TI1 LM3554 Synchronous boost converter with 1.2a dual high side led drivers and i2c compatible Datasheet

LM3554
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SNVS549A – JUNE 2009 – REVISED APRIL 2011
LM3554 Synchronous Boost Converter with 1.2A Dual High Side LED Drivers and I2CCompatible Interface
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FEATURES
1
•
•
2
•
•
•
•
•
•
•
•
•
Dual High Side Current Sources
Grounded Cathode Allowing for Better Heat
Sinking and LED Routing
>90% Efficiency
Ultra-Small Solution Size: < 23mm2
Four Operating Modes: Torch, Flash, LED
Indicator and Voltage Output
Accurate and Programmable LED Current from
37.5mA to 1.2A
Programmable 4.5V or 5.0V Constant Output
Voltage
Hardware Flash and Torch Enable
LED Thermal Sensing and Current Scaleback
Software Selectable Input Voltage Monitor
Programmable Flash Timeout
•
•
•
•
•
Dual Synchronization Inputs for RF Power
Amplifier Pulse Events
Open and Short LED Detection
Active High Hardware Enable for Protection
Against System Faults
400kHz I2C-Compatible Interface
16-Bump (1.7mm × 1.7mm × 0.6mm) micro
SMD
APPLICATIONS
•
•
•
Camera Phone LED Flash Controller
Class D Audio Amplifier Power
LED Current Source Biasing
DESCRIPTION
The LM3554 is a 2MHz fixed frequency, current mode synchronous boost converter. The device is designed to
operate as a dual 600mA (1.2A total) constant-current driver for high-current white LEDs, or as a regulated 4.5V
or 5V voltage source.
The dual high-side current sources allow for grounded cathode LED operation. An adaptive regulation method
ensures the current source for each LED remains in regulation and maximizes efficiency.
The main features include: an I2C-compatible interface for controlling the LED current or the desired output
voltage, a hardware Flash enable input for direct triggering of the Flash pulse, and dual TX inputs which force the
Flash pulse into a low-current Torch mode allowing for synchronization to RF power amplifier events or other
high-current conditions. Additionally, an active high hardware enable (HWEN) input provides a hardware
shutdown during system software failures.
Five protection features are available within the LM3554 including a software selectable input voltage monitor, an
internal comparator for interfacing with an external temperature sensor, four selectable current limits to ensure
the battery current is kept below a predetermined peak level, an over-voltage protection feature to limit the output
voltage during LED open circuits, and an output short circuit protection which limits the output current during
shorts to GND. Additionally, the device provides various fault indicators including: a thermal fault flag indicating
the LED temperature has tripped the thermal threshold, a flag indicating a TX event has occurred, a flag
indicating the flash timeout counter has expired, a flag indicating the devices die temperature has reached the
thermal shutdown threshold, and a flag indicating an open or short LED.
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.
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LM3554
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Typical Application Circuits
2.2 PH
4.5V or 5V DC Power Rail
SW
.5V ± 5.5V
IN
OUT
4.7 PF
HWEN
SCL
SDA
LM3554
4.7 PF
VBIAS
LED1
LED2
STROBE
TX1/TORCH/
LEDI/NTC
GPIO1
ENVM/TX2
/GPIO GND
D2
Flash
LEDs
D1
Indicator
LED
RBIAS
2 k:
Thermistor
0.1 PF
5.1 mm
4.5 mm
HWEN
ENVM/TX2/GPIO2
/TORCH/GPIO1
Figure 1. Example Layout
Application Circuit Component List
2
Component
Manufacturer
Value
Part Number
Size (mm)
Rating
L
TOKO
2.2µH
FDSE0312-2R2M
3×3×1.2
2.3A(0.2Ω)
COUT
Murata
4.7µF/10µF
GRM188R60J475M,
or
GRM188R60J106M
1.6×0.8×0.8 (0603)
6.3V
CIN
Murata
4.7µF
GRM185R60J475M
1.6×0.8×0.8 (0603)
6.3V
LEDs
Lumiled
LXCL-PWF4
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Connection Diagram
Top View
A1
A2
A3
A4
B1
B2
B3
B4
C1
C2
C3
C4
D1
D2
D3
D4
Pin Functions
Pin Descriptions
Pin
Name
A1
LED1
High-Side Current Source Output for Flash LED.
A2, B2
OUT
Step-Up DC/DC Converter Output.
A3, B3
SW
Drain Connection for Internal NMOS and Synchronous PMOS Switches.
A4, B4
GND
Ground
LED2
High-Side Current Source Output for Flash LED.
B1
C1
C2
LEDI/NTC
STROBE
C4
IN
D2
Configurable as a High-Side Current Source Output for Indicator LED or Threshold Detector for LED
Temperature Sensing.
TX1/TORCH/GPIO Configurable as a RF Power Amplifier Synchronization Control Input (TX1), a Hardware Torch
1
Enable (TORCH), or a programmable general-purpose logic Input/Output (GPIO1).
C3
D1
Function
Active High Hardware Flash Enable. Drive STROBE high to turn on Flash pulse.
Input Voltage Connection. Connect IN to the input supply, and bypass to GND with a minimum
4.7µF ceramic capacitor.
ENVM/TX2/GPIO2 Configurable as an Active High Voltage Mode Enable (ENVM), Dual Polarity Power Amplifier
/INT
Synchronization Input (TX2), or Programmable General Purpose Logic Input/Output (GPIO2).
SDA
Serial Data Input/Output.
D3
SCL
Serial Clock Input.
D4
HWEN
Active Low Hardware Reset.
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.
Absolute Maximum Ratings
(1) (2)
VIN, VSW, VOUT
-0.3V to 6V
VSCL, VSDA, VHWEN, VSTROBE, VTX1/TORCH, VENVM/TX2, VLED1, VLED2, VLEDI/NTC
Continuous Power Dissipation (3)
-0.3V to to (VIN+0.3V) w/ 6.0V max
Internally Limited
Junction Temperature (TJ-MAX)
+150°C
Storage Temperature Range
-65°C to +150°C
(4)
Maximum Lead Temperature (Soldering)
(1)
(2)
(3)
(4)
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under
which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed
performance limits and associated test conditions, see the Electrical Characteristics table.
All voltages are with respect to the potential at the GND pin.
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.).
For detailed soldering specifications and information, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer
Level chip Scale Package (AN-1112)
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Operating Ratings
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(1) (2)
VIN
2.5V to 5.5V
Junction Temperature (TJ)
Ambient Temperature (TA)
(1)
(2)
(3)
-30°C to +125°C
(3)
-30°C to +85°C
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under
which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed
performance limits and associated test conditions, see the Electrical Characteristics table.
All voltages are with respect to the potential at the GND pin.
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
Junction-to-Ambient Thermal Resistance (θJA), TMD16 Package (1)
(1)
60°C/W
Junction-to-ambient thermal resistance (θJA) is taken from a thermal modeling result, performed under the conditions and guidelines set
forth in the JEDEC standard JESD51-7. The test board is a 4-layer FR-4 board measuring 102mm x 76mm x 1.6mm with a 2x1 array of
thermal via's. The ground plane on the board is 50mm x 50mm. Thickness of copper layers are 36µm/18µm/18µm/36µm
(1.5oz/1oz/1oz/1.5oz). Ambient temperature in simulation is 22°C, still air. Power dissipation is 1W.
Electrical Characteristics
Limits in standard typeface are for TA = +25°C. Limits in boldface type apply over the full operating ambient temperature
range (-30°C ≤ TA ≤ +85°C). Unless otherwise specified, VIN = 3.6V, VHWEN = VIN. (1) (2)
Symbol
Parameter
Conditions
Min
Typ
Max
ILED1+ILED2
1128
1200
1284
ILED1 or ILED2
541
600
657
Units
Current Source Specifications
ILED
VHR
IMATCH
Current Source
Accuracy
600mA Flash
LED Setting,
VOUT = VIN
17mA Torch
Current Setting, ILED1+ILED2
VHR = 500mV
mA
30.4
33.8
37.2
Current Source
Regulation
600mA setting, VOUT = 3.75V
Voltage (VOUT VLED)
300
mV
LED Current
Matching
0.35
%
600mA setting, VLED = 3.2V
Step-Up DC/DC Converter Specifications
(1)
(2)
(3)
4
VREG
Output Voltage
Accuracy
2.7V ≤ VIN ≤ 4.2V, IOUT = 0mA,
VENVM = VIN, OV bit = 0
4.8
5
5.2
Output OverVoltage
Protection Trip
Point (3)
On Threshold, 2.7V ≤ VIN ≤ 5.5V
5.4
5.6
5.7
VOVP
RPMOS
RNMOS
V
V
Off Threshold
5.3
PMOS Switch
On-Resistance
IPMOS = 1A
150
mΩ
NMOS Switch
On-Resistance
INMOS = 1A
150
mΩ
All voltages are with respect to the potential at the GND pin.
Min and Max limits are guaranteed by design, test, or statistical analysis. Typical (Typ) numbers are not guaranteed, but do represent
the most likely norm. Unless otherwise specified, conditions for typical specifications are: VIN = 3.6V and TA = +25°C.
The typical curve for Over-Voltage Protection (OVP) is measured in closed loop using the typical application circuit . The OVP value is
found by forcing an open circuit in the LED1 and LED2 path and recording the peak value of VOUT. The value given in the Electrical
Table is found in an open loop configuration by ramping the voltage at OUT until the OVP comparator trips. The closed loop data can
appear higher due to the stored energy in the inductor being dumped into the output capacitor after the OVP comparator trips. At worst
case is an open circuit condition where the output voltage can continue to rise after the OVP comparator trips by approximately
IIN×sqrt(L/COUT).
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Electrical Characteristics (continued)
Limits in standard typeface are for TA = +25°C. Limits in boldface type apply over the full operating ambient temperature
range (-30°C ≤ TA ≤ +85°C). Unless otherwise specified, VIN = 3.6V, VHWEN = VIN. (1) (2)
Symbol
Parameter
ICL
Switch Current
Limit (4)
IOUT_SC
Output Short
Circuit Current
Limit
ILED/NTC
Indicator
Current
Min
Typ
Max
CL bits = 00
Conditions
0.711
1.05
1.373
CL bits = 01
1.295
1.51
1.8
CL bits = 10
1.783
1.99
2.263
CL bits = 11
2.243
2.45
2.828
VOUT < 2.3V
LEDI/NTC bit =
0
550
IND1, IND0 bits
= 00
2.3
IND1, IND0 bits
= 01
4.6
IND1, IND0 bits
= 10
6.9
IND1, IND0 bits
= 11
8.2
Units
A
mA
mA
Comparator
Trip Threshold
LEDI/NTC bit = 1, 2.7V ≤ VIN ≤
5.5V
0.947
1.052
1.157
V
Switching
Frequency
2.7V ≤ VIN ≤ 5.5V
1.75
2
2.23
MHz
IQ
Quiescent
Supply Current
Device Not Switching
630
ISHDN
Shutdown
Supply Current
2.7V ≤ VIN ≤ 5.5V
3.5
tTX
Flash-to-Torch
LED Current
Settling Time
TX_ Low to High, ILED1 + ILED2 =
1.2A to 180mA
20
VIN_TH
VIN Monitor
Trip Threshold
VIN Falling, VIN Monitor Register
= 0x01 (Enabled with VIN_TH =
3.1V)
VTRIP
fSW
2.95
3.09
µA
6.6
µA
µs
3.23
V
0
0.4
V
1.2
VIN
V
400
mV
TX1/TORCH/GPIO1, STROBE, HWEN, ENVM/TX2/GPIO2 Voltage Specifications
VIL
Input Logic Low 2.7V ≤ VIN ≤ 5.5V
VIH
Input Logic
High
2.7V ≤ VIN ≤ 5.5V
VOL
Output Logic
Low
ILOAD = 3mA, 2.7V ≤ VIN ≤ 5.5V
RTX1/TORCH
Internal Pulldown
Resistance at
TX1/TORCH
300
kΩ
RSTROBE
Internal PullDown
Resistance at
STROBE
300
kΩ
I2C-Compatible Voltage Specifications (SCL, SDA)
(4)
VIL
Input Logic Low 2.7V ≤ VIN ≤ 5.5V
VIH
Input Logic
High
2.7V ≤ VIN ≤ 5.5V
VOL
Output Logic
Low (SCL)
ILOAD = 3mA, 2.7V ≤ VIN ≤ 5.5V
0
0.4
V
1.22
VIN
V
400
mV
The typical curve for Current Limit is measured in closed loop using the typical application circuit by increasing IOUT until the peak
inductor current stops increasing. The value given in the Electrical Table is measured open loop and is found by forcing current into SW
until the current limit comparator threshold is reached. Closed loop data appears higher due to the delay between the comparator trip
point and the NFET turning off. This delay allows the closed loop inductor current to ramp higher after the trip point by approximately
20ns × VIN/L
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Electrical Characteristics (continued)
Limits in standard typeface are for TA = +25°C. Limits in boldface type apply over the full operating ambient temperature
range (-30°C ≤ TA ≤ +85°C). Unless otherwise specified, VIN = 3.6V, VHWEN = VIN. (1) (2)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
I2C-Compatible Timing Specifications (SCL, SDA) — See Figure 1
1/t1
SCL Clock
Frequency
t2
Data In Setup
Time to SCL
High
t3
Data Out
Stable After
SCL Low
t4
t5
400
kHz
100
ns
0
ns
SDA Low Setup
Time to SCL
Low (Start)
160
ns
SDA High Hold
Time After SCL
High (Stop)
160
ns
t1
SCL
t5
t4
SDA_IN
t2
SDA_OUT
t3
Figure 2. I2C Timing
6
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Typical Performance Characteristics
VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL = 0.15Ω), TA = +25°C unless
otherwise specified.
LED Efficiency
vs
VIN
(Single LED, L = TOKO FDSE0312-2R2)
LED Efficiency
vs
VIN
(Dual LEDs, L = TOKO FDSE0312-2R2)
Input Current
vs
VIN
(Single LED, L = TOKO FDSE0312-2R2)
LED Efficiency
vs
VIN
(Single LED, L = Coilcraft LPS4018-222)
LED Efficiency
vs
VIN
(Dual LED's, L = Coilcraft LPS4018-222)
Input Current
vs
VIN
(Single LED, L = Coilcraft LPS4018-222)
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL = 0.15Ω), TA = +25°C unless
otherwise specified.
(1)
8
Efficiency
vs
IOUT
(Voltage Output Mode, VOUT = 5V)
Efficiency
vs
VIN
(Voltage Output Mode, VOUT = 5V)
VOUT
vs
IOUT
(Voltage Output Mode, VOUT = 5V)
VOUT
vs
VIN
(Voltage Output Mode, VOUT = 5V)
Torch Current Matching
vs
Code
(VIN= 3.6V, VLED1, VLED2 = 3.2V,
TA = -40°C to +85°C, (1) )
Torch Current
vs
VIN
(VLED1, VLED2 = 3.2V, TA = +25°C, 75mA setting)
Current Matching = Absolute Value((ILED1 - ILED2)/(ILED1 + ILED2)) × 100
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL = 0.15Ω), TA = +25°C unless
otherwise specified.
Torch Current
vs
VIN
(VLED1, VLED2 = 3.2V, TA = +85°C, 75mA setting)
Torch Current
vs
VIN
(VLED1, VLED2 = 3.2V, TA = −40°C, 75mA setting)
Flash Current Matching
vs
Code
(VIN= 3.6V, VLED1, VLED2 = 3.2V,
TA = -40°C to +85°C, (1)
Flash Current
vs
VIN
(VLED1, VLED2 = 3.2V, TA = +25°C, 600mA setting)
Flash Current
vs
VIN
(VLED1, VLED2 = 3.2V, TA = +85°C, 600mA setting)
Flash Current
vs
VIN
(VLED1, VLED2 = 3.2V, TA = -40°C, 600mA setting)
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL = 0.15Ω), TA = +25°C unless
otherwise specified.
Switching Frequency
vs
VIN
Shutdown Current
vs
VIN
(VHWEN = 0V)
Active (Non-Switching) Supply Current
vs
VIN
(VLED = 1.5V)
Active (Switching) Supply Current
vs
VIN
(VOUT = 5V, IOUT = 400mA)
Closed Loop Current Limit
vs
VIN
(Flash Duration Register bits [6:5] = 00,
(2)
10
(2)
)
Closed Loop Current Limit
vs
VIN
(Flash Duration Register bits [6:5] = 01,
(2)
)
The typical curve for Over-Voltage Protection (OVP) is measured in closed loop using the typical application circuit . The OVP value is
found by forcing an open circuit in the LED1 and LED2 path and recording the peak value of VOUT. The value given in the Electrical
Table is found in an open loop configuration by ramping the voltage at OUT until the OVP comparator trips. The closed loop data can
appear higher due to the stored energy in the inductor being dumped into the output capacitor after the OVP comparator trips. At worst
case is an open circuit condition where the output voltage can continue to rise after the OVP comparator trips by approximately
IIN×sqrt(L/COUT).
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL = 0.15Ω), TA = +25°C unless
otherwise specified.
Closed Loop Current Limit
vs
VIN
(Flash Duration Register bits [6:5] = 10,
(2)
)
Closed Loop Current Limit
vs
VIN
(Flash Duration Register bits [6:5] = 11,
(2)
)
VIN Monitor Thresholds
vs
Temperature
OVP Thresholds
vs
VIN
Short Circuit Current Limit
vs
VIN
Indicator Current
vs
VIN, VLEDI = 2V
(Torch Brightness Register bits[7:6] = 00)
(3)
(3)
The typical curve for Current Limit is measured in closed loop using the typical application circuit by increasing IOUT until the peak
inductor current stops increasing. The value given in the Electrical Table is measured open loop and is found by forcing current into SW
until the current limit comparator threshold is reached. Closed loop data appears higher due to the delay between the comparator trip
point and the NFET turning off. This delay allows the closed loop inductor current to ramp higher after the trip point by approximately
20ns × VIN/L
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL = 0.15Ω), TA = +25°C unless
otherwise specified.
Indicator Current
vs
VIN, VLEDI = 2V
(Torch Brightness Register bits[7:6] = 01)
Indicator Current
vs
VIN, VLEDI = 2V
(Torch Brightness Register bits[7:6] = 10)
Indicator Current
vs
VIN, VLEDI = 2V
(Torch Brightness Register bits[7:6] = 11)
NTC Comparator Trip Threshold
vs
VIN
Startup into Flash Mode
Single LED
IFLASH = 1.2A
Startup into Torch Mode
Single LED, Hardware Torch Mode, 90mA Torch Setting
ITORCH = 180mA
Channel 1: VOUT (2V/div)
Channel 4: ILED (500mA/div)
Channel 2: IL (500mA/div)
Channel 3: STROBE (5V/div)
Time Base: (100µs/div)
12
Channel 1: VOUT (2V/div)
Channel 4: ILED (100mA/div)
Channel 2: IL (500mA/div)
Channel 3: TX1 (5V/div)
Time Base: (100µs/div)
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL = 0.15Ω), TA = +25°C unless
otherwise specified.
Torch Mode to Flash Mode Transition
Single LED
ITORCH = 295mA, IFLASH = 1.2A
TX1 Interrupt Operation, TX1 Rising
Single LED
IFLASH = 1.2A, ITORCH = 180mA
Channel 1: VOUT (5V/div)
Channel 4: ILED (500mA/div)
Channel 2: IL (1A/div)
Channel 3: STROBE (5V/div)
Time Base: (100µs/div)
TX1 Interrupt Operation, TX1 Falling
Single LED
IFLASH = 1.2A, ITORCH = 180mA
Channel 1: VOUT (2V/div)
Channel 4: ILED (500mA/div)
Channel 2: IL (1A/div)
Channel 3: TX1 (5V/div)
Time Base: (20µs/div)
Channel 1: VOUT (2V/div)
Channel 4: ILED (500mA/div)
Channel 2: IL (1A/div)
Channel 3: TX1 (5V/div)
Time Base: (20µs/div)
Channel 3: VIN (1V/div)
Channel 4: ILED (500mA/div)
Channel 2: IL (1A/div)
Time Base: (400µs/div)
Line Transient
(LED Mode, Single LED, IFLASH = 1.2A)
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL = 0.15Ω), TA = +25°C unless
otherwise specified.
Load Transient
VIN = 3.6V
(Voltage Output Mode, VOUT = 5V)
Line Transient
IOUT = 500mA
(Voltage Output Mode, VOUT = 5V)
Channel 1: VOUT (500mV/div, AC Coupled)
Channel 4: IOUT (200mA/div)
Channel 2: IL (500mA/div)
Time Base: (40µs/div)
Flash Pulse to HWEN Low
Single LED, ILED = 1.2A
Channel 3 (Top Trace): VIN (1V/div)
Channel 1: VOUT (100mV/div, AC Coupled)
Channel 2: IL + IIN (500mA/div)
Time Base: (200µs/div)
Flash Pulse to Flash Pulse + VOUT Mode
Single LED, ILED = 1.2A, VOUT = 5V
Channel 1: VOUT (2V/div)
Channel 4: ILED (500mA/div)
Channel 2: IL (1A/div)
Channel 3: HWEN (5V/div)
Time Base: (20µs/div)
Channel 1: VOUT (2V/div)
Channel 4: ILED (500mA/div)
Channel 2: IL (1A/div)
Channel 3: ENVM (5V/div)
Time Base: (100µs/div)
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL = 0.15Ω), TA = +25°C unless
otherwise specified.
Flash Pulse + VOUT to Flash Pulse
Single LED, ILED = 1.2A, VOUT = 5V
NTC Mode Response
Single LED, ILED = 1.2A
Circuit of Figure 28 (R(T) = 100kΩ (@+25°C), R3 = 9kΩ)
Channel 3: NTC Pin Voltage (500mV/div)
Channel 4: ILED (500mA/div)
Time Base: (200ms/div)
Channel 1: VOUT (2V/div)
Channel 4: ILED (500mA/div)
Channel 2: IL (1A/div)
Channel 3: ENVM (5V/div)
Time Base: (100µs/div)
VIN Monitor Response
Single LED, ILED = 1.2A
3.1V UVLO Setting
Channel 3: VIN (1V/div)
Channel 4: ILED (500mA/div)
Time Base: (100ms/div)
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Block Diagram
SW
Over Voltage
Comparator
+
-
IN
2 MHz
Oscillator
VREF
150 m:
VREF
OUT
ILED1
ILED2
PWM
Control
ILEDI
150 m:
LEDI/
NTC
Thermal
Shutdown
+150oC
Error
Amplifier
+
-
ISET
LED1
Reference
Mode
Select
LED2
VREF
+
+
-
Current
Sense/Current
Current
Limit
Sense/Current
Limit
VTRIP
Feedback
Mode
Select
Max
VLED
Slope
Compensation
SDA
I2C
Interface
SCL
HWEN
Control
Logic/
Soft-Start
TX1/TORCH/
GPIO1
STROBE
ENVM/TX2/
GPIO2
GND
Overview
The LM3554 is a high-power white LED flash driver capable of delivering up to 1.2A of LED current into a single
LED, or up to 600mA into two parallel LEDs. The device incorporates a 2MHz constant frequency, synchronous,
current mode PWM boost converter, and two high-side current sources to regulate the LED current over the 2.5V
to 5.5V input voltage range.
The LM3554 operates in two modes: LED mode or constant Voltage Output mode. In LED mode when the output
voltage is greater than VIN – 150mV, the PWM converter switches and maintains at least 300mV (VHR) across
both current sources (LED1 and LED2). This minimum headroom voltage ensures that the current sinks remain
in regulation. When the input voltage is above VLED + VHR, the device operates in Pass mode with the device not
switching and the PFET on continuously. In Pass mode the difference between (VIN - ILED×RON_P) and VLED is
dropped across the current sources. If the device is operating in Pass mode, and VIN drops to a point that forces
the device into switching, the LM3554 will make a one-time decision to jump into switching mode. The LM3554
remains in switching mode until the device is shutdown and re-enabled. This is true even if VIN were to rise back
above VLED + 300mV during the current Flash or Torch cycle. This prevents the LED current from oscillating
when VIN is operating close to VOUT.
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In Voltage Output mode the LM3554 operates as a voltage output boost converter with selectable output
voltages of 4.5V and 5V. In this mode the LM3554 is able to deliver up to typically 5W of output power. At light
loads and in Voltage Output mode the PWM switching converter changes over to a pulsed frequency regulation
mode and only switches as necessary to ensure proper LED current or output voltage regulation. This allows for
improved light load efficiency compared to converters that operate in fixed-frequency PWM mode at all load
currents.
Additional features of the LM3554 include 4 logic inputs, an internal comparator for LED thermal sensing, and a
low-power indicator LED current source. The STROBE input provides a hardware Flash mode enable. The
ENVM/TX2/GPIO2 input is configurable as a hardware Voltage Output mode enable (ENVM), an active high
Flash interrupt that forces the device from FLASH mode to a low-power TORCH mode (TX2), or as a
programmable logic input/output (GPIO2). The TX1 input is configurable as an active high Flash interrupt that
forces the device from FLASH mode to a low-power TORCH mode (TX1), as a hardware Torch mode enable
(TORCH), or as a programmable logic input/output (GPIO1) . The HWEN input provides for an active low
hardware shutdown of the device. Finally, the LEDI/NTC pin is configurable as a low-power indicator LED driver
(LEDI), or as a threshold detector for thermal sensing (NTC). In NTC mode when the threshold (VTRIP) at the
LEDI/NTC pin is crossed (VLEDI/NTC falling), the Flash pulse is forced to the Torch current setting, or into
shutdown depending on the NTC Shutdown bit setting .
Control of the LM3554 is done via an I2C-compatible interface. This includes switch-over from LED to Voltage
Output mode, adjustment of the LED current in TORCH mode, adjustment of the LED current in FLASH mode,
adjustment of the indicator LED currents, changing the flash LED current duration, changing the switch current
limit. Additionally, there are 5 flag bits that can be read back indicating flash current timeout, over-temperature
condition, LED failure (open or short), LED thermal failure, and an input voltage fault.
STARTUP
Turn on of the LM3554 is done through bits [2:0] of the Torch Brightness Register (0xA0), bits [2:0] of the Flash
Brightness Register (0xB0), the ENVM input, or the STROBE input. Bits [1:0] of the Torch Brightness Register or
Flash Brightness Register enables/disables the current sources (LED1, LED2, and LEDI). Bit [2] enables/disables
the voltage output mode. A logic high at STROBE enables Flash mode. A logic high on the ENVM input forces
the LM3554 into Voltage Output mode.
On startup, when VOUT is less than VIN the internal synchronous PFET turns on as a current source and delivers
typically 350mA to the output capacitor. During this time all current sources (LED1, LED2, and LEDI) are off.
When the voltage across the output capacitor reaches 2.2V, the current sources can turn on. At turn-on the
current sources step through each FLASH or TORCH level until the target LED current is reached (16 µs/step).
This gives the device a controlled turn-on and limits inrush current from the VIN supply.
PASS MODE
Once the Output voltage charges up to VIN - 150mV the LM3554 will decide if the part operates in Pass Mode or
Boost mode. If the voltage difference between VOUT and VLED is less than 300mV, the device will transition in
Boost Mode. If the difference between VOUT and VLED is greater than 300mV, the device will operate in Pass
Mode. In Pass Mode the boost converter stops switching, and the synchronous PFET turns fully on bringing VOUT
up to VIN – IIN×RPMOS (RPMOS = 150mΩ). In Pass Mode the inductor current is not limited by the peak current
limit. In this situation the output current must be limited to 2.5A.
LIGHT LOAD DISABLE
Configuration Register 1 bit [0] = 1 disables the light load comparator. With this bit set to 0 (default) the light load
comparator is enabled. Light Load mode only applies when the LM3554 is active in Voltage Output mode. In LED
mode the Light Load Comparator is always disabled. When the light load comparator is disabled the LM3554 will
operate at a constant frequency down to ILOAD = 0. Disabling light load can be useful when a more predictable
switching frequency across the entire load current range is desired.
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VOLTAGE OUTPUT MODE
Bit 2 (VM) of the Torch Brightness Register, bit 2 (VM) of the Flash Brightness Register, or the ENVM input
enables or disables the Voltage Output mode. In Voltage Output mode the device operates as a simple boost
converter with two selectable voltage levels (4.5V and 5V). Write a (1) to bit 1 (OV) of Configuration Register 1 to
set VOUT to 5V. Write a (0) to this bit to set VOUT to 4.5V. In Voltage Output mode the LED current sources can
continue to operate; however, the difference between VOUT and VLED will be dropped across the current sources.
(See MAXIMUM OUTPUT POWER section.) In Voltage Output mode when VIN is greater than VOUT the LM3554
operates in Pass Mode (see PASS MODE section).
At light loads the LM3554 switches over to a pulsed frequency mode operation (light load comparator enabled).
In this mode the device will only switch as necessary to maintain VOUT within regulation. This mode provides a
better efficiency due to the reduction in switching losses which become a larger portion of the total power loss at
light loads.
OVER-VOLTAGE PROTECTION
The output voltage is limited to typically 5.6V (5.7V max). In situations such as the current source open, the
LM3554 will raise the output voltage in order to try and keep the LED current at its target value. When VOUT
reaches 5.6V the over-voltage comparator will trip and turn off both the internal NFET and PFET. When VOUT
falls below 5.4V (typical), the LM3554 will begin switching again.
CURRENT LIMIT
The LM3554 features 4 selectable current limits: 1A, 1.5A, 2A, and 2.5A. These are selectable through the I2Ccompatible interface via bits 5 (CL0) and 6 (CL1) of the Flash Duration Register. When the current limit is
reached, the LM3554 stops switching for the remainder of the switching cycle.
Since the current limit is sensed in the NMOS switch there is no mechanism to limit the current when the device
operates in Pass Mode. In situations where there could potentially be large load currents at OUT, and the
LM3554 is operating in Pass mode, the load current must be limited to 2.5A. In Boost mode or Pass mode if
VOUT falls below approximately 2.3V, the part stops switching, and the PFET operates as a current source
limiting the current to typically 350mA. This prevents damage to the LM3554 and excessive current draw from
the battery during output short circuit conditions.
MAXIMUM LOAD CURRENT (VOLTAGE MODE)
Assuming the power dissipation in the LM3554 and the ambient temperature are such that the device will not hit
thermal shutdown, the maximum load current as a function of IPEAK is:
(I PEAK - 'IL) x K x VIN
I LOAD =
VOUT
(1)
Where η is efficiency and is found in the efficiency curves in the Typical Performance Characteristics and
VIN x (VOUT - VIN )
'IL =
2 x fSW x L x VOUT
(2)
Figure 3 shows the theoretical maximum Output current vs theoretical Efficiency at different input and output
voltages using the previous two equations for ΔIL and ILOAD with a peak current of 2.5A. This plot represents the
theoretical maximum output current (for the LM3554 in Voltage Output mode) that the device can deliver just
before hitting current limit.
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Maximum Output Current (A)
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2.3
2.2
2.1
2
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.6
Maximum Output Current vs Efficiency
(I PEAK = 2.5A)
VIN = 3.6V, VOUT = 4V
VIN = 3V, VOUT = 4V
VIN = 3.6V, VOUT = 5V
VIN = 2.5V, VOUT = 4V
VIN = 3V, VOUT = 5V
VIN = 2.5V, VOUT = 5V
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
Efficiency (POUT / PIN )
Figure 3. LM3554 Maximum Output Current
MAXIMUM OUTPUT POWER
Output power is limited by three things: the peak current limit, the ambient temperature, and the maximum power
dissipation in the package. If the LM3554’s die temperature is below the absolute maximum rating of +125°C, the
maximum output power can be over 6W. However, any appreciable output current will cause the internal power
dissipation to increase and therefore increase the die temperature. This can be additionally compounded if the
LED current sources are operating while the device is in Voltage Output mode since the difference between VOUT
and VLED is dropped across the current sources. Any circuit configuration must ensure that the die temperature
remains below +125°C taking into account the ambient temperature derating.
Maximum Output Power (Voltage Output Mode)
In Voltage Output mode the total power dissipated in the LM3554 can be approximated as:
PDISS = PN + PP + PLED1 + PLED2 + PIND
(3)
PN is the power lost in the NFET, PP is the PFET power loss, PLED1, PLED2, and PIND are the losses across the
current sinks. An approximate calculation of these losses gives:
PDISS =
§(VOUT - VIN ) x VOUT·
©
VIN2
¹
x ILOAD2 x R NFET +
§VOUT·
© VIN ¹
x ILOAD2 x R PFET + (VOUT - VLED ) x ILED + (VOUT - VIND) x I IND
ILOAD = IOUT + ILED + I IND
I LED = ILED1 + I LED2
(4)
The above formulas consider the average current through the NFET and PFET. The actual power losses will be
higher due to the RMS currents and the quiescent power into IN. These, however, can give a decent
approximation.
Maximum Output Power (Led Boost Mode)
In LED mode with VOUT > VIN the LM3554’s boost converter will switch and make VOUT = VLED + 0.3V. In this
situation the total power dissipated in the LM3554 is approximated as:
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PDISS =
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§(VLED + 0.3V - VIN ) x VLED + 0.3V)·
©
VIN
2
¹
x ILOAD2 x R NFET +
§VLED + 0.3V·
©
VIN
¹
x ILOAD2 x R PFET + 0.3V x I LED + (VLED + 0.3V - VIND ) x I IND
ILOAD = ILED + I IND
I LED = ILED1 + I LED2
Figure 4. Equation 1
Maximum Output Power (Led Pass Mode)
In LED mode with VIN – ILOAD × RPFET > VLED + 0.3V, the LM3554 operates in Pass Mode. In this case. the NFET
is off, and the PFET is fully on. The difference between VIN - ILOAD×RPMOS and VLED will be dropped across the
current sources. In this situation the total power dissipated in the LM3554 is approximated as:
PDISS = [ I LOAD2 x R PFET + (VIN - R PFET x I LOAD - VLED ) x I LED + (VIN - R PFET x I LOAD - VIND) x IIND ]
I LOAD = I LED + IIND
I LED = I LED1 + I LED2
Figure 5. Equation 2
Once the total power dissipated in the LM3554 is calculated the ambient temperature and the thermal resistance
of the 16-bump micro SMD (TMD16) are used to calculate the total die temperature (or junction temperature TJ).
As an example, assume the LM3554 is operating at VIN = 3.6V and configured for Voltage Output mode with
VOUT = 5V and IOUT = 0.7A. The LED currents are then programmed in Torch mode with 150mA each at VLED =
3.6V. Additionally, the indicator LED has 10mA at VIND = 3.6V. Using Equations 1 and 2 above, the approximate
total power dissipated in the device is:
PDISS = 139 mW + 357 mW + 420 mW + 14 mW = 930 mW
(5)
The die temperature approximation will be:
TJ = 0. 93 W x 60 °
C
+ 25 °C = 80.8 °C.
W
(6)
In this case the device can operate at these conditions. If then the ambient temperature is increased to +85°C,
the die temperature would be +140.8°C; thus, the die temperature would be above the absolute maximum
ratings, and the load current would need to be scaled back. This example demonstrates the steps required to
estimate the amount of current derating based upon operating mode, circuit parameters, and the device's
junction-toambient thermal resistance. In this example a thermal resistance of 60°C/W was used (JESD51-7
standard). Since thermal resistance from junction-to-ambient is largely PCB layout dependent, the actual number
used will likely be different and must be taken into account when performing these calculations.
FLASH MODE
In Flash mode the LED current sources (LED1 and LED2) each provide 16 different current levels from typically
34mA to approximately 600mA. The Flash currents are set by writing to bits [6:3] of the Flash Brightness
Resister. Flash mode is activated by either writing a (1, 1) to bits [1:0] of the Torch Brightness Register, writing a
(1,1) to bit [1:0] of the Flash Brightness Register, or by pulling the STROBE pin high. Once the Flash sequence
is activated, both current sinks (LED1 and LED2) will ramp up to the programmed Flash current by stepping
through all Flash levels (16µs/step) until the programmed current is reached.
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FLASH TERMINATION (STROBE-INITIATED FLASH)
Bit [7] of the Flash Brightness Register (STR bit) determines how the Flash pulse terminates with STROBEinitated flash pulses. With the STR bit = 1 the Flash current pulse will only terminate by reaching the end of the
Flash Timeout period. With STR = 0, Flash mode can be terminated by pulling STROBE low, or by allowing the
Flash Timeout period to elapse. If STR = 0 and STROBE is toggled before the end of the Flash Timeout period,
the Timeout period resets on the rising edge of STROBE. See LM3554 TIMING DIAGRAMS regarding the Flash
pulse termination for the different STR bit settings.
After the Flash pulse terminates, either by a flash timeout, or pulling STROBE low, LED1 and LED2 turn
completely off. This happens even when Torch is enabled via the I2C-compatible interface, and the Flash pulse is
turned on by toggling STROBE. After a Flash event ends the EN1, EN0 bits (bits [1:0] of the Torch Brightness
Register, or Flash Brightness Register) are automatically re-written with (0, 0).
FLASH TERMINATION (I2C-INITIATED FLASH)
For I2C initated flash pulses, the flash LED current can be terminated by either waiting for the timeout duration to
expire or by writing a (0, 0) to bits [1:0] of the Torch Brightness Register, or Flash Brightness Register. If the
timeout duration is allowed to elapse, the flash enable bits of the Torch Brightness and Flash Brightness
Registers are automatically reset to 0.
FLASH TIMEOUT
The Flash Timeout period sets the duration of the flash current pulse. Bits [4:0] of the Flash Duration Register
programs the 32 different Flash Timeout levels in steps of 32ms giving a Flash Timeout range of 32ms to
1024ms (see Table 7).
TORCH MODE
In Torch mode the current sources LED1 and LED2 each provide 8 different current levels (see Table 2). The
Torch currents are adjusted by writing to bits [5:3] of the Torch Brightness Register. Torch mode is activated by
setting Torch Brightness Register bits [1:0] to (1, 0) or Flash Brightness bits [1:0] to (1, 0). Once the Torch mode
is enabled the current sources will ramp up to the programmed Torch current level by stepping through all of the
Torch currents at 16µs/step until the programmed Torch current level is reached.
TX1/TORCH
The TX1/TORCH/GPIO1 input has a triple function. With Configuration Register 1 Bit [7] = 0 (default),
TX1/TORCH/GPIO1 is a Power Amplifier Synchronization input (TX1 mode). This is designed to reduce the
current pulled from the battery during an RF power amplifier transmit event. When the LM3554 is engaged in a
Flash event, and the TX1 pin is pulled high, both LED1 and LED2 are forced into Torch mode at the programmed
Torch current setting. If the TX1 pin is then pulled low before the Flash pulse terminates the LED current will
ramp back to the previous Flash current level. At the end of the Flash timeout whether the TX1 pin is high or low,
the LED current will turn off.
With the Configuration Register Bit [7] = 1, TX1/TORCH/GPIO1 is configured as a hardware Torch mode enable
(TORCH). In this mode a high at TORCH turns on the LED current sources in Torch mode. STROBE (or I2initiated flash) will take precedence over the TORCH mode input. Figure 15 details the functionality of the
hardware TORCH mode. Additionally, when a flash pulse is initiated during hardware TORCH mode, the
hardware torch mode bit is reset at the end of the flash pulse. In order to re-enter hardware Torch mode, bit [7] of
Configuration Register 1 would have to be re-written with a 1.
The TX1/TORCH/GPIO1 input can also be configured as a GPIO input/output. for details on this, refer to the
GPIO REGISTER ection of the datasheet.
ENVM/TX2/GPIO2
The ENVM/TX2/GPIO2/INT pin has four functions. In ENVM mode (Configuration Register 1 bit [5] = 0), the
ENVM/TX2/GPIO2/INT pin is an active high logic input that forces the LM3554 into Voltage Output Mode. In TX2
mode (Configuration Register 1 bit [5] = 1), the ENVM/TX2/GPIO2/INT pin is a Power Amplifier Synchronization
input that forces the LM3554 from Flash mode into Torch mode. In GPIO2 mode (GPIO Register Bit [3] = 1) the
ENVM/TX2/GPIO2/INT pin is configured as a general purpose logic input/output and controlled via bits[3:5] of the
GPIO Register. In INT mode the ENVM/TX2/GPIO2/INT pin is a hardware interrupt output which pulls low when
the LM3554 is in NTC mode, and the voltage at LEDI/NTC falls below VTRIP.
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In TX2 mode, when Configuration Register 1 bit [6] = 0 the ENVM/TX2/GPIO2 pin is an active low transmit
interrupt input. Under this condition, when the LM3554 is engaged in a Flash event, and ENVM/TX2/GPIO2 is
pulled low, both LED1 and LED2 are forced into either Torch mode or LED shutdown depending on the logic
state of Configuration Register 2 bit [0]. In TX2 mode with Configuration Register 1 bit [6] = 1, the
ENVM/TX2/GPIO2 pin is an active high transmit interrupt. Under this condition when the LM3554 is engaged in a
Flash event, and the TX2 pin is driven high, both LED1 and LED2 are forced into Torch mode or LED shutdown,
depending on the logic state of Configuration Register 2 bit [0]. After a TX2 event, if the ENVM/TX2/GPIO2 pin is
disengaged, and the TX2 Shutdown bit is set to force Torch mode, the LED current will ramp back to the
previous Flash current level. If the TX2 shutdown bit is programmed to force LED shutdown upon a TX2 event
the Flags Register must be read to resume normal LED operation. Table 2, Figure 11 and Figure 12 detail the
functionality of the ENVM/TX2 input.
ENVM/TX2/GPIO2/INT as an Interrupt Output
In GPIO2 mode the ENVM/TX2/GPIO2 pin can be made to reflect the inverse of the LED Thermal Fault flag
(bit[5] in the Flags Register). Configure the LM3554 for this feature by:
set GPIO Register Bit [6] = 1 (NTC External Flag)
set GPIO Register Bit [3] = 1 (GPIO2 mode)
set GPIO Register Bit [4] = 1 (GPIO2 is an output)
set Configuration Register 1 Bit [3] = 1 (NTC mode)
When the voltage at the LEDI/NTC pin falls below VTRIP (1.05V typical), the LED Thermal Fault Flag (bit [5] in the
Flags Register) is set, and the ENVM/TX2/GPIO2/INT pin is forced low. In this mode the interrupt can only be
reset to the open-drain state by reading back the Flags register.
INDICATOR LED/THERMISTOR (LEDI/NTC)
The LEDI/NTC pin serves a dual function, either as an LED indicator driver or as a threshold detector for a
negative temperature coefficient (NTC) thermistor.
Led Indicator Mode (LEDI)
LEDI/NTC is configured as an LED indicator driver by setting Configuration Register 1 bit [3] = (0) and Torch
Brightness Register bits [1:0] = (0, 1), or Flash Brightness Register bits [1:0] = (0, 1). In Indicator mode there are
4 different current levels available (2.3mA, 4.6mA, 6.9mA, 8.2mA). Bits [7:6] of the Torch Brightness Register set
the 4 different indicator current levels. The LEDI current source has a 1V typical headroom voltage.
Thermal Comparator Mode (NTC)
Writing a (1) to Configuration Register 1 bit [3] disables the indicator current source and configures the LEDI/NTC
pin as a detector for an NTC thermistor. In this mode LEDI/NTC becomes the negative input of an internal
comparator with the positive input internally connected to a reference (VTRIP = 1.05V typical). Additionally,
Configuration Register 2 bit [1] determines the action the device takes if the voltage at LEDI/NTC falls below
VTRIP (while the device is in NTC mode). With Configuration register 2 bit [1] = 0, the LM3554 will be forced into
Torch mode when the voltage at LEDI/NTC falls below VTRIP. With Configuration Register 2 bit [1] = 1 the device
will shut down the current sources when VLEDI/NTC falls below VTRIP. When the LM3554 is forced from Flash into
Torch (by VLEDI/NTC falling below VTRIP), normal LED operation (during the same Flash pulse) can only be restarted by reading from the Flags Register (0xD0) and ensuring the voltage at VLEDI/NTC is above VTRIP. When
VLEDI/NTC falls below VTRIP, and the Flags register is cleared, the LM3554 will go through a 250µs deglitch
time before the flash current falls to either torch mode or goes into shutdown.
ALTERNATIVE EXTERNAL TORCH (AET MODE)
Configuration Register 2 bit [2] programs the LM3554 for Alternative External Torch mode. With this bit set to (0)
(default) TX1/TORCH is a transmit interrupt that forces Torch mode only during a Flash event. For example, if
TX1/TORCH goes high during a Flash event then the LEDs will be forced into Torch mode only for the duration
of the timeout counter. At the end of the timeout counter the LEDs will turn off.
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With Configuration Register 2 bit [2] set to (1) the operation of TX1/TORCH becomes dependent on its
occurrence relative to STROBE. In this mode if TX1/TORCH goes high first, then STROBE goes high, the LEDs
are forced into Torch mode with no timeout. In this mode if TX1/TORCH goes high after STROBE has gone high
then the TX1/TORCH pin operates as a normal TX interrupt, and the LEDs will turn off at the end of the timeout
duration. (See LM3554 TIMING DIAGRAMS, Figure 13, and Figure 14.)
INPUT VOLTAGE MONITOR
The LM3554 has an internal comparator that monitors the voltage at IN and can force the LED current into Torch
mode or into shutdown if VIN falls below the programmable VIN Monitor Threshold. Bit 0 in the VIN Monitor
register (0x80) enables or disables this feature. When enabled, Bits 1and 2 program the 4 adjustable thresholds
of 3.1V, 3.2V, 3.3V, and 3.4V. Bit 3 in Configuration Register 2 (0xF0) selects whether an under-voltage event
forces Torch mode or forces the LEDs off. See Figure 24/Table 7 and Figure 26/Table 9 for additional
information.
There is a set 100mV hysteresis for the input voltage monitor. When the input voltage monitor is active, and VIN
falls below the programmed VIN Monitor Threshold, the LEDs will either turn off or their current will get reduced
to the programmed Torch current setting. To reset the LED current to its previous level, two things must occur.
First, VIN must go at least 100mV above the UVLO threshold and secondly, the Flags register must be read back.
LM3554 TIMING DIAGRAMS
I2C Torch
Command
Default State
Flash Brightness Register bit 7 (STR) = 0
Configuration Register 1 bit 7 (TX1/TORCH) = 0
Configuration Register 1 bit 6 (TX2 Polarity) = 1
Configuration Register bit 5 (ENVM/TX2) = 0
Configuration Register 2 bit 2 (AET) = 0
STROBE
I FLASH
I TORCH
I LED
Timeout
Duration
Figure 6. Normal Torch to Flash Operation (Default, Power On or RESET state of LM3554)
TX1/TORCH
STROBE
Default State
(TX event during a STROBE event)
I FLASH
I TORCH
I LED
Timeout
Duration
Figure 7. TX1 Event During a Flash Event (Default State,TX1/TORCH is an Active High TX Input)
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TX1/TORCH
STROBE
Default State
(TX1 event before and after STROBE event)
I TORCH
I LED
Timeout
Duration
Figure 8. TX1 Event Before and After Flash Event (Default State, TX1/TORCH is an Active High TX Input)
I2C Torch
Command
Default State
STROBE goes high and the LEDs turn on into Flash
mode. LEDs will turn off at the end of timeout
duration or when STROBE goes low. Everytime
STROBE goes high the timeout resets.
STROBE
I FLASH
I TORCH
ILED
Timeout
Duration
Start of
Timeout
Counter
Timeout
Counter
Reset
Figure 9. STROBE Input is Level Sensitive (Default State, STR bit = 0)
I2C Torch
Command
STROBE
Flash Brightness Register bit 7 (STR) = 1
STROBE goes high and the LEDs turn on into Flash
mode. LEDs will stay on for the timeout duration even
if STROBE goes low before.
IFLASH
I TORCH
I LED
Timeout
Duration
Figure 10. STROBE Input is Edge Sensitive (STR bit = 1)
24
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I2C Torch
Command
ENVM/TX2
ENVM/TX2 as a transmit interrupt
Configuration Register 1 bit 5 (ENVM/TX2) = 1
(ENVM/TX2 operates as a transmit interrupt)
STROBE
IFLASH
ITORCH
ILED
Timeout
Duration
Figure 11. ENVM/TX2 Pin is Configured as an Active High TX Input
I2C Torch
Command
Configuration Register 1 bit 5 (ENVM/TX2) = 1
Configuration Register 1 bit 6 (ENVM/TX2) = 0
(ENVM/TX2 is configured as an active low transmit interrupt)
ENVM/TX2
STROBE
IFLASH
ITORCH
ILED
Timeout
Duration
Figure 12. ENVM/TX2 Pin is Configured as an Active Low TX Input
TX1/TORCH
Configuration Register 2 bit [2] = 1 (AET)
(TX1/TORCH pin goes high first. When STROBE pin
goes high, LEDs will turn on into Torch. Timeout
counter and flash pulse will not start until TX1/TORCH
goes low)
STROBE
I FLASH
ITORCH
ILED
Timeout
Duration
Figure 13. Alternative External Torch Mode (TX1/TORCH Turns on Before STROBE)
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TX1/TORCH
Configuration Register 2 bit [2] = 1 (AET)
(STROBE goes high before TX1)
STROBE
IFLASH
ITORCH
I LED
Timeout
Duration
Figure 14. Alternative External Torch Mode (STROBE Goes High Before TX1/TORCH, Same as Default
with SEM = 0)
TX1/TORCH
STROBE
Configuration Register 1 bit 7 (TX1/TORCH) = 1
(TX1/TORCH pin is a hardware torch input)
IFLASH
ITORCH
ILED
Timeout
Duration
Figure 15. TX1/TORCH Configured as a Hardware Torch input
FLAGS REGISTER AND FAULT INDICATORS
The Flags Register (0xD0) contains the Interrupt and Fault indicators. Five fault flags are available in the
LM3554. These include a Thermal Shutdown, an LED Failure Flag (LEDF) , a Timeout indicator Flag (TO), a
LED Thermal Flag (NTC), and a VIN Monitor Flag. Additionally, two interrupt flag bits TX interrupt and TX2
interrupt indicate a change of state of the TX1/TORCH pin (TX1 mode) and ENVM/TX2 pin (TX2 mode). Reading
back a "1" indicates the TX lines have changed state since the last read of the Flags Register. A read of the
Flags Register resets these bits.
Thermal Shutdown
When the LM3554’s die temperature reaches +150°C the boost converter shuts down, and the NFET and PFET
turn off. Additionally, all three current sources (LED1, LED2, and LEDI) turn off. When the thermal shutdown
threshold is tripped a (1) gets written to bit [1] of the Flag Register (Thermal Shutdown bit). The LM3554 will start
up again when the die temperature falls to below +135°C.
During heavy load conditions when the internal power dissipation in the device causes thermal shutdown, the
part will turn off and start up again after the die temperature cools. This will result in a pulsed on/off operation.
The OVT bit however will only get written once. To reset the OVT bit pull HWEN low, power down the LM3554,
or read the Flags Register.
LED Fault
The LED Fault flag (bit 2 of the Flags Register) reads back a (1) if the part is active in Flash or Torch mode and
either LED1 or LED2 experience an open or short condition. An LED open condition is signaled if the OVP
threshold is crossed at OUT while the device is in Flash or Torch mode. An LED short condition is signaled if the
voltage at LED1 or LED2 goes below 500mV while the device is in Torch or Flash mode.
26
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There is a delay of 250µs before the LEDF flag is valid on a LED short. This is the time from when VLED falls
below the LED short threshold of 500mV (typical) to when the fault flag is valid. There is a delay of 2µs from
when the LEDF flag is valid on an LED open. This delay is the time between when the OVP threshold is
triggered and when the fault flag is valid. The LEDF flag can only be reset to (0) by pulling HWEN low, removing
power to the LM3554, or reading the Flags Register.
Flash Timeout
The TO flag (bit [0] of the Flags Register) reads back a (1) if the LM3554 is active in Flash mode and the
Timeout period expires before the Flash pulse is terminated. The flash pulse can be terminated before the
Timeout period expires by pulling the STROBE pin low (with STR bit '0'), or by writing a ‘0’ to bit 0 or 1 of the
Torch Brightness Register or the Flash Brightness Register. The TO flag is reset to (0) by pulling HWEN low,
removing power to the LM3554, reading the Flags Register, or when the next Flash pulse is triggered.
LED Thermal Fault
The NTC flag (bit [5] of the Flags Register) reads back a (1) if the LM3554 is active in Flash or Torch mode, the
device is in NTC mode, and the voltage at LEDI/NTC has fallen below VTRIP (1.05V typical). When this has
happened and the LM3554 has been forced into Torch or LED shutdown (depending on the state of
Configuration Register 2 bit [1], the Flags Register must be read in order to place the device back in normal
operation. (See Thermal Comparator Mode (NTC) section for more details.)
Input Voltage Monitor Fault
The VIN Monitor Flag (bit [6] of the Flag Register) reads back a '1' when the Input Voltage Monitor is enabled and
VIN falls below the programmed VIN Monitor threshold. This flag must be read back in order to resume normal
operation after the LED current has been forced to Torch mode or turned off due to a VIN Monitor event.
TX1 and TX2 Interrupt Flags
The TX1 and TX2 interrupt flags (bits [3] and [4]) indicate a TX event on the TX1/TORCH and ENVM/TX2 pins.
Bit 3 will read back a (1) if TX1/TORCH is in TX1 mode and the pin has changed from low to high since the last
read of the Flags Register. Bit 4 will read back a (1) if ENVM/TX2 is in TX2 mode and the pin has had a TX
event since the last read of the Flags Register. A read of the Flags Register automatically resets these bits.
The ENVM/TX2/GPIO2 pin, when configured in TX2 mode, has a TX event that can be either a high-to-low
transition or a low-to-high transition depending on the setting of the TX2 polarity bit (see Configuration Register 1
Bit [6]).
I2C-Compatible Interface
START AND STOP CONDITIONS
The LM3554 is controlled via an I2C-compatible interface. START and STOP conditions classify the beginning
and end of the I2C session. A START condition is defined as SDA transitioning from HIGH to LOW while SCL is
HIGH. A STOP condition is defined as SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master
always generates the START and STOP conditions.
SDA
SCL
S
P
Start Condition
Stop Condition
Figure 16. Start and Stop Sequences
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The I2C bus is considered busy after a START condition and free after a STOP condition. During data
transmission the I2C master can generate repeated START conditions. A START and a repeated START
condition are equivalent function-wise. The data on SDA must be stable during the HIGH period of the clock
signal (SCL). In other words, the state of SDA can only be changed when SCL is LOW. Figure 2 and Figure 17
show the SDA and SCL signal timing for the I2C-Compatible Bus. See the Electrical Characteristics Table for
timing values.
t1
SCL
t5
t4
SDA_IN
t2
SDA_OUT
t3
Figure 17. I2C-Compatible Timing
I2C-COMPATIBLE CHIP ADDRESS
The device address for the LM3554 is 1010011 (53). After the START condition, the I2C master sends the 7-bit
address followed by an eighth bit, read or write (R/W). R/W = 0 indicates a WRITE and R/W = 1 indicates a
READ. The second byte following the device address selects the register address to which the data will be
written. The third byte contains the data for the selected register.
MSB
1
Bit 7
LSB
0
Bit 6
1
Bit 5
0
Bit 4
0
Bit 3
1
Bit 2
1
Bit 1
R/W
Bit 0
2
I C Slave Address (chip address)
Figure 18. 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 (write mode). The LM3554
pulls down SDA during the 9th clock pulse, signifying an acknowledge. An acknowledge is generated after each
byte has been received.
Register Descriptions
Table 1. LM3554 Internal Registers
28
Register Name
Internal Hex Address
Power On or Reset Value
Torch Brightness
0xA0
0x50
Flash Brightness
0xB0
0x68
Flash Duration
0xC0
0x4F
Flag Register
0xD0
0x40
Configuration Register 1
0xE0
0x42
Configuration Register 2
0xF0
0xF0
GPIO Register
0x20
0x80
VIN Monitor Register
0x80
0xF0
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TORCH BRIGHTNESS REGISTER
Bits [2:0] of the Torch Brightness Register, or bits [2:0] of the Flash Brightness Register place the device in
shutdown or control the on/off state of Torch, Flash, the Indicator LED and the Voltage output mode (see
Table 2). Writing to Torch Brightness Register bits [2:0] automatically updates the Flash Brightness Register bits
[2:0]; writing to bits [2:0] of the Flash Brightness Register automatically updates bits [2:0] of the Torch Brightness
Register. Bits [5:3] set the current level in Torch mode (see Table 2). Bits [7:6] set the LED Indicator current level
(see Table 2).
Torch Brightness Register
Register Address 0xA0
MSB
IND1
Bit 7
IND0
Bit 6
TC1
Bit 4
TC2
Bit 5
TC0
Bit 3
LSB
VM
Bit 2
EN1
Bit 1
EN0
Bit 0
Figure 19. Torch Brightness Register Description
Table 2. Torch Brightness Register Bit Settings
Bit 7 (IND1)
Bit 6 (IND0)
Indicator Current Select Bits
00
=
2.3mA
01 = 4.6mA (default state)
10
=
6.9mA
11 = 8.2mA
Bit 5 (TC2)
Bit 4 (TC1)
Bit 3 (TC0)
Torch
Current
Select
000
=
17mA
(34mA
001
=
35.5mA
(71mA
010 = 54mA (108mA total) default
011
=
73mA
(146mA
100
=
90mA
(180mA
101
=
109mA
(218mA
110
=
128mA
(256mA
111 = 147.5mA (295mA total)
Bit 2 (VM)
Bits
total)
total)
state
total)
total)
total)
total)
Bit 1 (EN1)
Bit 0 (EN0)
Enable
Bits
000
=
Shutdown
(default)
001
=
Indicator
Mode
010
=
Torch
Mode
011 = Flash Mode (bits reset at timeout)
100
=
Voltage
Output
Mode
101 = Voltage Output + Indicator Mode
110
=
Voltage
Output
+
Torch
Mode
111 = Voltage Output + Flash Mode (bits [1:0] are
reset at end of timeout)
FLASH BRIGHTNESS REGISTER
Bits [2:0] of the Torch Brightness Register, or bits [2:0] of the Flash Brightness Register place the device in
shutdown or control the on/off state of Torch, Flash, the Indicator LED and the Voltage output mode. Writing to
the Flash Brightness Register bits [2:0] automatically updates the Torch Brightness Register bits [2:0]. Bits [6:3]
set the current level in Flash mode (see Table 3). Bit [7] sets the STROBE Termination select bit (STR) (see
Table 3).
Flash Brightness Register
Register Address 0xB0
MSB
STR
Bit 7
FC3
Bit 6
FC2
Bit 5
FC1
Bit 4
FC0
Bit 3
LSB
VM
Bit 2
EN1
Bit 1
EN0
Bit 0
Figure 20. Flash Brightness Register Description
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Table 3. Flash Brightness Register Bit Settings
Bit 7 (STR)
STROBE Edge or Level
Select
0 = (Level Sensitive) When
STROBE goes high, Flash
current will turn on and
remain on for the duration the
STROBE pin is held high or
when Flash Timeout occurs,
whichever
comes
first.(default)
1 = (Edge Triggered) When
STROBE goes high , Flash
current will turn on and
remain on for the duration of
the Flash Timeout.
Bit 6 (FC3)
Bit 5 (FC2)
Bit 4 (FC1)
Bit 3 (FC0)
Flash
Current
Select
0000
=
35.5mA
(71mA
0001
=
73mA
(146mA
0010
=
109mA
(218mA
0011
=
147.5mA
(295mA
0100
=
182.5mA
(365mA
0101
=
220.5mA
(441mA
0110
=
259mA
(518mA
111
=
298mA
(596mA
1000
=326mA
(652mA
1001
=
364.5mA
(729mA
1010
=
402.5mA
(805mA
1011
=
440.5mA
(881mA
1100
=
480mA
(960mA
1101
=
518.5mA
(1037mA
total)
1110
=
556.5mA
(1113mA
1111 = 595.5mA (1191mA total)
Bit 2 (VM)
Bits
total)
total)
total)
total)
total)
total)
total)
total)
total)
total)
total)
total)
total)
Default
total)
Bit 1 (EN1)
Bit 0 (EN0)
Enable
Bits
000
=
Shutdown
(default)
001
=
Indicator
Mode
010
=
Torch
Mode
011 = Flash Mode (bits reset at timeout)
100
=
Voltage
Output
Mode
101 = Voltage Output + Indicator Mode
110 = Voltage Output + Torch Mode
111 = Voltage Output + Flash Mode (bits [1:0]
are reset at end of timeout)
FLASH DURATION REGISTER
Bits [4:0] of the Flash Duration Register set the Flash Timeout duration. Bits [6:5] set the switch current limit. Bit
[7] defaults as a '1' and is not used (see Table 4).
Flash Duration Register
Register Address 0xC0
MSB
N/A
Bit 7
CL1
Bit 6
CL0
Bit 5
T4
Bit 4
T3
Bit 3
LSB
T2
Bit 2
T1
Bit 1
T0
Bit 0
Figure 21. Flash Duration Register Description
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Table 4. Flash Duration Register Bit Settings
Bit 7 (Not
used)
Reads Back '0'
Bit 6 (CL1)
Bit 5 (CL0)
Current
Limit
Select
Bits
00 = 1A Peak Current Limit
01 = 1.5A Peak Current Limit
t10 = 2A Peak Current
Limi(default)
11 = 2.5A Peak Current Limit
Bit 4 (T4)
Bit 3 (T3)
Bit 2 (T2)
Flash
Timeout
00000
=
00001
=
00010
=
00011
=
00100
=
00101
=
00110
=
00111
=
01000
=
01001
=
01010
=
01011
=
01100
=
01101
=
01110
=
01111
=
512ms
10000
=
10001
=
10010
=
10011
=
10100
=
10101
=
10110
=
10111
=
11000
=
11001
=
11010
=
11011
=
11100
=
11101
=
11110
=
11111 = 1024ms timeout
Bit 1 (T1)
Select
32ms
64ms
96ms
128ms
160ms
192ms
224ms
256ms
288ms
320ms
352ms
384ms
416ms
448ms
480ms
timeout
544ms
576ms
608ms
640ms
672ms
704ms
736ms
768ms
800ms
832ms
864ms
896ms
928ms
960ms
992ms
Bit 0 (T0)
Bits
timeout
timeout
timeout
timeout
timeout
timeout
timeout
timeout
timeout
timeout
timeout
timeout
timeout
timeout
timeout
(default)
timeout
timeout
timeout
timeout
timeout
timeout
timeout
time-out
timeout
timeout
timeout
timeout
timeout
timeout
timeout
FLAGS REGISTER
The Flags Register holds the status of the flag bits indicating LED Failure, Over-Temperature, the Flash Timeout
expiring, VIN Monitor Fault, LED over temperature (NTC), and a TX interrupt. (See Figure 21 and Table 4.)
Flags Register
Register Address 0xD0
MSB
VIN Monitor
Fault
Bit 7
N/A
Bit 6
LED Thermal
Fault
Bit 5
TX2
Interrupt
Bit 4
TX1
Interrupt
Bit 3
LSB
LED
Fault
Bit 2
Thermal
Shutdown
Bit 1
Flash
Timeout
Bit 0
Figure 22. Flags Register Description
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Table 5. Flags Register Bit Settings
Bit 7 (VIN
Monitor Fault
Fault)
Bit 6 (Unused)
Bit 5 (LED
Thermal
Fault)
Bit 4 (TX2
Interrupt)
Bit 3 (TX1
Interrupt )
Bit 2 (Led
Fault)
0=No Fault at
VIN (default)
Not Used
(Reads Back
'1')
0=LEDI/NTC
pin is above
VTRIP (default)
0=ENVM/TX2
has not
changed state
(default)
0=TX1/TORCH
has not changed
state (default)
0 = Proper
LED Operation
(default)
1=LEDI/NTC
has fallen
below
VTRIP(NTC
mode only)
1=ENVM/TX2
has changed
state (TX2
mode only)
1=TX1/TORCH
pin has changed
state (TX1 mode
only)
1 = LED Failed
(Open or Short
1=Input
Voltage
Monitor is
enabled and
VIN has fallen
below the
programmed
threshold
Bit 1 (Thermal
Shutdown)
Bit 0 (Flash
Timeout)
0 = Die
0 = Flash
Temperature
TimeOut did not
below Thermal expire (default)
Shutdown Limit
(default)
1 = Die
Temperature
has crossed
the Thermal
Shutdown
Threshold
1 = Flash
TimeOut
Expired
CONFIGURATION REGISTER 1
Configuration Register 1 holds the light load disable bit, the voltage mode select bit (OV), the external flash
inhibit bit, the control bit for the LEDI/NTC pin, the control bit for ENVM to TX2 mode, the polarity selection bit for
the TX2 input, and the control bit for the TX1/TORCH bit (see Figure 23 and Table 6).
Configuration Register 1
Register Address 0xE0
MSB
LSB
TX1/
TORCH
TX2
Polarity
ENVM/TX2
HYST
LEDI/NTC
Ext Flash
Inhibit
OV
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
LL
Disable
Bit 0
Figure 23. Configuration Register1 Description
Table 6. Configuration Register 1 Bit Settings
Bit 7
(Hardware
Torch Mode
Enable)
Bit 6 (TX2
Polarity)
Bit 5
(ENVM/TX2)
Bit 4 (N/A)
Bit 3
(LEDI/NTC)
Bit 2 (External
Flash Inhibit)
Bit 1 (OV,
Output
Voltage
Select)
Bit 0
(Disable Light
Load )
0=
TX1/TORCH is
a TX1 flash
interrupt input
(default)
0 = ENVM/TX2
pin is an active
low Flash
inhibit
0 = ENVM
Mode The
ENVM/TX2 pin
is a logic input
to enable
Voltage Mode.
A high on
ENVM/TX2 will
force Voltage
Output Mode
(default)
Reads Back '0'
0 = LEDI/NTC
pin in Indicator
mode (default)
0 = STROBE
Input Enabled
(default)
0 = Voltage
Mode output
voltage is 4.5V
0 = Light load
comparator is
enabled. The
LM3554 will go
into PFM mode
at light load
(default).
1=
TX1/TORCH
pin is a
hardware
TORCH enable
1 = ENVM/TX2 1 = TX2 Mode
pin is an active The ENVM/TX2
high Flash
is a Power
inhibit (default)
Amplifier
Synchronization
input. A high on
ENVM/TX2 will
force the
LM3554 from
Flash to Torch
mode.
1 = LEDI/NTC
pin in Thermal
Comparator
Mode. Indicator
current is
disabled.
1 = STROBE
Input Disabled
1 = Voltage
Mode output
voltage is 5V
(default)
1 = Light load
comparator is
disabled. The
LM3554 will not
go into PFM
mode at light
load.
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CONFIGURATION REGISTER 2
Configuration Register 2 contains the bits to select if TX2, NTC, and the VIN monitor force Torch mode or force
the Flash LEDs into shutdown. Additionally, bit [2] (AET bit) selects the Alternate External Torch mode (see
Figure 24 and Table 7).
Configuration Register 2
Register Address 0xF0
MSB
N/A
N/A
N/A
N/A
Bit 7
Bit 6
Bit 5
Bit 4
VIN Monitor
Mode
Bit 3
LSB
AET
Mode
Bit 2
TX2
Shutdown
NTC
Shutdown
Bit 1
Bit 0
Figure 24. Configuration Register 2 Description
Table 7. Configuration Register 2 Bit Settings
Bit 7 (Not
used)
Bit 6 (Not
used)
Bit 5 (Not
used)
Bit 4 (Not
used)
Bit 3 (VIN
Monitor
Shutdown)
Bit 2 (AET
mode)
Bit 1
(NTC
Shutdown)
Bit 0
(TX2
Shutdown)
Reads Back '1'
Reads Back '1'
Reads Back '1'
Reads Back '1'
0 = If IN drops
below the
programmed
threshold and
the VIN Monitor
feature is
enabled, the
LED's are
forced into
Torch mode
(default)
0 = Normal
operation for
TX1/TORCH
high before
STROBE (TX1
mode only)
default
0 = LEDI/NTC
pin going below
VTRIP forces the
LEDs into
Torch mode
(NTC mode
only) default
0 = TX2 event
forces the
LEDs into
Torch mode
(TX2 mode
only) default
1 = If IN drops
below the
programmed
threshold and
the VIN Monitor
feature is
enabled, the
LED's turn off
1 = Alternative
External Torch
operation.
TX1/TORCH
high before
STROBE
forces Torch
mode with no
timeout (TX1
mode only)
1 = LEDI/NTC
1 = TX2 event
pin going below
forces the
VTRIP forces the
LEDs into
LEDs into
shutdown (TX2
shutdown (NTC
mode only)
mode only)
GPIO REGISTER
The GPIO register contains the control bits which change the state of the TX1/TORCH/GPIO1 pin and the
ENVM/TX2/GPIO2 pin to general purpose I/O’s (GPIO’s). Additionally, bit[6] of this register configures the
ENVM/TX2/GPIO2 as a hardware interrupt output reflecting the NTC flag bit in the Flags Register. Figure 25 and
Table 8 describe the bit description and functionality of the GPIO register.
GPIO Register
Register Address 0x20
MSB
Not
Used
Bit 7
NTC
External
Flag
Bit 6
Data
Data
Direction
Bit 5
Bit 4
ENVM/
TX2/GPIO2
Bit 3
LSB
Data
Bit 2
Data
Direction
Bit 1
TX1/TORCH/
GPIO1
Bit 0
Figure 25. GPIO Register Description
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Table 8. GPIO Register Bit Settings
Bit 7 (Not
Used)
Bit 6 (NTC
External Flag)
Reads Back '1'
0 = NTC
External Flag
mode is
disabled
(default)
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(ENVM/TX2/GP (ENVM/TX2/GP (ENVM/TX2/GP (TX1/TORCH/G (TX1/TORCH/G (TX1/TORCH/G
IO2 data)
IO2 data
IO2 Control)
PIO1 data)
PIO1 data
PIO1 Control)
direction)
direction)
This bit is the
0=
0=
read or write
ENVM/TX2/GPI ENVM/TX2/GPI
data for the
O2 is a GPIO
O2 is
ENVM/TX2/GPI Input (default)
configured
O2 pin in GPIO
according to
mode (default
the
is 0)
Configuration
Register bit 5
(default)
1 = When
ENVM/TX2/GPI
O2 is
configured as a
GPIO output
the
ENVM/TX2/GPI
O2 pin will pull
low when the
LED Thermal
Fault Flag is set
This bit is the
read or write
data for the
TX1/TORCH/G
PIO1 pin in
GPIO mode
(default is 0)
1=
1=
ENVM/TX2/GPI ENVM/TX2/GPI
O2 is a GPIO
O2 is
Output
configured as a
GPIO
0=
TX1/TORCH/G
PIO1 is a GPIO
input (default)
0=
TX1/TORCH/G
PIO1 pin is
configured as
an active low
reset input
(default)
1=
1=
TX!/TORCH/GP TX1/TORCH/G
IO1 is an
PIO1 pin is
output
configured as a
GPIO
VIN MONITOR REGISTER
The VIN Monitor Register controls the on/off state of the VIN Monitor comparator as well as selects the 4
programmable thresholds. Figure 26 and Table 9 describe the bit settings of the VIN Monitor feature.
VIN Monitor Register
Register Address 0x80
MSB
LSB
N/A
N/A
N/A
N/A
N/A
VIN
Threshold
VIN
Threshold
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
VIN
Monitor
Enable
Bit 0
Figure 26. VIN Monitor Register Description
Table 9. VIN Monitor Register Bit Settings
Bit 7 (Not
used)
Bit 6 (Not
used)
Bit 5 (Not
used)
Bit 4 (Not
used)
Bit 3 (Not used)
Reads Back '1'
Reads Back '1'
Reads Back '1'
Reads Back '1'
Reads Back '0'
Bit 2 (VIN
Threshold)
Bit 1 (VIN
Threshold)
00 = 3.1V threshold (VIN falling)
Default
01=3.2V threshold (VIN falling)
10 = 3.3V threshold (VIN falling)
11 = 3.4V threshold (VIN falling)
Bit 0 (VIN
Monitor Enable)
0 = VIN
Monitoring
Comparator is
disabled
(default)
1 = VIN
Monitoring
Comparator is
enabled.
Applications Information
OUTPUT CAPACITOR SELECTION
The LM3554 is designed to operate with a at least a 4.7µF ceramic output capacitor in LED mode and a 10µF
output capacitor in Voltage Output Mode. When the boost converter is running the output capacitor supplies the
load current during the boost converters on-time. When the NMOS switch turns off the inductor energy is
discharged through the internal PMOS switch 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.
34
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For proper LED operation the output capacitor must be at least a 4.7µF ceramic (10µF in Voltage Output Mode).
Larger capacitors such as 10µF or 22µF can be used if lower output voltage ripple is desired. To estimate the
output voltage ripple considering the ripple due to capacitor discharge (ΔVQ) and the ripple due to the capacitors
ESR (ΔVESR) use the following equations:
For continuous conduction mode, the output voltage ripple due to the capacitor discharge is:
'VQ =
ILED x (VOUT - VIN)
fSW x VOUT x COUT
(7)
The output voltage ripple due to the output capacitors ESR is found by:
'VESR = R ESR x §
©
where
'IL =
I LED x VOUT·
VIN
¹
+ 'I L
VIN x (VOUT - VIN )
2 x f SW x L x VOUT
(8)
In ceramic capacitors the ESR is very low so assume that 80% of the output voltage ripple is due to capacitor
discharge and 20% from ESR. Table 10 lists different manufacturers for various output capacitors and their case
sizes suitable for use with the LM3554.
INPUT CAPACITOR SELECTION
Choosing the correct size and type of input capacitor helps minimize the voltage ripple caused by the switching
of the LM3554’s boost converter and reduces noise on the devices input terminal that can feed through and
disrupt internal analog signals. In the Typical Application Circuit a 4.7µF ceramic input capacitor works well. It is
important to place the input capacitor as close as possible to the LM3554’s input (IN) terminals. This reduces the
series resistance and inductance that can inject noise into the device due to the input switching currents.
Table 10 lists various input capacitors that or recommended for use with the LM3554.
Table 10. Recommended Input/Output Capacitors (X5R Dielectric)
Manufacturer
Part Number
Value
Case Size
Voltage Rating
TDK Corporation
C1608JB0J475K
4.7µF
0603(1.6mm×0.8mm×0.8mm)
6.3V
TDK Corporation
C1608JB0J106M
10µF
0603(1.6mm×0.8mm×0.8mm)
6.3V
TDK Corporation
C2012JB1C475K
4.7µF
0805(2mm×1.25mm×1.25mm)
16V
TDK Corporation
C2012JB1A106M
10µF
0805(2mm×1.25mm×1.25mm)
10V
TDK Corporation
C2012JB0J226M
22µF
0805(2mm×1.25mm×1.25mm)
6.3V
Murata
GRM188R60J475KE19
4.7µF
0603(1.6mm×0.8mm×0.8mm)
6.3V
Murata
GRM21BR61C475KA88
4.7µF
0805(2mm×1.25mm×1.25mm)
16V
Murata
GRM21BR61A106KE19
10µF
0805(2mm×1.25mm×1.25mm)
10V
Murata
GRM21BR60J226ME39L
22µF
0805(2mm×1.25mm×1.25mm)
6.3V
INDUCTOR SELECTION
The LM3554 is designed to use a 2.2µH inductor. Table 11 lists various inductors and their manufacturers that
can work well with the LM3554. When the device is boosting (VOUT > VIN) the inductor will typically be the biggest
area of efficiency loss in the circuit. Therefore, choosing an inductor with the lowest possible series resistance is
important. Additionally, the saturation rating of the inductor should be greater than the maximum operating peak
current of the LM3554. This prevents excess efficiency loss that can occur with inductors that operate in
saturation and prevents over heating of the inductor and possible damage. For proper inductor operation and
circuit performance ensure that the inductor saturation and the peak current limit setting of the LM3554 is greater
than IPEAK can be calculated by:
I LOAD VOUT
VIN x (VOUT - VIN)
IPEAK =
K
x
VIN
+ 'IL where 'IL =
2 x f SW x L x VOUT
(9)
ƒSW = 2MHz; η can be found in the Typical Performance Characteristics plots.
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Table 11. Recommended Inductors
Manufacturer
L
Part Number
Dimensions (L×W×H)
ISAT
TOKO
2.2µH
FDSE0312-2R2M
3mm×3mm×1.2mm
2A
TDK
2.2µH
VLS252012T-2R2M1R3
2mm×2.5mm×1.2mm
1.5A
Coilcraft
2.2µH
LPS4018-222ML
3.9mmx3.9mmx1.7mm
2.3A
NTC THERMISTOR SELECTION
NTC thermistors have a temperature to resistance relationship of:
1
1 ·
E§
T °C + 273 298
©
¹
R(T) = R25°C x e
(10)
where β is given in the thermistor datasheet and R25C is the thermistors value at +25°C. R3 in Figure 28 is
chosen so that it is equal to:
R3 =
RT( TRIP) (VBIAS - VTRIP )
VTRIP
(11)
where R(T)TRIP is the thermistors value at the temperature trip point, VBIAS is shown in Figure 28, and VTRIP =
1.05V (typical). Choosing R3 here gives a more linear response around the temperature trip voltage. For
example, with VBIAS = 2.5V, a thermistor whose nominal value at +25°C is 100kΩ and a β = 4500K, the trip point
is chosen to be +93°C. The value of R(T) at 93°C is:
E
R3 is then:
º
»
¼
R(T) = 100 k : x e
º
1
- 1 »
93 + 273 298 ¼
= 6.047 k :
6.047 k: x (2.5 V - 1V)
= 9 .071 k:
1V
(12)
Figure 27 shows the linearity of the thermistor resistive divider of the previous example.
1.5
VBIAS = 2.5V,
RTHERMISTOR = 100 k:
@ +25°C, B = 4500,
R3 = 9 k:
1.4
1.3
V LEDI/NTC (V)
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
70
75
80
85
90
95
100 105 110
TEMPERATURE (°C)
Figure 27. Thermistor Resistive Divider Response vs Temperature
Another useful equation for the thermistor resistive divider is developed by combining the equations for R3, and
R(T) and solving for temperature. This gives the following relationship.
T( °C) =
E x 298 °C
VTRIP x R3
ª
º E
298°C x LN
«(VBIAS - VTRIP ) x R25 °C» +
¬
¼
- 273°C
(13)
Using a spreadsheet such as Excel, different curves for the temperature trip point T(°C) can be created vs R3,
Beta, or VBIAS in order to help better choose the thermal components for practical values of thermistors, series
resistors (R3), or reference voltages VBIAS.
36
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Programming bit [3] of the Configuration register with a (1) selects Thermal Comparator mode making the
LEDI/NTC pin a comparator input for flash LED thermal sensing. Figure 28 shows the internal block diagram of
the thermal sensing circuit which is OR’d with both the TX1 and ENVM/TX2 (TX2 mode) to force the LM3554
from Flash to Torch mode. This is intended to prevent LED overheating during flash pulses.
Internal to
LM3554
TX2
VIN Monitor
TX1/TORCH
Force Torch or
LED Shutdown (VIN Monitor, TX2 or
NTC only)
VBIAS
1.05V
R3
LEDI/
NTC
+
R(T)
0.1 PF
Figure 28. Thermistor Voltage Divider and Sensing Circuit
NTC THERMISTOR PLACEMENT
The termination of the thermistor must be done directly to the cathode of the Flash LED in order to adequately
couple the heat from the LED into the thermistor. Consequentally, the noisy environment generated from the
switching of the LM3554's boost converter can introduce noise from GND into the thermistor sensing input. To
filter out this noise it is necessary to place a 0.1µF or larger ceramic capacitor close to the LEDI/NTC pin. The
filter capacitor's return must also connect with a low-impedance trace, as close as possible to the PGND pin of
the LM3554.
Layout Recommendations
The high frequency and large switching currents of the LM3554 make the choice of layout important. The
following steps should be used as a reference to ensure the device is stable and maintains proper voltage and
current regulation across its intended operating voltage and current range.
1. Place CIN on the top layer (same layer as the LM3554) 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 on both the IN and
GND terminals will reduce the inductive voltage spikes that occur during switching and which can corrupt the
VIN line.
2. Place COUT on the top layer (same layer as the LM3554) and as close as possible to the OUT and GND
terminal. The returns for both CIN and COUT should come together at one point, and 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 line 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 TX1/TORCH/GPIO1, ENVM/TX2/GPIO2, HWEN, LEDI/NTC (NTC
mode), SDA, and SCL. A good approach is to insert an inner layer GND plane underneath the SW node and
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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 LM3554. If possible, route the LED returns
with a dedicated path so as to keep the high amplitude LED currents out the GND plane. For Flash LEDs
that are routed relatively far away from the LM3554, 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.
6. The NTC Thermistor is intended to have its return path connected to the LED's cathode. This allows the
thermistor resistive divider voltage (VNTC) to trip the comparators threshold as VNTC is falling. Additionally, the
thermistor-to-LED cathode junction can have low thermal resistivity since both the LED and the thermistor
are electrically connected at GND. The drawback is that the thermistor's return will see the switching currents
from the LM3554's boost converter. Because of this, it is necessary to have a filter capacitor at the NTC pin
which terminates close to the GND of the LM3554 and which can conduct the switched currents to GND.
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PACKAGE OPTION ADDENDUM
www.ti.com
17-Nov-2012
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)
LM3554TME/NOPB
ACTIVE
DSBGA
YFQ
16
250
Green (RoHS
& no Sb/Br)
SNAGCU
Level-1-260C-UNLIM
LM3554TMX/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
17-Nov-2012
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
LM3554TME/NOPB
DSBGA
YFQ
16
250
178.0
8.4
LM3554TMX/NOPB
DSBGA
YFQ
16
3000
178.0
8.4
Pack Materials-Page 1
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
1.85
2.01
0.76
4.0
8.0
Q1
1.85
2.01
0.76
4.0
8.0
Q1
PACKAGE MATERIALS INFORMATION
www.ti.com
17-Nov-2012
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM3554TME/NOPB
DSBGA
YFQ
LM3554TMX/NOPB
DSBGA
YFQ
16
250
203.0
190.0
41.0
16
3000
206.0
191.0
90.0
Pack Materials-Page 2
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