The LM3556 PWM converter switches and maintains at least VHR across the current source (LED). This
minimum headroom voltage ensures that the current source remains in regulation. If the input voltage is above
the LED voltage plus current source headroom voltage, the device does not switch, and turns the PFET on
continuously (Pass Mode). In Pass Mode the difference between (VIN − ILED × RPMOS) and the voltage across the
LED is dropped across the current source.
The LM3556 has three logic inputs including a hardware flash enable (STROBE), a hardware torch enable
(TORCH) used for external torch mode control and custom LED indication waveforms, and a flash interrupt input
(TX) designed to interrupt the flash pulse during high battery-current conditions. All three logic inputs have
internal 300-kΩ (typical) pulldown resistors to GND.
Additional features of the LM3556 include an internal comparator for LED thermal sensing via an external NTC
thermistor and an input voltage monitor that can reduce the Flash current (during low VIN conditions).
Control of the LM3556 is done via an I2C-compatible interface. This includes adjustment of the flash and torch
current levels, changing the flash time-out duration, changing the switch current limit, and enabling the NTC
block. Additionally, there are flag and status bits that indicate flash current time-out, LED overtemperature
condition, LED failure (open or short), device thermal shutdown, TX interrupt, and VIN undervoltage conditions.
12
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7.2 Functional Block Diagram
SW
Over Voltage
Comparator
IN
4 MHz
Oscillator
+
-
VREF
85 m:
Input Voltage
Flash Monitor
UVLO
VOVP
OUT
ILED
+
-
+
-
PWM
Control
65 m:
INTC
Thermal
Shutdown
+150°C
TEMP
+
-
LED
Error
Amplifier
+
-
+
-
OUT-VHR
Current Sense/
Current Limit
NTC VTRIP
Slope
Compensation
SDA
Control
Logic/
Registers
2
SCL
I C
Interface
ENABLE
Soft-Start
TORCH
STROBE
TX
GND
7.3 Feature Description
7.3.1 Power-Amplifier Synchronization (TX)
The TX pin is a power-amplifier synchronization input. It is designed to reduce the flash LED current and thus
limit the battery current during high battery-current conditions such as PA transmit events. When the LM3556 is
engaged in a flash event, and the TX pin is pulled high, the LED current is forced into Torch Mode at the
programmed torch current setting or shutdown. If the TX pin is then pulled low before the flash pulse terminates,
the LED current returns to the previous flash current level. At the end of the flash time-out, whether the TX pin is
high or low, the LED current turns off. The polarity of the TX input can be changed from active high to active low
through the Configuration Register (0x07) and can be disabled/enabled by setting the TX Enable bit in the
Enable Register (0x0A) to a '0'.
7.3.2 Input Voltage Flash Monitor (IVFM)
The LM3556 device can adjust the flash current based upon the voltage level present at the IN pin using an input
voltage flash monitor. Two adjustable thresholds (IVM-D and IVM-U) ranging from 2.9 V to 3.6 V in 100-mV
steps, and four different usage modes (Report Mode, Stop and Hold Mode, Adjust Down Only Mode, Adjust Up
and Down Mode), are provided. The Flags Register has the fault flag set when the input voltage crosses the
IVM-D value. In Report Mode, apart from the fault flag triggering, no action is taken on the LED current.
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Feature Description (continued)
Additionally, the IVM-D threshold sets the input voltage boundary that forces the LM3556 to either stop ramping
the flash current during start-up (Stop and Hold Mode) or to start decreasing the LED current during the flash
(Adjust Down Only Mode and Adjust Down and Up Mode). The IVM-U threshold sets the input voltage boundary
that forces the LM3556 to start ramping the flash current back up towards the target (Adjust Up and Down
Mode). The IVM-U threshold is equal to the IVM-D value plus the programmed hysteresis value also stored in the
Input Voltage Flash Monitor (IVFM) Mode Register (0x01).
To help prevent a premature current reduction, the LM3556 has four different filter timers that start once the input
voltage decreases below the IVM-D line. These filter times are set in the Silicon Revision and Filter Time
Register (0x00). For more information, refer to Input Voltage Flash Monitor (IVFM) Mode Register (0x01) and
Configuration Register (0x07).
7.3.3 Fault Protections
7.3.3.1 Fault Operation
Upon entering a fault condition, the LM3556 sets the appropriate flag in the Flags Register (0x0B), placing the
part into standby by clearing and locking the Torch Enable bit (TEN), Pre-Charge bit, and Mode bits (M1, M0) in
the Enable Register (0x0A), until the Flags Register (0x0B) is read back via I2C.
7.3.3.2 Flash Time-Out
The Flash time-out period sets the amount of time that the flash current is being sourced from the current source
(LED). The LM3556 has 8 time-out levels ranging 100 ms to 800 ms in 100-ms steps. The flash time-out period
is controlled in the Flash Features Register (0x08). Flash time-out only applies to the Flash Mode operation. The
mode bits are cleared upon a flash time-out.
7.3.3.3 Overvoltage Protection (OVP)
The output voltage is limited to typically 5 V (see VOVP in Electrical Characteristics . In situations such as an open
LED, the LM3556 device raises the output voltage in order to keep the LED current at its target value. When
VOUT reaches 5 V (typical), the overvoltage comparator trips and turns off the internal NFET. When VOUT falls
below the VOVP off threshold, the LM3556 begins switching again. The mode bits in the Enable Register (0x0A)
are not cleared upon an OVP.
7.3.3.4 Current Limit
The LM3556 features selectable inductor-current limits that are programmable through the Flash Features
Register (0x08) of the I2C-compatible interface. When the inductor-current limit is reached, the LM3556
terminates the charging phase of the switching cycle.
Because 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 Boost Mode or Pass Mode, if VOUT falls below 2.3 V, the device stops
switching, and the PFET operates as a current source limiting the current to 200 mA. This prevents damage to
the LM3556 and excessive current draw from the battery during output short-circuit conditions. The mode bits in
the Enable Register (0x0A) are not cleared upon a current limit event.
Pulling additional current from the VOUT node during normal operation is not recommended.
7.3.3.5 NTC Thermistor Input (TEMP)
The TEMP pin serves as a threshold detector for negative temperature coefficient (NTC) thermistors. It interrupts
the LED current when the voltage at TEMP goes below the programmed threshold. The NTC threshold voltage is
adjustable from 200 mV to 900 mV in 100-mV steps. The NTC current is adjustable from 25 µA to 100 µA in 25µA steps. When an overtemperature event is detected, the LM3556 can be set to force the LED current from
Flash Mode into Torch Mode or into shutdown. These settings are adjusted via the NTC Settings Register (0x02),
and the NTC detection circuitry can be enabled or disabled via the Enable Register (0x0A). If enabled, the NTC
block turns on and off during the start and stop of a flash, torch, or indicator event. The NTC mode of operation is
set by adjusting the NTC Mode bit in the Configuration Register (0x07). See NTC Settings Register (0x02) for
more details. The mode bits in the Enable Register (0x0A) are cleared upon an NTC event.
14
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Feature Description (continued)
7.3.3.6 Undervoltage Lockout (UVLO)
The LM3556 has an internal comparator that monitors the voltage at IN and forces the LM3556 into shutdown if
the input voltage drops to 2.8 V. If the UVLO monitor threshold is tripped, the UVLO flag bit is set in the Flags
Register (0x0B). If the input voltage rises above 2.8 V, the device is available for operation until there is an I2C
read command initiated for the Flags Register (0x0B). Upon a read, the Flags Register is cleared, and normal
operation can resume. This feature can be disabled by writing a '0' to the UVLO EN bit in the Input Voltage Flash
Monitor (IVFM) Mode Register (0x01). The mode bits in the Enable Register (0x0A) are cleared upon a UVLO
event.
7.3.3.7 Thermal Shutdown (TSD)
When the LM3556 device’s die temperature reaches 150°C, the boost converter shuts down, and the NFET and
PFET turn off, as does the current source (LED). When the thermal shutdown threshold is tripped, a '1' gets
written to the corresponding bit of the Flags Register (0x0B) (TSD bit), and the device goes into standby. The
LM3556 can only restart after the Flags Register (0x0B) is read, clearing the fault flag. Upon restart, if the die
temperature is still above 150°C, the device resets the fault flag and re-enters standby. The mode bits in the
Enable Register (0x0A) are cleared upon a TSD.
7.3.3.8 LED and/or VOUT Fault
The LED fault flag in the Flags Register (0x0B) reads back a '1' if the part is active in Flash Mode or Torch Mode,
and the LED output or the VOUT node experiences a short condition. The LM3556 determines an LED open
condition if the OVP threshold is crossed at the OUT pin while the device is in Flash or Torch Mode. An LED
short condition is determined if the voltage at LED goes below 500 mV (typical) while the device is in either
Torch or Flash Mode. There is a delay of 256-μs deglitch time before the LED flag is valid, and 2.048 ms before
the VOUT flag is valid. This delay is the time between when the flash or torch current is triggered and when the
LED voltage and the output voltage are sampled. The LED flag can only be reset to '0' by removing power to the
LM3556, or by reading back the Flags Register (0x0B). The mode bits in the Enable Register (0x0A) are cleared
upon an LED and/or VOUT fault.
7.4 Device Functional Modes
7.4.1 Start-Up (Enabling The Device)
Turnon of the LM3556 Torch and Flash Modes can be done through the Enable Register (0x0A). On start-up,
when VOUT is less than VIN the internal synchronous PFET turns on as a current source and delivers 200 mA
(typical) to the output capacitor. During this time the current source (LED) is off. When the voltage across the
output capacitor reaches 2.2 V (typical) the current source turns on. At turnon the current source steps through
each FLASH or TORCH level until the target LED current is reached. This gives the device a controlled turnon
and limits inrush current from the VIN supply.
7.4.2 Pass Mode
The LM3556 starts up in Pass Mode and stays there until Boost Mode is needed to maintain regulation. If the
voltage difference between VOUT and VLED falls below VHR, the device switches to Boost Mode. In Pass Mode the
boost converter does not switch, and the synchronous PFET fully turns on bringing VOUT up to (VIN − ILED ×
RPMOS). 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 A.
7.4.3 Flash Mode
In Flash Mode, the LED current source (LED) provides 16 target current levels from 93.75 mA to 1500 mA. The
Flash currents are adjusted via the Current Control Register (0x09). Flash mode is activated by the Enable
Register (0x0A), or by pulling the STROBE pin HIGH. Once the Flash sequence is activated the current source
(LED) ramps up to the programmed Flash current by stepping through all current steps until the programmed
current is reached.
When the device is enabled in Flash Mode through the Enable Register, all mode bits in the Enable Register are
cleared after a flash time-out event.
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Device Functional Modes (continued)
Data can be written to the mode bits (bits[1:0]) in Enable Register (0x0A) only after the flash has ramped down to
the desired value, and VOUT has decayed.
Table 1 shows the I2C commands and the state of the mode bits, if the STROBE pin is used to enable the Flash
Mode.
Table 1. I2C Commands and the State of the Mode Bits
MODE CHANGE REQUIRED
ENABLE AND CONFIGURATION
REGISTER SETTING (0x0A=Enable
Register, 0x07=Configuration Register)
STATUS OF MODE BITS IN THE ENABLE REGISTER AFTER
A FLASH
Using edge-triggered STROBE to Flash
0x0A = 0x23; 0x07 = 0x78 (default setting)
Mode bits are cleared after a single flash. To reflash, 0x23 has to
be written to 0x0A.
Using level-triggered STROBE to Flash
0x0A = 0x23; 0x07 = 0xF8
Mode bits are cleared after a single flash. To reflash, 0x23 has to
be written to 0x0A.
Part is required to go from external TORCH
Mode to external STROBE mode using
edge-triggered STROBE
0x0A = 0x33; 0x07 = 0x78 (default setting)
Mode bits are cleared after a single flash. To reflash, 0x33 has to
be written to 0x0A.
Part is required to go from external TORCH
Mode to external STROBE mode using
Level Triggered STROBE
0x0A = 0x33; 0x0 7= 0xF8
Mode bits are cleared only if the part has an internal flash timeout event happening before the STROBE level goes low. To reflash, 0x33 has to be written to 0x0A. If the STROBE level goes
low before an internal flash time-out event, then mode bits are not
cleared.
7.4.4 Torch Mode
In Torch Mode, the current source (LED) is programmed via the Current Control Register (0x09). Torch Mode is
activated by the Enable Register (0x0A) or by the hardware TORCH input. Once the Torch Mode is enabled the
current source ramps up to the programmed torch current level. The ramp-up and ramp-down times are
independently adjustable via the Torch Ramp Time Register (0x06). Torch Mode is not affected by flash timeout.
7.4.5 Indicator Mode
This mode has two options: the Internal Indicator Mode and the External Indicator mode. Both these modes are
activated by the Configuration Register (0x07) in addition to the Enable Register (0x0A).
In the Internal Indicator Mode, the current source (LED) can be programmed to 8 different intensity levels, with
current values being 1/8th the values in Current Control Register (0x09) bits [6:4]. The ramp-up, ramp-down, the
pulse time, number of blanks and periods of the desired output current can be independently controlled via the
Indicator Ramp Time Indicator (0x03), Indicator Blinking Register (0x04) and the Indicator Period Count Register
(0x05).
In the External Indicator Mode, the current source (LED) is controlled via the TORCH pin. An external PWM
signal can be input to the part via the TORCH pin to choose any one of the 8 available intensity settings (bits
[6:4] of the Current Control Register (0x09)) for the current source (LED).
16
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7.5 Programming
7.5.1 I2C-Compatible Interface
7.5.1.1 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 SCL is LOW.
SCL
SDA
data
change
allowed
data
valid
data
change
allowed
data
valid
data
change
allowed
Figure 29. Data Validity Diagram
A pullup resistor between the controller's VIO line and SDA must be greater than [(VIO – VOL) / 3mA] to meet the
VOL requirement on SDA. Using a larger pullup resistor results in lower switching current with slower edges, while
using a smaller pullup results in higher switching currents with faster edges.
7.5.1.2 Start and Stop Conditions
START and STOP conditions classify the beginning and the end of the I2C session. A START condition is
defined as the SDA signal transitioning from HIGH to LOW while SCL line is HIGH. A STOP condition is defined
as the SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master always generates START and
STOP conditions. The I2C bus is considered to be busy after a START condition and free after a STOP condition.
During data transmission, the I2C master can generate repeated START conditions. First START and repeated
START conditions are equivalent, function-wise.
SDA
SCL
S
P
Start Condition
Stop Condition
Figure 30. Start and Stop Conditions
7.5.1.3 Transferring Data
Every byte put on the SDA line must be eight bits long, with the most significant bit (MSB) 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 LM3556 pulls down
the SDA line during the 9th clock pulse, signifying an acknowledge. The LM3556 generates an acknowledge
after each byte is received. There is no acknowledge created after data is read from the LM3556.
After the START condition, the I2C master sends a chip address. This address is seven bits long followed by an
eighth bit which is a data direction bit (R/W). The LM3556 7-bit address is 0x63. 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.
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Programming (continued)
ack from slave
ack from slave
start
msb Chip Address lsb
w
ack
msb Register Add lsb
ack
start
Id = 63h
w
ack
addr = 0Ah
ack
ack from slave
msb
DATA
lsb
ack
stop
ack
stop
SCL
SDA
Data = 03h
W = Write (SDA = '0')
R = Read (SDA = '1')
Ack = Acknowledge (SDA Pulled Down By Either Master Or Slave)
ID= Chip Address, 63h For LM3556
Figure 31. Write Cycle
7.5.1.4 I2C-Compatible Chip Address
The device address for the LM3556 is 1100011 (63). After the START condition, the I2C-compatible master
sends the 7-bit address followed by an eighth read or write bit (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
1
Bit 6
0
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 32. I2C-Compatible Device Address
7.5.1.5 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 releases SDA (HIGH) during the 9th clock pulse. The LM3556 pulls down
SDA during the 9th clock pulse, signifying an acknowledge. An acknowledge is generated after each byte has
been received.
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7.6 Register Maps
7.6.1 Register Descriptions
INTERNAL HEX ADDRESS
POWER ON/RESET VALUE
Silicon Revision and Filter Time Register
REGISTER NAME
0x00
0x04
IVFM Mode Register
0x01
0x80
NTC Settings Register
0x02
0x12
Indicator Ramp Time Register
0x03
0x00
Indicator Blinking Register
0x04
0x00
Indicator Period Count Register
0x05
0x00
Torch Ramp Time Register
0x06
0x00
Configuration Register
0x07
0x78
Flash Features Register
0x08
0xD2
Current Control Register
0x09
0x0F
Enable Register
0x0A
0x00
Flags Register
0x0B
0x00
7.6.1.1 Silicon Revision and Filter Time Register (0x00)
Table 2. Silicon Revision and Filter Time Register Description
Bit 7
Bit 6
Bit 5
RFU
RFU
RFU
Bit 4
Bit 3
Bit 2
IVFM Filter Times
'00' = 1/2 of the Current Step Time
'01' = 256 µs
'10' =512 µs
'11' = 1024 µs
Bit 1
Bit 0
Bits available for Silicon Revision
Current Value = '100'
7.6.1.2 Input Voltage Flash Monitor (IVFM) Mode Register (0x01)
Table 3. Input Voltage Flash Monitor (IVFM) Mode Register Description
Bit 7
1 = UVLO EN
(default)
Bit 6
Bit 5
Hysteresis Level
00 = 50 mV (default)
01 = 100 mV
10 = 150 mV
11 = Hysteresis Disabled
Bit 4
Bit 3
IVM-D (Down) Threshold
000 = 2.9 V (default)
001 = 3 V
010 = 3.1 V
011 = 3.2 V
100 = 3.3 V
101 = 3.4 V
110 = 3.5 V
111 = 3.6 V
Bit 2
Bit 1
Bit 0
IVFM Adjust Mode
00 = Report Mode (default)
01 = Stop and Hold Mode
10 = Down Mode
11 = Up and Down Mode
00 = Report Mode Sets IVFM flag in Flags Register upon crossing IVM-D line Only. Does not adjust current.
01 = Stop and Hold Mode Stops current ramp and holds the level for the remaining flash if VIN crosses IVM-D
Line. Sets IVFM flag in Flags Register upon crossing IVM-D line.
10 = Down Mode Adjusts current down if VIN crosses IVM-D Line and stops decreasing once VIN rises above the
IVM-D line plus the IVFM hystersis setting. The LM3556 decreases the current throughout the flash
pulse anytime the input voltage falls below the IVM-D line, and not just once. The flash current does
not increase again until the next flash. Sets IVFM flag in Flags Register upon crossing IVM-D Line.
11 = Up and Down Mode Adjusts current down if VIN crosses IVM-D Line and adjusts current up if VIN rises
above the IVM-D line plus the IVFM hystersis setting. In this mode, the current continually adjusts
with the rising and falling of the input voltage throughout the entire flash pulse. Sets IVFM flag in
Flags Register upon crossing IVM-D Line.
UVLO EN
If enabled and VIN drops below 2.8 V, the LM3556 enters standby and sets the UVLO flag in the
Flags Register. Enabled = ‘1’, Disabled = ‘0’
IVM-U = IVM-D + IVFM Hysteresis
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IFLASH
ILED
0 mA
IVM-U
VIN
IVM-D
tfilter
tfilter
t
Figure 33. Stop and Hold Mode
IFLASH
ILED
0 mA
VIN IVM-U
IVM-D
t
tfilter
Figure 34. Adjust Down-Only Mode
IFLASH
ILED
0 mA
VIN IVM-U
IVM-D
t
tfilter
tfilter
tfilter
Figure 35. Adjust Up and Down Mode
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7.6.1.3 NTC Settings Register (0x02)
Table 4. NTC Settings Register Description
Bit 7
Bit 6
Bit 5
Bit 4
RFU
RFU
NTC Event
Level
0 = Go to
standby
(default)
1 = Reduce
to minimum
torch current
Bit 3
Bit 2
Bit 1
NTC Trip Thresholds
000 = 200 mV
001 = 300 mV
010 = 400 mV
011 = 50 mV
100 = 600 mV (default)
101 = 700 mV
110 = 800 mV
111 = 900 mV
Bit 0
NTC Bias Current Level
00 = 25 µA
01 = 50 µA
10 = 75 µA (default)
11 = 100 µA
VIN
NTC Control Block
INTC
TEMP
VTRIP
NTC
+
Control
Logic
Figure 36. NTC Control Block
The TEMP node is connected to an NTC resistor as shown in Figure 36 above. A constant current source from
the input is connected to this node. Any change in the voltage because of a change in the resistance of the NTC
resistor is compared to a set VTRIP. The trip thresholds are selected by Bits[4:2] of the NTC Register. The output
of the Control Logic upon an NTC trip is selected through Bit[5].
7.6.1.4 Indicator Ramp Time Indicator (0x03)
Table 5. Indicator Ramp Time Indicator Description
Bit 7
Bit 6
RFU
RFU
Bit 5
Bit 4
Bit 3
Indicator Ramp-Up Time (tR)
000 = 16 ms (default)
001 = 32 ms
010 = 64 ms
011 = 128 ms
100 = 256 ms
101 = 512 ms
110 = 1.024 s
111 = 2.048 s
Bit 2
Bit 1
Bit 0
Indicator Ramp-Down Time (tF)
000 = 16 ms (default)
001 = 32 ms
010 = 64 ms
011 = 128 ms
100 = 256 ms
101 = 512 ms
110 = 1.024 s
111 = 2.048 s
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7.6.1.5 Indicator Blinking Register (0x04)
Table 6. Indicator Blinking Register Description
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
NBLANK
0000 = 0 (default)
0001 = 1
0010 = 2
0011 = 3
0100 = 4
0101 = 5
0110 = 6
0111 = 7
1000 = 8
1001 = 9
1010 = 10
1011 = 11
1100 = 12
1101 = 13
1110 = 14
1111 = 15
Bit 2
Bit 1
Bit 0
Pulse Time (tPULSE)
0000 = 0 (default)
0001 = 32 ms
0010 = 64 ms
0011 = 92 ms
0100 = 128 ms
0101 = 160 ms
0110 = 196 ms
0111 = 224 ms
1000 = 256 ms
1001 = 288 ms
1010 = 320 ms
1011 = 352 ms
1100 = 384 ms
1101 = 416 ms
1110 = 448 ms
1111 = 480 ms
7.6.1.6 Indicator Period Count Register (0x05)
Table 7. Indicator Period Count Register Description
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
RFU
RFU
RFU
RFU
RFU
tPERIOD
Bit 2
Bit 1
Bit 0
NPERIOD
000 = 0 (default)
001 = 1
010 = 2
011 = 3
100 = 4
101 = 5
110 = 6
111 = 7
tBLANK
tPERIOD
tPULSE
tPULSE
ITORCH
tR
tF
tPULSE
tR
tF
tPULSE
Figure 37. Indicator Usage
1. Number of periods (tPERIOD = tR + tF + tPULSE × 2)
2. Active Time (tACTIVE = tPERIOD × NPERIOD)
3. Blank Time (tBLANK = tACTIVE × NBLANK)
tPERIOD
tBLANK
tPERIOD
Figure 38. Single Pulse With Dead Time
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tACTIVE
tPERIOD
tPERIOD
tBLANK
tPERIOD
Figure 39. Multiple Pulse With Dead Time
7.6.1.7 Torch Ramp Time Register (0x06)
Table 8. Torch Ramp Time Register
Bit 7
Bit 6
RFU
RFU
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Torch Ramp-Up Time
000 = 16 ms (default)
001 = 32 ms
010 = 64 ms
011 = 128 ms
100 = 256 ms
101 = 512 ms
110 = 1.024 s
111 = 2.048 s
Bit 0
Torch Ramp-Down Time
000 = 16 ms (default)
001 = 32 ms
010 = 64 ms
011 = 128 ms
100 = 256 ms
101 = 512 ms
110 = 1.024 s
111 = 2.048 s
7.6.1.8 Configuration Register (0x07)
Table 9. Configuration Register Description
Bit 7
Strobe Usage
0 = Edge
(default)
1 = Level
Bit 6
Bit 5
Bit 4
Bit 3
Strobe Pin
Torch Pin
TX Pin
TX Event Level
Polarity
Polarity
Polarity
0 = Off
0 = Active Low 0 = Active Low 0 = Active Low 1 = Torch Current
1 = Active
1 = Active
1 = Active
(default)
High (default)
High (default)
High (default)
Bit 2
Bit 1
Bit 0
IVFM Enable
0 = Disabled
(default)
1 = Enabled
NTC Mode
0 = Normal
(default)
1 = Monitor
Indicator Mode
0 = Internal
(default)
1 = External
Strobe Usage Level or edge. Flash follows strobe timing if Level and internal timing if edge.
Strobe Polarity Active high or active low select.
Torch Polarity Active high or active low select.
TX Polarity Active high or active low select.
TX Event Level Transition to torch current level or off setting if TX event occurs.
The TX Event Level off setting is designed to force a shutdown only during a flash event. When
Torch or Indicator Mode is enabled, and a TX event occurs with the TX event level set to Off , the
LM3556 does not shut down. The TX flag bit (bit7 in the Table 14) is set, and the mode bits (bit0
and bit1 in Table 12) get locked out until the fault register is cleared via an I2C read. Because a TX
event is periodic and frequently occurring, clearing the fault register becomes more difficult.
Depending on the I2C read/write speed and TX event frequency, it may be necessary to set the TX
enable bit (bit6 in the Table 12) to a '0' before clearing the fault register to prevent future flag sets.
IVFM Enable Enables input voltage flash monitoring.
NTC Mode
Monitor Mode (report only) or Normal Mode (reduce current or shutdown).
Indicator Mode Externally generated via TORCH pin or internally generated PWM.
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7.6.1.9 Flash Features Register (0x08)
Table 10. Flash Features Register Description
Bit 7
Bit 6
Bit 5
Bit 4
Inductor Current Limit
00 =1.7 A
01 = 1.9 A
10 = 2.5 A
11 = 3.1 A (default)
Bit 3
Bit 2
Flash Ramp Time
000 = 256 µs
001 = 512 µs
010 = 1.024 ms (default)
011 = 2.048 ms
100 = 4.096 ms
101 = 8.192 ms
110 = 16.384 ms
111 = 32.768 ms
Bit 1
Bit 0
Flash Time-Out Time
000 = 100 ms
001 = 200 ms
010 = 300 ms (default)
011 = 400 ms
100 = 500 ms
101 = 600 ms
110 = 700 ms
111 = 800 ms
7.6.1.10 Current Control Register (0x09)
Table 11. Current Control Register Description
Bit 7
Bit 6
RFU
Bit 5
Bit 4
Bit 3
Bit 2
Torch Current
000 = 46.88 mA (default)
001 =93.75 mA
010 =140.63 mA
011 = 187.5 mA
100 =234.38 mA
101 = 281.25 mA
110 = 328.13 mA
111 =375 mA
Bit 1
Bit 0
Flash Current
0000 = 93.75 mA
0001 = 187.5 mA
0010 = 281.25 mA
0011 = 375 mA
0100 = 468.75 mA
0101 = 562.5mA
0110 = 656.25 mA
0111 = 750 mA
1000 = 843.75 mA
1001 = 937.5 mA
1010 = 1031.25 mA
1011 = 1125 mA
1100 = 1218.75 mA
1101 = 1312.5 mA
1110 = 1406.25 mA
1111 = 1500 mA (default)
7.6.1.11 Enable Register (0x0A)
Table 12. Enable Register Description
Bit 7
NTC Enable
0 = Disabled
(default)
1 = Enabled
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
TX Pin Enable
0 = Disabled
(default)
1 = Enabled
STROBE Pin
Enable
0 = Disabled
(default)
1 = Enabled
TORCH Pin
Enable
0 = Disabled
(default)
1 = Enabled
PreCharge Mode
Enable
0 = Normal
(default)
1 = PreCharge
Pass-Mode
Only Enable
0 = Normal
(default)
1 = Pass Only
NTC EN
Enables NTC block.
TX EN
Allows TX events to change the current.
Strobe EN
Enables STROBE pin to start a flash event.
Torch EN
Enables TORCH pin to start a torch event.
Bit 1
Bit 0
Mode Bits: M1, M0
00 = Standby (default)
01 = Indicator
10 = Torch
11 = Flash
PreCharge Mode EN Enables Pass Mode to pre-charge the output cap.
Pass-Only Mode EN Only allows Pass Mode and disallows Boost Mode.
If Pass-Only Mode is enabled during any LED mode (Indicator, Torch or Flash), it remains enabled
until the LM3556 enters the standby state regardless of whether the Pass-Only Mode bit is reset or
not during the following command.
24
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7.6.1.11.1 Enable Register Mode Bits
00–Standby Off
01–Indicator Sets Indicator Mode. Default Indicator Mode uses external pattern on TORCH pin.
10–Torch
Sets Torch Mode with ramping. If Torch EN = 0, Torch starts after I2C-compatible command.
11–Flash
Sets Flash Mode with ramping. If Strobe EN = 0, Flash starts after I2C-compatible command.
7.6.1.11.2 Control Logic Delays
Strobe Controlled Flash Start and
Stop Delay Times
I2C Controlled Flash Start and Stop
Delay Times
I2C
Bus
I2C Flash
STROBE
I2C Stop
ILED
ILED
tb
ta
External Indicator Start and Stop
Delay Times
Using Torch Pin
TX event ± Start and Stop
Delay Times
TORCH
TX
ILED
EDGE TRIG
STROBE
te
td
tc
tf
ILED
tg
th
Flash time-out
Figure 40. Control Logic Delays
Table 13. Control Logic Delay Timing
DELAY
EXPLANATION
TIME
2
ta
Time for the LED current to start ramping up after an I C Write command.
tb
Time for the LED current to start ramping down after an I2C Stop command.
554 µs
32 µs
tc
Time for the LED current to start ramping up after the STROBE pin is raised high.
400 µs
td
Time for the LED current to start ramping down after the STROBE pin is pulled low.
16 µs
te
Time for the LED current to start ramping up after the TORCH pin is raised high.
300 µs
tf
Time for the LED current to start ramping down after the TORCH pin is pulled low.
16 µs
tg
Time for the LED current to start ramping down after the TX pin is pulled high.
3 µs
th
Time for the LED current to start ramping up after the TX pin is pulled low, provide the part has
not timed out in Flash Mode.
2 µs
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7.6.1.12 Flags Register (0x0B)
Table 14. Flags Register Description
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
TX Event
0 = Default
NTC Trip
0 = Default
IVFM
0 = Default
UVLO
0 = Default
OVP
0 = Default
LED or VOUT
Short Fault
0 = Default
Thermal
Shutdown
0 = Default
Flash Time-out
0 = Default
TX Event Flag TX event occurred.
NTC Trip Flag NTC threshold crossed.
IVFM Flag
IVFM block reported and/or adjusted LED current.
UVLO Fault UVLO threshold crossed.
OVP Flag
Overvoltage Protection tripped. Open output capacitor or open LED.
LED Short Fault LED short detected.
Thermal Shutdown Fault LM3556 die temperature reached thermal shutdown value.
Time-Out Flag Flash Timer tripped.
NOTE
Faults require a read-back of the Flags Register to resume operation. Flags report an
event occurred, but do not inhibit future functionality. A read-back of the Flags Register
updates again if the fault or flags are still present upon a restart.
26
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8 Application 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 LM3556 can drive one flash LED at currents up to 1.5 A. The 4-MHz DC-DC boost regulator allows for the
use of small-value discrete external components.
8.2 Typical Application
1 PH
IN
2.5 V to 5.5 V
SW
OUT
10 PF
10 PF
LED
ENABLE
STROBE
TORCH
TX
SDA
SCL
GND
Flash
LED
TEMP
Figure 41. LM3556 Typical Application
8.2.1 Design Requirements
Example requirements based on default register values are listed in Table 15:
Table 15. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input Voltage Range
2.5 V to 5.5 V
Brightness Control
I2C Register
Output current
1.5 A
LED Configuration
1 Flash LED
Switching frequency
4 MHz (typical)
8.2.2 Detailed Design Procedure
8.2.2.1 Output Capacitor Selection
The LM3556 is designed to operate with a ceramic output capacitor of at least 10 µF. When the boost converter
is running, the output capacitor supplies the load current during the boost converter's on-time. When the NMOS
switch turns off, the inductor energy is discharged through the internal PMOS switch, 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.
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Larger capacitors (for example, a 22-µF capacitor) or capacitors in parallel may 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 equivalent series resistance (ESR) (ΔVESR), use Equation 1 and Equation 2.
For continuous conduction mode, the output voltage ripple due to the capacitor discharge is:
ILED x (VOUT - VIN)
'VQ =
fSW x VOUT x COUT
(1)
The output voltage ripple due to the ESR of the output capacitor is found by:
'VESR = R ESR x §
©
where
'IL =
I LED x VOUT·
¹
VIN
+ 'I L
VIN x (VOUT - VIN )
2 x f SW x L x VOUT
(2)
In ceramic capacitors the ESR is very low so the assumption is that 80% of the output voltage ripple is due to
capacitor discharge and 20% from ESR. Table 16 lists different manufacturers for various output capacitors and
their case sizes suitable for use with the LM3556.
8.2.2.2 Input Capacitor Selection
Choosing the correct size and type of input capacitor helps minimize the voltage ripple caused by the switching
of the LM3556 device’s boost converter and reduces noise on the boost converter's input terminal that can feed
through and disrupt internal analog signals. In the Figure 41 a 10-µF ceramic input capacitor works well. It is
important to place the input capacitor as close as possible to the LM3556’s input (IN) pin. This reduces the series
resistance and inductance that can inject noise into the device due to the input switching currents. Table 16 lists
various input capacitors recommended for use with the LM3556.
Table 16. Recommended Input/Output Capacitors (X5R/X7R Dielectric)
MANUFACTURER
PART NUMBER
VALUE
CASE SIZE
VOLTAGE RATING
TDK Corporation
C1608JB0J106M
TDK Corporation
C2012JB1A106M
10 µF
0603 (1.6 mm × 0.8 mm × 0.8 mm)
6.3 V
10 µF
0805 (2 mm × 1.25 mm × 1.25 mm)
Murata
10 V
GRM188R60J106M
10 µF
0603 (1.6 mm x 0.8 mm x 0.8 mm)
6.3 V
Murata
GRM21BR61A106KE19
10 µF
0805 (2 mm × 1.25 mm × 1.25 mm)
10 V
8.2.2.3 Inductor Selection
The LM3556 is designed to use a 1-µH or 0.47-µH inductor. Table 17 lists various inductors and their
manufacturers that work well with the LM3556. When the device is boosting (VOUT > VIN) the inductor is typically
the largest 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 must be greater than the maximum
operating peak current of the LM3556. This prevents excess efficiency loss that can occur with inductors that
operate in saturation. For proper inductor operation and circuit performance, ensure that the inductor saturation
and the peak current limit setting of the LM3556 are greater than IPEAK in Equation 3:
I LOAD VOUT
VIN x (VOUT - VIN)
IPEAK =
K
x
VIN
+ 'IL where 'IL =
2 x f SW x L x VOUT
where
•
•
ƒSW = 4 MHz
Efficiency can be found in Typical Characteristics.
(3)
Table 17. Recommended Inductors
28
MANUFACTURER
L
PART NUMBER
DIMENSIONS (L × W × H)
ISAT
RDC
TOKO
1 µH
FDSD0312
3 mm x 3 mm x 1.2 mm
4.5 A
43 mΩ
TOKO
1 µH
DFE252010C
2.5 mm × 2 mm × 1 mm
3.4 A
60 mΩ
TOKO
1 µH
DFE252012C
2.5 mm × 2 mm × 1.2 mm
3.8 A
45 mΩ
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8.2.2.4 NTC Thermistor Selection
The TEMP pin is a comparator input for flash LED thermal sensing. NTC mode is intended to monitor an external
thermistor which monitors LED temperature and prevents LED overheating. An internal comparator checks the
voltage on the TEMP pin against the trip point programmed in the NTC Settings Register (0x02). The thermistor
is driven by an internally regulated current source, and the voltage on the TEMP pin is related to the source
current and the NTC resistance.
NTC thermistors have a temperature to resistance relationship of:
1
1
·
E§
T °C + 273 298
©
¹
R(T) = R25°C x e
where
•
•
β is given in the thermistor datasheet
R25°C is the thermistor's value at 25°C.
(4)
8.2.3 Application Curves
100
100
92
88
EFFLED(%)
EFFLED(%)
96
TA = -40°C
TA = +25°C
TA = +85°C
90
80
70
84
80
76
72
68
60
VIN =4.2V
VIN =3.9V
VIN =3.6V
VIN =3.3V
VIN =3.0V
VIN =2.7V
64
60
50
2.7
VLED = 3.6 V
3.1
3.5
3.9 4.3
VIN(V)
4.7
5.1
0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5
ILED(A)
5.5
ILED = 1.5 A
VLED = 3.8 V
Figure 42. Flash LED Efficiency vs VIN
Figure 43. Flash LED Efficiency vs Flash LED Current
9 Power Supply Recommendations
The LM3556 is designed to operate from an input supply range of 2.5 V to 5.5 V. This input supply must be well
regulated and provide the peak current required by the LED configuration and inductor selected.
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10 Layout
10.1 Layout Guidelines
The high switching frequency and large switching currents of the LM3556 make the choice of layout important.
The following steps should be used as a reference to ensure the device is stable and maintains proper LED
current regulation across its intended operating voltage and current range.
1. Place CIN on the top layer (same layer as the device), as close as possible to the device. The input capacitor
conducts the driver currents during the low-side MOSFET turnon and turnoff and can see current spikes over
1 A in amplitude. Connecting the input capacitor through short, wide traces to both the IN and GND pins
reduces the inductive voltage spikes that occur during switching which can corrupt the VIN line.
2. Place COUT on the top layer (same layer as the device) and as close as possible to the OUT and GND pins.
The returns for both CIN and COUT must come together at one point, as close as possible to the GND pin.
Connecting COUT through short, wide traces reduces the series inductance on the OUT and GND pins that
can corrupt the VOUT and GND lines and cause excessive noise in the device and surrounding circuitry.
3. Connect the inductor on the top layer close to the SW pin. There must be a low-impedance connection from
the inductor to SW due to the large DC inductor current, and at the same time the area occupied by the SW
node must be small to reduce the capacitive coupling of the high dV/dt present at SW that can couple into
nearby traces.
4. Logic traces must not be routed near the SW node to avoid any capacitively coupled voltages from SW onto
any high-impedance logic lines such as TORCH, STROBE, HWEN, TEMP, SDA, and SCL. A good approach
is to insert an inner layer GND plane underneath the SW node and between any nearby routed traces. This
creates a shield from the electric field generated at SW.
5. Terminate the flash LED cathodes directly to the GND pin of the LM3556. If possible, route the LED returns
with a dedicated path to keep the high amplitude LED currents out of the GND plane. For flash LEDs that are
routed relatively far away from the device, sandwich the forward and return current paths over the top of
each other on two layers. This helps reduce the inductance of the LED current paths.
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10.2 Layout Example
Figure 44. LM3556 Layout Example
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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 Documentation Support
11.2.1 Related Documentation
For additional information, see the following:
TI Application Note DSBGA Wafer Level Chip Scale Package (SNVA009)
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
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.
11.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
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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.
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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)
LM3556TME/NOPB
ACTIVE
DSBGA
YFQ
16
250
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
D36
LM3556TMX/NOPB
ACTIVE
DSBGA
YFQ
16
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
D36
(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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