TI1 LM3556 1.5a synchronous boost led flash driver w/ high-side current source Datasheet

LM3556
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SNVS796C – AUGUST 2011 – REVISED APRIL 2013
1.5A Synchronous Boost LED Flash Driver w/ High-Side Current Source
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FEATURES
DESCRIPTION
•
The LM3556 is a 4 MHz fixed-frequency synchronous
boost converter plus 1.5A 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 1.5A. An adaptive
regulation method ensures the current source
remains in regulation and maximizes efficiency.
1
2
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Grounded Cathode LED Operation for
Improved Thermal Management
1.5A High-Side Current Source for Single LED
Accurate and Programmable LED Current from
46.9 mA to 1.5A
> 85% Efficiency in Torch Mode (@ 100 mA)
and Flash Mode (@1A to 1.5A)
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-Bump 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, over-voltage
protection and adjustable current limit allow for the
use of tiny, low-profile inductors and (10 µF) ceramic
capacitors. The device is available in a small 16bump (1.660 mm x 1.610 mm x 0.6 mm) DSBGA
package and operates over the −40°C to +85°C
temperature range.
APPLICATIONS
•
Camera Phone LED Flash
TYPICAL APPLICATION CIRCUIT
1 PH
SW
IN
2.5V to 5.5V
OUT
10 PF
10 PF
LED
ENABLE
STROBE
TORCH
TX
SDA
SCL
Flash
LED
TEMP
GND
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2011–2013, Texas Instruments Incorporated
LM3556
SNVS796C – AUGUST 2011 – REVISED APRIL 2013
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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.
CONNECTION DIAGRAM
Top View
A1
A2
Top View
A3
A4
B1
B2
B3
B4
C1
C2
C3
C4
D1
D2
D3
D4
Pin 1A
Figure 1. 16-Bump DSBGA Package YFQ16ACA
PIN DESCRIPTIONS
Pin
2
Name
Description
A1, B1
LED
High-Side Current Source Output for Flash LED. Both bumps must be connected for proper
operation.
B2, A2
OUT
Step-Up DC/DC Converter Output. Connect a 10 µF ceramic capacitor between this pin and
GND.
B3, A3
SW
Drain Connection for Internal NMOS and Synchronous PMOS Switches.
A4, B4
GND
Ground
C1
TEMP
Threshold Detector for LED Temperature Sensing and Current Scale Back.
C2
TORCH
Active High Hardware Torch Enable. Drive TORCH high to turn on Torch/Movie Mode. Used
for External PWM mode. Has an internal pulldown resistor of 300 kΩ between TORCH and
GND.
C3
STROBE
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 Voltage Connection. Connect IN to the input supply, and bypass to GND with a 10 µF or
larger ceramic capacitor.
D1
TX
Configurable Dual Polarity Power Amplifier Synchronization Input. Has an internal pulldown
resistor of 300 kΩ between TX and GND.
D2
SDA
Serial Data Input/Output.
D3
SCL
Serial Clock Input.
D4
ENABLE
Active High Enable Pin. High = Standby, Low = Shutdown/Reset. There is no internal
pulldown resistor on this pin.
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TYPICAL LAYOUT
Table 1. Application Circuit Component List
Component
L
Manufacturer
TOKO
Value
1µH
Part-Number
FDSD0312-1R0
Size (mm)
Current/Voltage Rating
(Resistance)
3 mm x 3 mm x 1.2 mm
3.4A
6.3V
6.3V
COUT
Murata
10 µF
GRM188R60J106M
1.6 mm x 0.8 mm x 0.8 mm
(0603)
CIN
Murata
10 µF
GRM188R60J106M
1.6 mm x 0.8 mm x 0.8 mm
(0603)
LED
Lumiled
PWF-4
VF = 3.6V, @1.5A
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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
Figure 2. Block Diagram
4
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ABSOLUTE MAXIMUM RATINGS
(1) (2)
−0.3V to 6V
VIN, VSW ,VOUT
VSCL, VSDA, VENABLE, VSTROBE, VTX, VTORCH, VLED, VTEMP
−0.3V to the lesser of (VIN+0.3V) w/ 6V
max
Continuous Power Dissipation
(3)
Internally Limited
Junction Temperature (TJ-MAX)
+150°C
−65°C to +150°C
Storage Temperature Range
(4)
Maximum Lead Temperature (Soldering)
(1)
(2)
(3)
(4)
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.
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 (typ.) and
disengages at TJ=+135°C (typ.). Thermal shutdown is guaranteed by design.
For detailed soldering specifications and information, please refer to Texas Instruments Application Note 1112: DSBGA Wafer Level chip
Scale Package (AN-1112)
OPERATING RATINGS
(1) (2)
VIN
2.5V to 5.5V
−40°C to +125°C
Junction Temperature (TJ)
Ambient Temperature (TA)
(1)
(2)
(3)
(3)
−40°C to +85°C
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.
All voltages are with respect to the potential at the GND pin.
In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may
have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP =
+125°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to-ambient thermal resistance of the
part/package in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).
THERMAL PROPERTIES
Thermal Junction-to-Ambient Resistance (θJA)
(1)
(1)
60°C/W
Junction-to-ambient thermal resistance (θJA) is taken from a thermal modeling result, performed under the conditions and guidelines set
forth in the JEDEC standard JESD51-7. The test board is a 4-layer FR-4 board measuring 102 mm x 76 mm x 1.6 mm with a 2x1 array
of thermal vias. The ground plane on the board is 50 mm x 50 mm. Thickness of copper layers are 36 µm/18 µm/18 µm/36 µm (1.5
oz/1oz/1oz/1.5 oz). Ambient temperature in simulation is 22°C, still air. Power dissipation is 1W.
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ELECTRICAL CHARACTERISTICS
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(1) (2)
Limits in standard typeface are for TA = +25°C. Limits in boldface type apply over the full operating ambient temperature
range (−40°C ≤ TA ≤ +85°C). Unless otherwise specified, VIN = 3.6V.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
1.425
(-5%)
1.5
1.575
(+5%)
A
42.3
(−10%)
47
51.7
(+10%)
mA
Current Source Specifications
1.5A Flash, VOUT = 4V
ILED
Current Source Accuracy
46.88 mA Torch, VOUT = 3.6V
VHR
ILED = 1.5A
Flash
250
280
(+12%)
ILED = 46.88 mA
Torch
150
172.5
(+15%)
Current Source Regulation Voltage
VOVP
Output Over-Voltage Protection Trip ON Threshold
Point
OFF Threshold
4.86
5
5.1
4.75
4.88
4.99
mV
V
Step-Up DC/DC Converter Specifications
RPMOS
PMOS Switch On-Resistance
IPMOS = 1A
85
RNMOS
NMOS Switch On-Resistance
INMOS = 1A
65
mΩ
−12%
1.7
+12%
−12%
1.9
+12%
−10%
2.5
+10%
−12%
3.1
+12%
−6%
600
+6%
ICL
Switch Current Limit
VTRIP
NTC Comparator Trip Threshold
Configuration Register, bit [1] = 1
UVLO
Under Voltage 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
fSW
Switching Frequency
2.5V ≤ VIN ≤ 5.5V
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
2.5V ≤ VIN ≤ 5.5V
0.1
1.3
µA
ISB
Standby Supply Current
Device Disabled, EN = 2V
2.5V ≤ VIN ≤ 5.5V
2.5
4
µA
tTX
Flash-to-Torch LED Current Settling TX Low to High,
Time
ILED = 1.5A to 46.88 mA
4
µs
IOS
ILED Overshoot in External
Indicator Mode
8
%
3.72
0 mA to ITORCH
A
mV
ENABLE, STROBE, TORCH, TX Voltage Specifications
VIL
Input Logic Low
VIH
Input Logic High
2.5V ≤ VIN ≤ 5.5V
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
t1
SCL Clock Frequency
2.4
t2
Data In Setup Time to SCL High
100
t3
Data Out Stable After SCL Low
0
t4
SDA Low Setup Time to SCL Low
(Start)
100
t5
SDA High Hold Time After SCL
High (Stop)
100
(1)
(2)
6
2.5V ≤ VIN ≤ 4.2V
0
0.4
1.2
VIN
ILOAD = 3 mA
400
V
mV
µs
ns
All voltages are with respect to the potential at the GND pin.
Min and Max limits are specified by design, test, or statistical analysis. Typical (typ.) numbers are not verified, but do represent the most
likely norm. Unless otherwise specified, conditions for typical specifications are: VIN = 3.6V and TA = +25°C.
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t1
SCL
t5
t4
SDA_IN
t2
SDA_OUT
t3
Figure 3. I2C-Compatible Interface Specifications
TYPICAL PERFORMANCE CHARACTERISTICS
Flash LED Current vs. VIN
VLED = 3.6V, ILED = 1.5A
Flash LED Efficiency vs. VIN
VLED = 3.6V, ILED = 1.5A
1.60
100
EFFLED(%)
ILED(A)
1.50
1.45
TA = -40°C
TA = +25°C
TA = +85°C
90
1.55
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)
2.7
Figure 4.
3.1
3.5
3.9 4.3
VIN(V)
4.7
5.1
5.5
Figure 5.
Flash LED Efficiency vs. Flash LED Current
VLED = 3.8V
Torch LED Current vs. VIN
VLED = 3V, ILED = 375mA
100
0.400
96
0.393
92
0.385
0.378
84
ILED(A)
EFFLED(%)
88
80
76
72
68
0.370
VIN =4.2V
VIN =3.9V
VIN =3.6V
VIN =3.3V
VIN =3.0V
VIN =2.7V
0.363
0.355
64
0.348
60
TA=25°C
TA=85°C
TA=-40°C
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)
Figure 6.
Figure 7.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Torch LED Efficiency vs. Vin
VLED = 3V
Iq Standby vs. VIN
EN = 1.8V
3.0
100
2.5
90
IQ STANDBY ( A)
LED EFFICIENCY (%)
95
85
80
75
70
65
TA=25°C
TA=85°C
TA=-40°C
60
55
2.0
1.5
1.0
0.5
50
25°C
85°C
- 40°C
0.0
2.7 3.1 3.4 3.8 4.1 4.5 4.8 5.2 5.5
VIN (V)
2.7
3.1
3.5
Figure 8.
3.9 4.3
VIN (V)
4.7
5.1
5.5
Figure 9.
Iq Shutdown vs. VIN
EN = 0V
Variation of OVP with VIN
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
5.10
3.1
3.5
3.9
4.3
4.7
5.1
2.7
VIN (V)
3.1
3.5
3.9 4.3
VIN (V)
4.7
5.1
Figure 10.
Figure 11.
Frequency with VIN and Over-Temperature
Input Current Limit
Over-Temperature and VIN
Current Limit = 1.7A
PEAK INPUT CURRENT (A)
SWITCHING FREQUENCY (MHz)
4.133
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
5.5
1.92
4.150
3.0
3.3
3.6
3.9
VIN (V)
4.2
25°C
- 40°C
85°C
1.88
1.84
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
Figure 12.
8
25°C
85°C
- 40°C
5.12
-40°C
0.001
2.7
5.18
Figure 13.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Input Current Limit
Over-Temperature and VIN
Current Limit = 1.9A
Input Current Limit
Over-Temperature and VIN
Current Limit = 2.5A
3.1
25°C
- 40°C
85°C
2.25
2.20
PEAK INPUT CURRENT (A)
PEAK INPUT CURRENT (A)
2.30
2.15
2.10
2.05
2.00
1.95
3.0
2.9
25°C
- 40°C
85°C
2.8
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)
Figure 14.
Figure 15.
Input Current Limit
Over-Temperature and VIN
Current Limit = 3.1A
Startup Plot with part in Boost Mode
Current Limit = 1.7A
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
VOUT
3.40
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
Figure 16.
Figure 17.
Strobe with Edge-Triggered Signal (400ms)
Strobe with Level-Triggered Signal (400ms)
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
100ms/DIV
100 ms/DIV
Figure 18.
Figure 19.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Input Voltage Flash Monitor
Report Mode with Default Settings
Internal Indicator Operation
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 20.
Figure 21.
Input Voltage Flash Monitor
Stop and Hold Mode with Default Settings
Input Voltage Flash Monitor
Down Mode with Default Settings
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 22.
Figure 23.
Input Voltage Flash Monitor
Up and Down Mode with Default Settings
Input Voltage Flash Monitor, Up and Down Mode
(0mv Hysteresis, 1/2 Step Filter Time)
VIN
200 mV/
DIV
VIN
200 mV/
DIV
1A/DIV
1A/DIV
ILED
ILED
1A/DIV
1A/DIV
IIN
IIN
400 s/DIV
400 s/DIV
Figure 24.
10
Figure 25.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Input Voltage Flash Monitor, Up and Down Mode
(0mv Hysteresis, 512 µs Filter Time)
Input Voltage Flash Monitor, Up and Down Mode
(256µs Flash Ramp, 1/2 Step Filter Time)
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
Figure 26.
Figure 27.
Impact on LED Current with a TX Event
Time Taken for LM3556 to Ramp
from Torch to Flash after TX Event
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 28.
Figure 29.
Transient Plot when VIN Stepped
from 3 → 2.9V
VIN
200 mV/
DIV
ILED
200 mA/
DIV
40 s/DIV
Figure 30.
LM3556 GENERAL INFORMATION
The LM3556 is a high-power white LED flash driver capable of delivering up to 1.5A 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 2.5V to 5.5V 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 + 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 x RPMOS) and the voltage across the
LED is dropped across the current source.
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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 (typ.) 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 Timeout 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 over-temperature
condition, LED failure (open/short), device thermal shutdown, TX interrupt, and VIN under-voltage conditions.
Startup (Enabling the Device)
Turn on of the LM3556 Torch and Flash modes can be done through the Enable Register (0x0A). On startup,
when VOUT is less than VIN the internal synchronous PFET turns on as a current source and delivers 200 mA
(typ.) to the output capacitor. During this time the current source (LED) is off. When the voltage across the output
capacitor reaches 2.2V (typ.) the current source will turn on. At turn-on the current source will step through each
FLASH or TORCH level until the target LED current is reached. This gives the device a controlled turn-on and
limits inrush current from the VIN supply.
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 turns fully on bringing VOUT up to VIN −
ILEDxRPMOS. In Pass Mode the inductor current is not limited by the peak current limit. In this situation the output
current must be limited to 2A.
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) will ramp up to the programmed Flash current by stepping through all current steps until the programmed
current is reached.
When the part is enabled in Flash Mode through the Enable Register, all mode bits in the Enable Register are
cleared after a flash time-out event.
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.
The following table shows the I2C commands and the state of the mode bits, if the STROBE pin is used to
enable the Flash Mode.
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 will have 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 will have 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 will have to be written to 0x0A.
Part is required to go from External
TORCH Mode to External STROBE
mode using Level Triggered STROBE
0x0A=0x33; 0x07=0xF8
Mode bits are cleared only if the part has an internal flash
time-out event happening before the STROBE level goes
low. To reflash, 0x33 will have to be written to 0x0A. If
the STROBE level goes low before an internal flash timeout event, then mode bits are not cleared.
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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 will ramp 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.
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).
Power Amplifier Synchronization (TX)
The TX pin is a Power Amplifier Synchronization input. This 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 will return 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 will turn 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’.
Input Voltage Flash Monitor (IVFM)
The LM3556 has the ability to adjust the flash current based upon the voltage level present at the IN pin utilizing
an Input Voltage Flash Monitor. Two adjustable thresholds (IVM-D and IVM-U) ranging from 2.9V to 3.6V in 100
mV steps, and four different usage modes (Report Mode, Stop and Hold, Adjust Down Only, Adjust Up and
Down), are provided. The Flags register has the fault flag set when the input voltage crosses the IVM-D value. In
the Report Mode, apart from the fault flag triggering, no action is taken on the LED current. Additionally, the IVMD threshold sets the input voltage boundary that forces the LM3556 to either stop ramping the flash current
during startup (Stop and Hold Mode) or to start decreasing the LED current during the flash (Adjust Down Only
and Adjust Down and Up). 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, please refer to the Input Voltage Flash Monitor (IVFM) Mode Register
(0x01) and Configuration Register (0x07) sections of this datasheet.
Fault Protections
Fault Operation
Upon entering a fault condition, the LM3556 will set 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.
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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 TimeOut 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.
Over-Voltage Protection (OVP)
The output voltage is limited to typically 5.0V (see VOVP Spec). In situations such as an open LED, the LM3556
will raise the output voltage in order to keep the LED current at its target value. When VOUT reaches 5.0V (typ.),
the over-voltage comparator will trip and turn off the internal NFET. When VOUT falls below the “VOVP Off
Threshold”, the LM3556 will begin switching again. The mode bits in the Enable Register (0x0A) are not cleared
upon an OVP.
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 will
terminate the charging phase of the switching cycle.
Since the current limit is sensed in the NMOS switch, there is no mechanism to limit the current when the device
operates in Pass Mode. In Boost mode or Pass Mode if VOUT falls below 2.3V, the part 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.
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 25
µA steps. When an over-temperature 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 will turn on and off during the start and stop of a Flash/Torch/Indicator event. The NTC mode of operation
is set by adjusting the NTC Mode bit in the Configuration Register (0x07). See the NTC Settings Register (0x02)
section for more details. The mode bits in the Enable Register (0x0A) are cleared upon an NTC event.
Under-Voltage Lockout (UVLO)
The LM3556 has an internal comparator that monitors the voltage at IN and will force the LM3556 into shutdown
if the input voltage drops to 2.8V. If the UVLO monitor threshold is tripped, the UVLO flag bit will be set in the
Flags Register (0x0B). If the input voltage rises above 2.8V, the LM3556 will not be available for operation until
there is an I2C read command initiated for the Flags Register (0x0B). Upon a read, the flag register will be
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.
Thermal Shutdown (TSD)
When the LM3556’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) (Thermal Shutdown bit), and the LM3556 will go into standby.
The LM3556 will only be allowed to restart after the Flags Register (0x0B) is read, clearing the fault flag. Upon
restart, if the die temperature is still above +150°C, the LM3556 will reset the Fault flag and re-enter standby.
The mode bits in the Enable Register (0x0A) are cleared upon a TSD.
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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 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 Mode or Torch Mode. An
LED short condition is determined if the voltage at LED goes below 500 mV (typ.) 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.
I2C-COMPATIBLE INTERFACE
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 31. 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.
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 32. Start and Stop Conditions
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.
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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.
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
Figure 33. Write Cycle
w = write (SDA = "0")
r = read (SDA = "1")
ack = acknowledge (SDA pulled down by either master or slave)
id = chip address, 63h for LM3556
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 34. I2C-Compatible Device Address
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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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
Silicon Revision and Filter Time Register (0x00)
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'
Input Voltage Flash Monitor (IVFM) Mode Register (0x01)
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 = 2.9V (default)
001 = 3.0V
010 = 3.1V
011 = 3.2V
100 = 3.3V
101 = 3.4V
110 = 3.5V
111 = 3.6V
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 will stop decreasing once VIN rises above
the IVM-D line + the IVFM hystersis setting. The LM3556 will decrease the current throughout the flash
pulse anytime the input voltage falls below the IVM-D line, and not just once. The flash current will 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 + the IVFM hystersis setting. In this mode, the current will continually adjust 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 2.8V, the LM3556 will enter standby and set 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 35. Stop and Hold Mode
IFLASH
ILED
0 mA
VIN IVM-U
IVM-D
t
tfilter
Figure 36. Adjust Down Only Mode
IFLASH
ILED
0 mA
VIN IVM-U
IVM-D
t
tfilter
tfilter
tfilter
Figure 37. Adjust Up and Down Mode
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NTC Settings Register (0x02)
Bit 7
Bit 6
Bit 5
Bit 4
RFU
RFU
NTC Event
Level
0 = Go to
Standby
(default)
1 = Reduce
to Min Torch
Current
Bit 3
Bit 2
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 1
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 38. NTC Control Block
The TEMP node is connected to an NTC resistor as shown in Figure 38 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].
Indicator Ramp Time Indicator (0x03)
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 = 1.024s
111 = 2.048s
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 = 1.024s
111 = 2.048s
Indicator Blinking Register (0x04)
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
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Indicator Period Count Register (0x05)
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 39. 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 40. Single Pulse with Dead Time
tACTIVE
tPERIOD
tPERIOD
tBLANK
tPERIOD
Figure 41. Multiple Pulse with Dead Time
Torch Ramp Time Register (0x06)
20
Bit 7
Bit 6
RFU
RFU
Bit 5
Bit 4
Bit 3
Torch Ramp-Up Time
000 = 16 ms (default)
001 = 32 ms
010 = 64 ms
011 = 128 ms
100 = 256 ms
101 = 512 ms
110 = 1.024s
111 = 2.048s
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Bit 2
Bit 1
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 = 1.024s
111 = 2.048s
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Configuration Register (0x07)
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 will follow 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 if TX event occurs.
The TX Event Level "Off" setting is designed to only force a shutdown 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 Flags Register (0x0B)) will be set, and the mode bits (bit0 and
bit1 in Enable Register (0x0A)) 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 Enable Register (0x0A)) 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.
Flash Features Register (0x08)
Bit 7
Bit 6
Bit 5
Inductor Current Limit
00 =1.7A
01 = 1.9A
10 = 2.5A
11 = 3.1A (default)
Bit 4
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
Current Control Register (0x09)
Bit 7
RFU
Bit 6
Bit 5
Bit 4
Bit 3
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 2
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)
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Enable Register (0x0A)
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
Bit 1
Bit 0
Mode Bits: M1, M0
00 = Standby (default)
01 = Indicator
10 = Torch
11 = Flash
Enable Register (8 Bits)
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.
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 will remain enabled until
the LM3556 enters the standby state regardless of whether the Pass-Only Mode bit is reset or not during
the following command.
Two-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 will start after I2C-compatible command.
11–Flash Sets Flash Mode with ramping. If Strobe EN = 0, Flash will start after I2C-compatible command.
Flags Register (0x0B)
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 Over-voltage Protection tripped. Open Output cap 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 will only be updated
again if the fault or flags is still present upon a restart.
22
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SNVS796C – AUGUST 2011 – REVISED APRIL 2013
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 42. Control Logic Delays
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 M ode.
2 µs
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23
LM3556
SNVS796C – AUGUST 2011 – REVISED APRIL 2013
www.ti.com
APPLICATION INFORMATION
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.
Larger capacitors such as a 22 µF or capacitors in parallel can be used if lower output voltage ripple is desired.
To estimate the output voltage ripple considering the ripple due to capacitor discharge (ΔVQ) and the ripple due
to the capacitors ESR (ΔVESR) use the following equations:
For continuous conduction mode, the output voltage ripple due to the capacitor discharge is:
ILED x (VOUT - VIN)
'VQ =
fSW x VOUT x COUT
(1)
The output voltage ripple due to the output capacitors ESR 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 2 lists different manufacturers for various output capacitors and
their case sizes suitable for use with the LM3556.
Input Capacitor Selection
Choosing the correct size and type of input capacitor helps minimize the voltage ripple caused by the switching
of the LM3556’s boost converter, and reduces noise on the boost converter's input terminal that can feed through
and disrupt internal analog signals. In the Typical Application Circuit 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) terminal. This reduces
the series resistance and inductance that can inject noise into the device due to the input switching currents. The
table below lists various input capacitors recommended for use with the LM3556.
Table 2. Recommended Input/Output Capacitors (X5R/X7R Dielectric)
Manufacturer
TDK Corporation
TDK Corporation
Part Number
Value
Case Size
Voltage Rating
C1608JB0J106M
10 µF
0603 (1.6 mm × 0.8 mm × 0.8 mm)
6.3V
C2012JB1A106M
10 µF
0805 (2 mm × 1.25 mm × 1.25 mm)
10V
Murata
GRM188R60J106M
10 µF
0603 (1.6 mm x 0.8 mm x 0.8 mm)
6.3V
Murata
GRM21BR61A106KE19
10 µF
0805 (2 mm × 1.25 mm × 1.25 mm)
10V
Inductor Selection
The LM3556 is designed to use a 1 µH or 0.47 µH inductor. The table below lists various inductors and their
manufacturers that work well with the LM3556. When the device is boosting (VOUT > VIN) the inductor will typically
be 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 should 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 the following calculation:
I LOAD VOUT
VIN x (VOUT - VIN)
IPEAK =
K
x
VIN
+ 'IL where 'IL =
2 x f SW x L x VOUT
(3)
where ƒSW = 4 MHz, and efficiency can be found in the Typical Performance Characteristics plots.
24
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SNVS796C – AUGUST 2011 – REVISED APRIL 2013
Table 3. Recommended Inductors
Manufacturer
L
Part Number
Dimensions (L×W×H)
ISAT
RDC
TOKO
1 µH
FDSD0312
3 mm x 3 mm x 1.2 mm
4.5A
43 mΩ
TOKO
1 µH
DFE252010C
2.5 mm × 2 mm × 1 mm
3.4A
60 mΩ
TOKO
1 µH
DFE252012C
2.5 mm × 2 mm × 1.2 mm
3.8A
45 mΩ
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:
30171831
1
1 ·
E§
T °C + 273 298
¹
R(T) = R25°C x e ©
(4)
where β is given in the thermistor datasheet, and R25°C is the thermistor's value at +25°C.
Layout Recommendations
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 LM3556) and as close to the device as possible. The input
capacitor conducts the driver currents during the low-side MOSFET turn-on and turn-off and can see current
spikes over 1A in amplitude. Connecting the input capacitor through short, wide traces to both the IN and
GND terminals will reduce 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 LM3556) and as close as possible to the OUT and GND
terminal. The returns for both CIN and COUT should come together at one point, as close to the GND pin as
possible. Connecting COUT through short, wide traces will reduce the series inductance on the OUT and GND
terminals 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 should 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 should be small so as to reduce the capacitive coupling of the high dV/dt present at SW that can
couple into nearby traces.
4. Avoid routing logic traces near the SW node so as 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 so as to keep the high amplitude LED currents out of the GND plane. For Flash LEDs
that are routed relatively far away from the LM3556, a good approach is to sandwich the forward and return
current paths over the top of each other on two layers. This will help in reducing the inductance of the LED
current paths.
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25
PACKAGE OPTION ADDENDUM
www.ti.com
18-Jan-2013
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package Qty
Drawing
Eco Plan
Lead/Ball Finish
(2)
MSL Peak Temp
Samples
(3)
(Requires Login)
LM3556TME/NOPB
ACTIVE
DSBGA
YFQ
16
250
Green (RoHS
& no Sb/Br)
SNAGCU
Level-1-260C-UNLIM
LM3556TMX/NOPB
ACTIVE
DSBGA
YFQ
16
3000
Green (RoHS
& no Sb/Br)
SNAGCU
Level-1-260C-UNLIM
(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)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
19-Jun-2013
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
LM3556TME/NOPB
DSBGA
YFQ
16
250
178.0
8.4
LM3556TMX/NOPB
DSBGA
YFQ
16
3000
178.0
8.4
Pack Materials-Page 1
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
1.78
1.78
0.69
4.0
8.0
Q1
1.78
1.78
0.69
4.0
8.0
Q1
PACKAGE MATERIALS INFORMATION
www.ti.com
19-Jun-2013
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM3556TME/NOPB
DSBGA
YFQ
LM3556TMX/NOPB
DSBGA
YFQ
16
250
210.0
185.0
35.0
16
3000
210.0
185.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
YFQ0016xxx
D
0.600±0.075
E
TMD16XXX (Rev A)
D: Max = 1.69 mm, Min = 1.63 mm
E: Max = 1.64 mm, Min = 1.58 mm
4215081/A
NOTES:
A. All linear dimensions are in millimeters. Dimensioning and tolerancing per ASME Y14.5M-1994.
B. This drawing is subject to change without notice.
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12/12
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