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LM3554
SNVS549C – JUNE 2009 – REVISED FEBRUARY 2016
LM3554 Synchronous Boost Converter With 1.2-A Dual High-Side LED Drivers and I2CCompatible Interface
1 Features
3 Description
•
•
The LM3554 is a 2-MHz fixed-frequency, currentmode synchronous boost converter. The device is
designed to operate as a dual 600-mA (1.2 A total)
constant-current driver for high-current white LEDs, or
as a regulated 4.5-V or 5-V voltage source.
1
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Input Voltage: 2.5 V to 5.5 V
Programmable 4.5-V or 5-V Constant Output
Voltage
Dual High-Side Current Sources
Grounded Cathode Allowing for Better Heat
Sinking and LED Routing
> 90% Efficiency
Ultra-Small Solution Size: < 23 mm2
Four Operating Modes: Torch, Flash, LED
Indicator, and Voltage Output
Accurate and Programmable LED Current from
37.5 mA to 1.2 A
Hardware Flash and Torch Enable
LED Thermal Sensing and Current Scaleback
Software Selectable Input Voltage Monitor
Programmable Flash Timeout
Dual Synchronization Inputs for RF PowerAmplifier Pulse Events
Open and Short LED Detection
Active High Hardware Enable for Protection
Against System Faults
400-kHz I2C-Compatible Interface
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 overvoltage 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.
Device Information(1)
PART NUMBER
2 Applications
•
•
•
LM3554
Camera Phone LED Flash Controller
Class D Audio Amplifier Power
LED Current Source Biasing
PACKAGE
DSBGA (16)
BODY SIZE (MAX)
1.685 mm × 1.685
mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Application Circuit
2.2 µH
4.5-V or 5-V DC Power Rail
SW
2.5 V ± 5.5 V
IN
OUT
4.7 µF
HWEN
SCL
SDA
LM3554
4.7 µF
VBIAS
LED1
LED2
STROBE
TX1/TORCH/
LEDI/NTC
GPIO1
ENVM/TX2
/GPIO GND
D2
Indicator
LED
Flash
LEDs
D1
RBIAS
0.1 µF
2 NŸ
Thermistor
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM3554
SNVS549C – JUNE 2009 – REVISED FEBRUARY 2016
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
4
4
4
4
5
6
7
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Timing Requirements ................................................
Typical Characteristics ..............................................
Detailed Description ............................................ 12
7.1
7.2
7.3
7.4
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
12
13
13
21
7.5 Programming........................................................... 22
7.6 Register Maps ......................................................... 23
8
Application and Implementation ........................ 29
8.1 Application Information............................................ 29
8.2 Typical Application ................................................. 29
9 Power Supply Recommendations...................... 39
10 Layout................................................................... 40
10.1 Layout Guidelines ................................................. 40
10.2 Layout Example .................................................... 40
11 Device and Documentation Support ................. 41
11.1
11.2
11.3
11.4
11.5
11.6
Device Support ....................................................
Documentation Support ........................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
41
41
41
41
41
41
12 Mechanical, Packaging, and Orderable
Information ........................................................... 41
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision B (May 2013) to Revision C
•
Added Device Information and Pin Configuration and Functions sections, ESD Ratings and Thermal Information
tables, Feature Description, Device Functional Modes, Application and Implementation, Power Supply
Recommendations, Layout, Device and Documentation Support, and Mechanical, Packaging, and Orderable
Information sections................................................................................................................................................................ 1
Changes from Revision A (May 2013) to Revision B
•
2
Page
Page
Changed layout of National Data Sheet to TI format ........................................................................................................... 40
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SNVS549C – JUNE 2009 – REVISED FEBRUARY 2016
5 Pin Configuration and Functions
YFQ Package
16-Pin DSBGA
Top View
A1
A2
A3
A4
B1
B2
B3
B4
C1
C2
C3
C4
D1
D2
D3
D4
Pin Descriptions
PIN
TYPE
DESCRIPTION
LED1
Power
High-side current source output for flash LED.
OUT
Power
Step-up DC-DC converter output.
A3, B3
SW
Power
Drain connection for internal NMOS and synchronous PMOS switches.
A4, B4
GND
Ground
Ground
B1
LED2
Power
High-side current source output for flash LED.
C1
LEDI/NTC
Input/Output
Configurable as a high-side current source output for indicator LED or
threshold detector for LED temperature sensing.
C2
TX1/TORCH/GPIO1
Input/Output
Configurable as a RF power amplifier synchronization control input (TX1), a
hardware torch enable (TORCH), or a programmable general-purpose logic
input/output (GPIO1).
C3
STROBE
Input
Active high hardware flash enable. Drive STROBE high to turn on flash
pulse.
C4
IN
Power
Input voltage connection. Connect IN to the input supply, and bypass to
GND with a minimum 4.7-µF ceramic capacitor.
D1
ENVM/TX2/GPIO2/INT
Input/Output
Configurable as an active high voltage mode enable (ENVM), dual polarity
power amplifier synchronization input (TX2), or programmable general
purpose logic input/output (GPIO2).
D2
SDA
Input/Output
Serial data input output
D3
SCL
Input
Serial clock input
D4
HWEN
Input
Active low hardware reset
NUMBER
NAME
A1
A2, B2
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1) (2) (3)
VIN, VSW, VOUT
VSCL, VSDA, VHWEN, VSTROBE, VTX1/TORCH, VENVM/TX2, VLED1, VLED2, VLEDI/NTC
MIN
MAX
UNIT
–0.3
6
V
0.3 V to (VIN + 0.3 V)
w/ 6 V max
Continuous power dissipation (4)
Internally limit
Junction temperature, TJ-MAX
Storage temperature, Tstg
(1)
(2)
(3)
(4)
(5)
150
°C
150
°C
See (5)
Maximum lead temperature (soldering)
–65
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltages are with respect to the potential at the GND pin.
If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=150°C (typical) and
disengages at TJ=135°C (typical).
For detailed soldering specifications and information, refer to AN1112 DSBGA Wafer Level Chip-Scale Package (SNVA009).
6.2 ESD Ratings
V(ESD)
(1)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001
VALUE
UNIT
±2000
V
(1)
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted) (1)
MIN
NOM
MAX
UNIT
Input voltage, VIN
2.5
5.5
V
Junction temperature, TJ
–30
125
°C
Ambient temperature, TA (2)
–30
85
°C
(1)
(2)
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 (RθJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX).
6.4 Thermal Information
LM3554
THERMAL METRIC (1)
YFQ (DSBGA)
UNIT
16 PINS
RθJA
Junction-to-ambient thermal resistance
75.8
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
0.5
°C/W
RθJB
Junction-to-board thermal resistance
16.5
°C/W
ψJT
Junction-to-top characterization parameter
0.3
°C/W
ψJB
Junction-to-board characterization parameter
16.4
°C/W
(1)
4
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
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6.5 Electrical Characteristics
Unless otherwise specified, typical limits are for TA = 25°C, minimum and maximum limits in apply over the full operating
ambient temperature range (–30°C ≤ TA ≤ +85°C), VIN = 3.6 V, and VHWEN = VIN. (1) (2)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
CURRENT SOURCE SPECIFICATIONS
Current source
accuracy
ILED
600-mA flash LED setting,
VOUT = VIN
17-mA torch current setting
VHR = 500 mV
VHR
Current source
regulation voltage
(VOUT – VLED)
600-mA setting, VOUT = 3.75 V
IMATCH
LED Current
Matching
600-mA setting, VLED = 3.2 V
ILED1 and ILED2
1128
1200
1284
ILED1 or ILED2
541
600
657
ILED1 and ILED2
30.4
33.8
37.2
300
mA
mV
0.35%
STEP-UP DC-DC CONVERTER
VREG
Output voltage
accuracy
2.7 V ≤ VIN ≤ 4.2 V, IOUT = 0 mA
VENVM = VIN, OV bit = 0
4.8
5
5.2
Output overvoltage
protection trip
point (3)
On threshold, 2.7 V ≤ VIN ≤ 5.5 V
5.4
5.6
5.7
VOVP
RPMOS
RNMOS
5.3
PMOS switch onresistance
IPMOS = 1 A
150
mΩ
NMOS switch onresistance
INMOS = 1 A
150
mΩ
Switch current
limit (4)
IOUT_SC
Output short-circuit
current limit
Indicator current
CL bits = 00
0.711
1.05
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 < 2.3 V
LEDI/NTC bit = 0
IND1, IND0 bits = 00
2.3
IND1, IND0 bits = 01
4.6
IND1, IND0 bits = 10
6.9
IND1, IND0 bits = 11
8.2
Comparator trip
threshold
LEDI/NTC bit = 1, 2.7 V ≤ VIN ≤ 5.5 V
ƒSW
Switching frequency
2.7 V ≤ VIN ≤ 5.5 V
IQ
Quiescent supply
current
Device not switching
630
ISHDN
Shutdown supply
current
2.7 V ≤ VIN ≤ 5.5 V
3.5
tTX
Flash-to-torch LED
current settling time
TX_ Low to High, ILED1 + ILED2 = 1.2 A to 180 mA
20
(3)
(4)
1.373
550
VTRIP
(1)
(2)
V
Off threshold
ICL
ILED/NTC
V
A
mA
mA
0.947
1.052
1.157
V
1.75
2
2.23
MHz
µA
6.6
µA
µs
All voltages are with respect to the potential at the GND pin.
Minimum (MIN) and maximum (MAX) limits are ensured by design, test, or statistical analysis. Typical (TYP) numbers are not ensured,
but do represent the most likely norm. Unless otherwise specified, conditions for typical specifications are: VIN = 3.6 V and TA = 25°C.
The typical curve for overvoltage 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 Electrical
Characteristics 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).
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 Electrical Characteristics 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 20 ns × VIN / L.
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Electrical Characteristics (continued)
Unless otherwise specified, typical limits are for TA = 25°C, minimum and maximum limits in apply over the full operating
ambient temperature range (–30°C ≤ TA ≤ +85°C), VIN = 3.6 V, and VHWEN = VIN. (1)(2)
PARAMETER
TEST CONDITIONS
VIN monitor trip
threshold
VIN_TH
VIN falling, VIN monitor register = 0x01
(enabled with VIN_TH = 3.1 V)
MIN
TYP
MAX
UNIT
2.95
3.09
3.23
V
0.4
V
TX1/TORCH/GPIO1, STROBE, HWEN, ENVM/TX2/GPIO2 VOLTAGE
VIL
Input logic low
2.7 V ≤ VIN ≤ 5.5 V
0
VIH
Input logic high
2.7 V ≤ VIN ≤ 5.5 V
1.2
VOL
Output logic low
ILOAD = 3 mA, 2.7 V ≤ VIN ≤ 5.5 V
RTX1/TORC
Internal pulldown
resistance at
TX1/TORCH
300
kΩ
Internal pulldown
resistance at
STROBE
300
kΩ
H
RSTROBE
VIN
V
400
mV
I2C-COMPATIBLE VOLTAGE SPECIFICATIONS (SCL, SDA)
VIL
Input logic low
2.7 V ≤ VIN ≤ 5.5 V
0
0.4
V
VIH
Input logic high
2.7 V ≤ VIN ≤ 5.5 V
1.22
VIN
V
VOL
Output logic low
(SCL)
ILOAD = 3 mA, 2.7 V ≤ VIN ≤ 5.5 V
400
mV
6.6 Timing Requirements
See Figure 1.
MIN
1 / t1
SCL clock frequency
t2
Data in setup time to SCL high
t3
Data out stable after SCL low
t4
t5
NOM
MAX
400
UNIT
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 1. I2C Timing
6
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6.7 Typical Characteristics
VIN = 3.6 V, LEDs are Lumiled PWF-4, COUT = 10 µF, CIN = 4.7 µF, L = FDSE0312-2R2 (2.2 µH, RL = 0.15 Ω), TA = 25°C,
unless otherwise specified.
VOUT = 5 V
Voltage-Output Mode
VOUT = 5 V
Figure 2. VOUT vs IOUT
Voltage-Output Mode
Figure 3. VOUT vs VIN
VIN = 3.6 V
VLED1, VLED2 = 3.2 V
TA = –40°C to +85°C
Current Matching = Abs Value ((ILED1–ILED2)÷(ILED1+ILED2))×100
VLED1, VLED2 = 3.2 V
75-mA Setting
TA = 25°C
Figure 5. Torch Current vs VIN
Figure 4. Torch Current Matching vs Code
VLED1, VLED2 = 3.2 V
75-mA Setting
TA = 85°C
VLED1, VLED2 = 3.2 V
Figure 6. Torch Current vs VIN
75-mA Setting
TA = –40°C
Figure 7. Torch Current vs VIN
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Typical Characteristics (continued)
VIN = 3.6 V, LEDs are Lumiled PWF-4, COUT = 10 µF, CIN = 4.7 µF, L = FDSE0312-2R2 (2.2 µH, RL = 0.15 Ω), TA = 25°C,
unless otherwise specified.
VIN = 3.6 V
VLED1, VLED2 = 3.2 V
TA = –40°C To +85°C
Current Matching = Abs Value ((ILED1–ILED2)÷(ILED1+ILED2))×100
VLED1, VLED2 = 3.2 V
Figure 8. Flash Current Matching vs Code
VLED1, VLED2 = 3.2 V
600-mA Setting
TA = 85°C
600-mA Setting
TA = 25°C
Figure 9. Flash Current vs VIN
VLED1, VLED2 = 3.2 V
Figure 10. Flash Current vs VIN
600-mA Setting
TA = –40°C
Figure 11. Flash Current vs VIN
VHWEN = 0 V
Figure 12. Switching Frequency vs VIN
8
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Figure 13. Shutdown Current vs VIN
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Typical Characteristics (continued)
VIN = 3.6 V, LEDs are Lumiled PWF-4, COUT = 10 µF, CIN = 4.7 µF, L = FDSE0312-2R2 (2.2 µH, RL = 0.15 Ω), TA = 25°C,
unless otherwise specified.
VLED = 1.5 V
(1)
VOUT = 5 V
IOUT = 400 mA
Figure 14. Active (Non-Switching) Supply Current vs VIN
Figure 15. Active (Switching) Supply Current vs VIN
Figure 16. Closed Loop Current Limit vs VIN
(Flash Duration Register Bits [6:5] = 00) (1))
Figure 17. Closed Loop Current Limit vs VIN
(Flash Duration Register Bits [6:5] = 01) (1) )
Figure 18. Closed Loop Current Limit vs VIN
(Flash Duration Register Bits [6:5] = 10) (1))
Figure 19. Closed Loop Current Limit vs VIN
(Flash Duration Register Bits [6:5] = 11) (1))
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 Electrical Characteristics 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 20 ns × VIN / L.
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Typical Characteristics (continued)
VIN = 3.6 V, LEDs are Lumiled PWF-4, COUT = 10 µF, CIN = 4.7 µF, L = FDSE0312-2R2 (2.2 µH, RL = 0.15 Ω), TA = 25°C,
unless otherwise specified.
Figure 21. OVP Thresholds vs VIN (1)
Figure 20. VIN Monitor Thresholds vs Temperature
VLEDI = 2 V
Figure 23. Indicator Current vs VIN
(Torch Brightness Register Bits[7:6] = 00)
Figure 22. Short Circuit Current Limit vs VIN
VLEDI = 2 V
VLEDI = 2 V
Figure 24. Indicator Current vs VIN
(Torch Brightness Register Bits[7:6] = 01)
(1)
10
Figure 25. Indicator Current vs VIN
(Torch Brightness Register Bits[7:6] = 10)
The typical curve for overvoltage 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 Electrical
Characteristics 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 Characteristics (continued)
VIN = 3.6 V, LEDs are Lumiled PWF-4, COUT = 10 µF, CIN = 4.7 µF, L = FDSE0312-2R2 (2.2 µH, RL = 0.15 Ω), TA = 25°C,
unless otherwise specified.
VLEDI = 2 V
Figure 26. Indicator Current vs VIN
(Torch Brightness Register Bits[7:6] = 11)
Figure 27. NTC Comparator Trip Threshold vs VIN
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7 Detailed Description
7.1 Overview
The LM3554 is a high-power white-LED flash driver capable of delivering up to 1.2-A of LED current into a single
LED, or up to 600 mA into two parallel LEDs. The device incorporates a 2-MHz constant frequency,
synchronous, current mode PWM boost converter, and two high-side current sources to regulate the LED current
over the 2.5-V to 5.5-V 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 – 150 mV, the PWM converter switches and maintains at least 300 mV (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 device goes into switching mode one time. The LM3554 remains in switching mode
until the device is shut down and re-enabled. This is true even if VIN rises back above VLED + 300 mV during the
current flash or torch cycle. This prevents the LED current from oscillating when VIN is operating close to VOUT.
In voltage-output mode the LM3554 operates as a voltage output boost converter with selectable output voltages
of 4.5 V and 5 V. In this mode the LM3554 is able to deliver up to typically 5 W 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 four 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.
The device is controlled via an I2C-compatible interface. This includes switchover 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, overtemperature
condition, LED failure (open or short), LED thermal failure, and an input voltage fault.
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7.2 Functional Block Diagram
SW
Over Voltage
Comparator
+
-
IN
2 MHz
Oscillator
VREF
150 m:
VREF
OUT
ILED1
ILED2
PWM
Control
ILEDI
150 mΩ
LEDI/
NTC
Error
Amplifier
+
-
ISET
LED1
Reference
Mode
Select
LED2
VREF
Thermal
Shutdown
+150oC
+
+
-
Current
Sense/Current
Limit
VTRIP
Feedback
Mode
Select
Max
VLED
Slope
Compensation
SDA
Control
Logic/
Soft-Start
I2C
Interface
SCL
HWEN
TX1/TORCH/
GPIO1
STROBE
ENVM/TX2/
GPIO2
GND
7.3 Feature Description
7.3.1 Start-Up
The device is turned on 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 start-up, when VOUT is less than VIN the internal synchronous PFET turns on as a current source and delivers
typically 350 mA to the output capacitor. During this time all current sources (LED1, LED2, and LEDI) are off.
When the voltage across the output capacitor reaches 2.2 V, the current sources can turn on. At turnon 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 turnon and limits inrush current from the VIN supply.
7.3.2 Overvoltage Protection
The output voltage is limited to typically 5.6 V (5.7 V maximum). In situations such as the current source open,
the LM3554 raises the output voltage in order to keep the LED current at its target value. When VOUT reaches 5.6
V the overvoltage comparator trips and turns off both the internal NFET and PFET. When VOUT falls below 5.4 V
(typical), the LM3554 begins switching again.
7.3.3 Current Limit
The LM3554 features four selectable current limits: 1 A, 1.5 A, 2 A, and 2.5 A. These are selectable through the
I2C-compatible interface via bits 5 (CL0) and 6 (CL1) of the Flash Duration Register. When the current limit is
reached, the LM3554 device stops switching for the remainder of the switching cycle.
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Feature Description (continued)
Because the current limit is sensed in the NMOS switch there is no mechanism to limit the current when the
device operates in pass mode. In 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 2.5 A. In boost mode or pass mode if
VOUT falls below approximately 2.3 V, the device stops switching, and the PFET operates as a current source
limiting the current to typically 350 mA. This prevents damage to the LM3554 and excessive current draw from
the battery during output short circuit conditions.
7.3.4 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 pulseonly terminates 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).
7.3.5 Flash Termination (I2C-Initiated Flash)
For I2C-initiated 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.
7.3.6 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 32 ms giving a flash timeout range of 32 ms to 1024 ms
(see Table 4).
7.3.7 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 ramp up to the programmed torch current level by stepping through all of the torch
currents at 16 µs/step until the programmed torch current level is reached.
7.3.8 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 ramps
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 turns 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) takes precedence over the TORCH mode input. Figure 37 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 section of the datasheet.
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Feature Description (continued)
7.3.9 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.
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 ramps 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 5, Figure 33, and Figure 34 detail the Functionality of the
ENVM/TX2 input.
7.3.9.1 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). To configure the LM3554 for this feature:
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 (1.05 V 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.
7.3.10 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.
7.3.10.1 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 (2.3 mA, 4.6 mA, 6.9 mA, 8.2 mA). Bits [7:6] of the Torch Brightness Register
set the 4 different indicator current levels. The LEDI current source has a 1-V typical headroom voltage.
7.3.10.2 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 = 1.05 V 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 the Configuration Register 2 bit [1] = 0, the LM3554 is forced into
torch mode when the voltage at LEDI/NTC falls below VTRIP. With the Configuration Register 2 bit [1] = 1 the
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Feature Description (continued)
device shuts 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 goes through a 250-µs deglitch
time before the flash current falls to either torch mode or goes into shutdown.
7.3.11 Alternative External Torch (AET Mode)
Configuration Register 2 bit [2] programs the LM3554 for AET 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 is forced into torch mode only for the duration of the timeout counter. At the
end of the timeout counter the LEDs turn off.
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 turn off at the end of the timeout
duration. (See LM3554 Timing Diagrams, Figure 35, and Figure 36.)
7.3.12 Input Voltage Monitor
The LM3554 has an internal comparator that monitors the voltage at IN, which 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 1 and 2 program the four adjustable
thresholds of 3.1 V, 3.2 V, 3.3 V, and 3.4 V. Bit 3 in Configuration Register 2 (0xF0) selects whether an
undervoltage event forces torch mode or forces the LEDs off. See /Table 7 and /Table 9 for additional
information.
There is a set 100-mV hysteresis for the input voltage monitor. When the input voltage monitor is active, and VIN
falls below the programmed VIN monitor threshold, the LEDs either turn off or their current is 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 100 mV above the UVLO threshold and secondly, the Flags Register must be read back.
7.3.13 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 28. Normal Torch-to-Flash Operation (Default, Power On or LM3554 Reset State)
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Feature Description (continued)
TX1/TORCH
STROBE
Default State
(TX event during a STROBE event)
I FLASH
I TORCH
I LED
Timeout
Duration
Figure 29. TX1 Event During A Flash Event
(Default State,TX1/Torch is an Active High TX Input)
TX1/TORCH
STROBE
Default State
(TX1 event before and after STROBE event)
I TORCH
I LED
Timeout
Duration
Figure 30. 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 31. Strobe Input is Level Sensitive (Default State, STR Bit = 0)
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Feature Description (continued)
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 32. Strobe Input is Edge Sensitive (STR Bit = 1)
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 33. ENVM/TX2 Pin is Configured as an Active High TX Input
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Feature Description (continued)
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 34. 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 35. Alternative External Torch Mode (TX1/Torch Turns on Before Strobe)
TX1/TORCH
Configuration Register 2 bit [2] = 1 (AET)
(STROBE goes high before TX1)
STROBE
IFLASH
ITORCH
I LED
Timeout
Duration
Figure 36. Alternative External Torch Mode
(Strobe Goes High Before TX1/Torch, Same As Default With SEM = 0)
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Feature Description (continued)
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 37. TX1/Torch Configured as a Hardware Torch Input
7.3.14 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 TX1 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.
7.3.15 Thermal Shutdown
When the device 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 is written to bit [1] of the Flag Register (Thermal Shutdown bit). The LM3554 starts 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
device turns off and starts up again after the die temperature cools, resulting in a pulsed on/off operation. The
OVT bit, however, is only written once. To reset the OVT bit pull HWEN low, power down the LM3554, or read
the Flags Register.
7.3.16 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 500 mV while the device is in torch or flash mode.
There is a delay of 250 µs before the LEDF flag is valid on a LED short. This is the time from when VLED falls
below the LED short threshold of 500 mV (typical) to when the fault flag is valid. There is a delay of 2 µs 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.
7.3.17 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 device, reading the Flags Register, or when the next flash pulse is triggered.
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Feature Description (continued)
7.3.18 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 (1.05 V 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) for more details.)
7.3.19 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.
7.3.20 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 is 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 reads 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 Table 6).
7.3.21 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
operates 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.
7.4 Device Functional Modes
7.4.1 Flash Mode
In flash mode the LED current sources (LED1 and LED2) each provide 16 different current levels from typically
34 mA to approximately 600 mA. 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) ramps up to the programmed Flash current by stepping through
all Flash levels (16 µs/step) until the programmed current is reached.
7.4.2 Pass Mode
Once the output voltage charges up to VIN – 150 mV the the device operates either in pass mode or boost mode.
If the voltage difference between VOUT and VLED is less than 300 mV, the device transitions in boost mode. If the
difference between VOUT and VLED is greater than 300 mV, the device operates in pass mode. In pass mode the
boost converter stops switching, and the synchronous PFET turns fully on bringing VOUT up to VIN – IIN × RPMOS
(RPMOS = 150 mΩ). 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.
7.4.3 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 (4.5 V and 5 V). Write a 1 to bit 1 (OV) of Configuration Register 1 to
set VOUT to 5 V. Write a 0 to this bit to set VOUT to 4.5 V. In voltage-output mode the LED current sources can
continue to operate; however, the difference between VOUT and VLED is dropped across the current sources. (See
Maximum Output Power.) In voltage-output mode when VIN is greater than VOUT the LM3554 device operates in
pass mode (see Pass Mode).
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Device Functional Modes (continued)
At light loads the LM3554 switches over to a pulsed frequency mode operation (light load comparator enabled).
In this mode the device only switches 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.
7.5 Programming
7.5.1 I2C-Compatible Interface
7.5.1.1 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 38. Start and Stop Sequences
The I2C bus is considered busy after a START condition and free after a STOP condition. During data
transmission the I2C master can generate repeated START conditions. A START and a repeated START
condition are equivalent function-wise. The data on SDA must be stable during the HIGH period of the clock
signal (SCL). In other words, the state of SDA can only be changed when SCL is LOW. Figure 1 and Figure 39
show the SDA and SCL signal timing for the I2C-Compatible Bus. See Electrical Characteristics for timing values.
t1
SCL
t5
t4
SDA_IN
t2
SDA_OUT
t3
Figure 39. I2C-Compatible Timing
7.5.1.2 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.
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Programming (continued)
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 40. Device Address
7.5.1.3 Transferring Data
Every byte on the SDA line must be eight bits long, with the most significant bit (MSB) transferred first. Each byte
of data must be followed by an acknowledge bit (ACK). The acknowledge related clock pulse (9th clock pulse) is
generated by the master. The master 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.
7.6 Register Maps
7.6.1 Register Descriptions
Table 1. LM3554 Internal Registers
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
7.6.1.1 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
TC2
Bit 5
TC1
Bit 4
TC0
Bit 3
LSB
VM
Bit 2
EN1
Bit 1
EN0
Bit 0
Torch Brightness Register Description
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Table 2. Torch Brightness Register Bit Settings
Bit 7 (IND1)
Bit 6 (IND0)
Indicator Current Select Bits
00 = 2.3 mA
01 = 4.6 mA (default state)
10 = 6.9 mA
11 = 8.2 mA
Bit 5 (TC2)
Bit 4 (TC1)
Bit 3 (TC0)
Torch Current Select Bits
000 = 17 mA (34 mA total)
001 = 35.5 mA (71 mA total)
010 = 54 mA (108 mA total) default state
011 = 73 mA (146mA total)
100 = 90 mA (180mA total)
101 = 109 mA (218 mA total)
110 = 128 mA (256 mA total)
111 = 147.5 mA (295 mA total)
Bit 2 (VM)
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)
7.6.1.2 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
FC1
Bit 4
FC2
Bit 5
FC0
Bit 3
LSB
VM
Bit 2
EN1
Bit 1
EN0
Bit 0
Flash Brightness Register Description
Table 3. Flash Brightness Register Bit Settings
Bit 7 (STR)
Bit 6 (FC3)
STROBE Edge or Level
Select
0 = (Level Sensitive) When
STROBE goes high, flash
current turns 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 turns on and remain
on for the duration of the
Flash Timeout.
Bit 5 (FC2)
Bit 4 (FC1)
Bit 3 (FC0)
Bit 2 (VM)
Flash Current Select Bits
0000 = 35.5 mA (71 mA total)
0001 = 73 mA (146 mA total)
0010 = 109 mA (218 mA total)
0011 = 147.5 mA (295 mA total)
0100 = 182.5 mA (365 mA total)
0101 = 220.5 mA (441 mA total)
0110 = 259 mA (518 mA total)
111 = 298 mA (596 mA total)
1000 =326 mA (652 mA total)
1001 = 364.5 mA (729 mA total)
1010 = 402.5 mA (805 mA total)
1011 = 440.5 mA (881 mA total)
1100 = 480 mA (960 mA total)
1101 = 518.5 mA (1037 mA total) Default
1110 = 556.5 mA (1113 mA total)
1111 = 595.5 mA (1191 mA 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)
7.6.1.3 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
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 = 1-A peak current limit
01 = 1.5-A peak current limit
10 = 2-A peak current limit
(default)
11 = 2.5-A peak current limit
Bit 4 (T4)
Bit 3 (T3)
Bit 2 (T2)
Bit 1 (T1)
Bit 0 (T0)
Flash Timeout Select Bits
00000 = 32-ms timeout
00001 = 64-ms timeout
00010 = 96-ms timeout
00011 = 128-ms timeout
00100 = 160-ms timeout
00101 = 192-ms timeout
00110 = 224-ms timeout
00111 = 256-ms timeout
01000 = 288-ms timeout
01001 = 320-ms timeout
01010 = 352-ms timeout
01011 = 384-ms timeout
01100 = 416-ms timeout
01101 = 448-ms timeout
01110 = 480-ms timeout
01111 = 512-ms timeout (default)
10000 = 544-ms timeout
10001 = 576-ms timeout
10010 = 608-ms timeout
10011 = 640-ms timeout
10100 = 672-ms timeout
10101 = 704-ms timeout
10110 = 736-ms timeout
10111 = 768-ms time-out
11000 = 800-ms timeout
11001 = 832-ms timeout
11010 = 864-ms timeout
11011 = 896-ms timeout
11100 = 928-ms timeout
11101 = 960-ms timeout
11110 = 992-ms timeout
11111 = 1024-ms timeout
7.6.1.4 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 and Table 5.)
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
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)
Bit 1 (Thermal
Shutdown)
0 = No Fault at
Not Used
VIN (default) (Reads Back 1
)
0 = LEDI/NTC 0 = ENVM/TX2
pin is above
has not
VTRIP (default) changed state
(default)
0 = TX1/TORCH
has not changed
state (default)
0 = Proper
LED Operation
(default)
1 = Input
Voltage
Monitor is
enabled and
VIN has fallen
below the
programmed
threshold
1 = LEDI/NTC
has fallen
below
VTRIP(NTC
mode only)
1 = TX1/TORCH
pin has changed
state (TX1 mode
only)
1 = LED Failed
(Open or Short
1 = ENVM/TX2
has changed
state (TX2
mode only)
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
7.6.1.5 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 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
Configuration Register 1 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
forces voltageoutput mode
(default)
Reads Back '0'
0 = LEDI/NTC
pin in Indicator
mode (default)
0 = STROBE
Input Enabled
(default)
0 = Voltage
Mode output
voltage is 4.5 V
0 = Light load
comparator is
enabled. The
LM3554 goes
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
forces 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 5 V
(default)
1 = Light load
comparator is
disabled. The
LM3554 does
not go into PFM
mode at light
load.
26
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7.6.1.6 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 AET mode (see 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
NTC
Shutdown
Bit 1
TX2
Shutdown
Bit 0
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)
7.6.1.7 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. 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
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 pulls 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
7.6.1.8 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. 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
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 = 3.1-V threshold (VIN falling)
Default
01=3.2-V threshold (VIN falling)
10 = 3.3-V threshold (VIN falling)
11 = 3.4-V threshold (VIN falling)
Bit 0 (VIN
Monitor Enable)
0 = VIN
Monitoring
Comparator is
disabled
(default)
1 = VIN
Monitoring
Comparator is
enabled.
28
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LM3554 is a dual-string white-LED driver for LED camera flash applications. The dual high-side current
sources allow for grounded cathode LEDs. The integrated boost provides the power for the current sources and
can source up to 1.2 A from a single-cell Li+ voltage range.
8.2 Typical Application
2.2 µH
SW
IN
2.5 V ± 5.5 V
OUT
Optional fixed 4.5-V or 5-V DC
power rail or adaptive mode for
white LED bias
4.7 µF
HWEN
SCL
SDA
LM3554
4.7 µF
VBIAS
LED1
LED2
STROBE
TX1/TORCH/
LEDI/NTC
GPIO1
ENVM/TX2
/GPIO GND
D2
Flash
LEDs
D1
Indicator
LED
RBIAS
2 NŸ
Thermistor
0.1 µF
Figure 41. LM3554 Typical Application
8.2.1 Design Requirements
For typical LM3554 device applications, use the parameters listed in Table 10.
Table 10. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Minimum input voltage
2.5 V
Programmable output voltage
4.5 V or 5 V
Programmable output current
37.5 mA to 1.2 A
Table 11. Application Circuit Component List
COMPONENT
MANUFACTURER
VALUE
PART NUMBER
SIZE (mm)
RATING
L
TOKO
2.2 µH
FDSE0312-2R2M
3 × 3 × 1.2
2.3 A (0.2 Ω)
4.7 µF/10 µF
Murata
GRM188R60J475M,
or
GRM188R60J106M
0603 (1.6 × 0.8 ×0.8 )
COUT
CIN
Murata
GRM185R60J475M
0603 (1.6 × 0.8 × 0.8
)
LEDs
Lumiled
4.7 µF
LXCL-PWF4
6.3 V
6.3 V
1.5 A
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8.2.2 Detailed Design Procedure
8.2.2.1 Output Capacitor Selection
The LM3554 is designed to operate with a at least a 4.7-µF ceramic output capacitor in LED mode and a 10-µF
output capacitor in voltage-output mode. When the boost converter is running the output capacitor supplies the
load current during the boost converters on-time. When the NMOS switch turns off the inductor energy is
discharged through the internal PMOS switch supplying power to the load and restoring charge to the output
capacitor. This causes a sag in the output voltage during the on time and a rise in the output voltage during the
off time. The output capacitor is therefore chosen to limit the output ripple to an acceptable level depending on
load current and input/output voltage differentials and also to ensure the converter remains stable.
For proper LED operation the output capacitor must be at least a 4.7-µF ceramic (10-µF in voltage-output mode).
Larger capacitors such as 10 µF or 22 µF can be used if lower output voltage ripple is desired. To estimate the
output voltage ripple considering the ripple due to capacitor discharge (ΔVQ) and the ripple due to equivalent
series resistance (ESR) of the capacitor (ΔVESR) use Equation 1 and Equation 2:
For continuous conduction mode, the output voltage ripple due to the capacitor discharge is:
'VQ =
ILED x (VOUT - VIN)
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·
VIN
¹
+ 'I L
VIN x (VOUT - VIN )
2 x f SW x L x VOUT
(2)
In ceramic capacitors the ESR is very low, thus the assumption is that that 80% of the output voltage ripple is
due to capacitor discharge and 20% from ESR. Table 12 lists different manufacturers for various output
capacitors and their case sizes suitable for use with the LM3554.
8.2.2.2 Input Capacitor Selection
Choosing the correct size and type of input capacitor helps minimize the voltage ripple caused by the device
boost converter switching and reduces noise on the devices input terminal that can feed through and disrupt
internal analog signals. In the Figure 41 a 4.7-µF ceramic input capacitor works well. It is important to place the
input capacitor as close to the device input (IN) terminals as possible. This reduces the series resistance and
inductance that can inject noise into the device due to the input switching currents. Table 12 lists various input
capacitors that or recommended for use with the LM3554.
Table 12. Recommended Input/Output Capacitors (X5R Dielectric)
30
MANUFACTURER
PART NUMBER
VALUE
CASE SIZE (mm)
VOLTAGE RATING
TDK Corporation
C1608JB0J475K
4.7 µF
0603 (1.6 × 0.8 × 0.8 )
6.3 V
TDK Corporation
C1608JB0J106M
10 µF
0603 (1.6 × 0.8 × 0.8 )
6.3 V
TDK Corporation
C2012JB1C475K
4.7 µF
0805 (2 ×1.25 ×1.25)
16 V
TDK Corporation
C2012JB1A106M
10 µF
0805 (2 ×1.25 ×1.25)
10 V
TDK Corporation
C2012JB0J226M
22 µF
0805 (2 ×1.25 ×1.25)
6.3 V
Murata
GRM188R60J475KE19
4.7 µF
0603 (1.6 × 0.8 × 0.8 )
6.3 V
Murata
GRM21BR61C475KA88
4.7 µF
0805 (2 ×1.25 ×1.25)
16 V
Murata
GRM21BR61A106KE19
10 µF
0805 (2 ×1.25 ×1.25)
10 V
Murata
GRM21BR60J226ME39L
22 µF
0805 (2 ×1.25 ×1.25)
6.3 V
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8.2.2.3 Inductor Selection
The LM3554 is designed to use a 2.2-µH inductor. Table 13 lists various inductors and their manufacturers that
can work well with the LM3554. When the device is boosting (VOUT > VIN) the inductor is typically 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 must 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:
IPEAK =
I LOAD VOUT
V x (VOUT - VIN)
x
+ 'IL where 'IL = IN
K
VIN
2 x f SW x L x VOUT
where
•
•
ƒSW = 2 MHz
η can be found in Typical Characteristics
(3)
Table 13. Recommended Inductors
MANUFACTURER
L
PART NUMBER
DIMENSIONS
(L×W×H)(mm)
ISAT
TOKO
2.2 µH
FDSE0312-2R2M
3 × 3 ×1.2
2A
TDK
2.2 µH
VLS252012T-2R2M1R3
2 × 2.5 ×1.2 mm
1.5 A
Coilcraft
2. 2µH
LPS4018-222ML
3.9 × 3.9 × 1.7 mm
2.3 A
8.2.2.4 NTC Thermistor Selection
NTC thermistors have a temperature to resistance relationship of:
E
R(T) = R25°C x e
§ 1 - 1·
©T °C+ 273 298¹
where
•
•
β is given in the thermistor datasheet
R25C is the thermistors value at 25°C
(4)
Figure 43 is chosen so that it is equal to:
R3 =
RT( TRIP) (VBIAS - VTRIP )
VTRIP
where
•
•
•
R(T)TRIP is the thermistor value at the temperature trip point
VBIAS is shown in Figure 43
VTRIP = 1.05V (typical)
(5)
Choosing R3 here gives a more linear response around the temperature trip voltage. For example, with VBIAS =
2.5 V, a thermistor whose nominal value at 25°C is 100 kΩ and a β = 4500 K, 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
(6)
Figure 42 shows the linearity of the thermistor resistive divider of the previous example.
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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 42. 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 is shown in Equation 7:
E x 298 °C
- 273°C
T( °C) =
VTRIP x R3
ª
º
E
298°C x LN
«(VBIAS - VTRIP ) x R25 °C» +
¬
¼
(7)
®
Using, for example, Excel spreadsheet software, 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.
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 43 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.
32
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Internal to
LM3554
TX2
VIN Monitor
TX1/TORCH
Force Torch or
LED Shutdown (VIN Monitor, TX2 or
NTC only)
VBIAS
1.05V
LEDI/
NTC
R3
+
R(T)
0.1 PF
Figure 43. Thermistor Voltage Divider and Sensing Circuit
8.2.2.5 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. Consequently, the noisy environment generated from the boost
converter switching can introduce noise from GND into the thermistor sensing input. To filter out this noise it is
necessary to place a 0.1-µF 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 to the PGND pin of the device as possible.
8.2.2.6 Maximum Load Current (Voltage Mode)
Assuming the power dissipation in the LM3554 and the ambient temperature are such that the device does not
hit thermal shutdown, the maximum load current as a function of IPEAK is:
I LOAD =
(I PEAK - 'IL) x K x VIN
VOUT
where
•
η is efficiency and is found in the efficiency curves in the Typical Characteristics
(8)
and
'IL =
VIN x (VOUT - VIN )
2 x fSW x L x VOUT
(9)
Figure 44 shows the theoretical maximum output current vs theoretical efficiency at different input and output
voltages using Equation 8 and Equation 9 for ΔIL and ILOAD with a peak current of 2.5 A. Figure 44 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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LM3554
Maximum Output Current (A)
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Maximum Output Current vs Efficiency
(I PEAK = 2.5A)
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
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 44. LM3554 Maximum Output Current
8.2.2.7 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 6 W. However, any appreciable output current causes 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 because 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.
8.2.2.7.1 Voltage-Output Mode
In voltage-output mode the total power dissipated in the LM3554 can be approximated as:
PDISS = PN + PP + PLED1 + PLED2 + PIND
where
•
•
•
PN is the power lost in the NFET
PP is the PFET power loss
PLED1, PLED2, and PIND are the losses across the current sink
(10)
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
(11)
Equation 11 consider the average current through the NFET and PFET. The actual power losses are higher due
to the RMS currents and the quiescent power into IN. These, however, can give a decent approximation.
8.2.2.7.2 LED Boost Mode
In LED mode with VOUT > VIN the device boost converter switches and make VOUT = VLED + 0.3 V. 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
(12)
8.2.2.7.3 LED Pass Mode
In LED mode with VIN – ILOAD × RPFET > VLED + 0.3 V, 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 are 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
(13)
Once the total power dissipated in the LM3554 is calculated the ambient temperature and the thermal resistance
of the 16-pin DSBGA (YFQ package) are used to calculate the total die temperature (or junction temperature TJ).
As an example, assume the LM3554 is operating at VIN = 3.6 V and configured for voltage-output mode with
VOUT = 5 V and IOUT = 0.7 A. The LED currents are then programmed in torch mode with 150 mA each at VLED =
3.6 V. Additionally, the indicator LED has 10 mA at VIND = 3.6 V. Using Equation 12 and Equation 13 above, the
approximate total power dissipated in the device is:
PDISS = 139 mW + 357 mW + 420 mW + 14 mW = 930 mW
(14)
The die temperature approximation is:
TJ
0.93W u 75.8qC/W + 25qC = 95.5qC
(15)
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-to-ambient
thermal resistance. In this example a thermal resistance of 75.8°C/W was used (JESD51-7 standard). Because
thermal resistance from junction-to-ambient is largely PCB layout dependent, the actual number used likely may
be different and must be taken into account when performing these calculations.
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8.2.3 Application Curves
Single LED
Dual LEDs
Figure 45. LED Efficiency vs VIN
Figure 46. LED Efficiency vs VIN
Single LED
Single LED
Figure 48. LED Efficiency vs VIN
Figure 47. Input Current vs VIN
Dual LEDs
L = Coilcraft LPS4018-222
Single LED
L = Coilcraft LPS4018-222
Figure 50. Input Current vs VIN
Figure 49. LED Efficiency vs VIN
36
L = Coilcraft LPS4018-222
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VOUT = 5 V
Voltage-Output Mode
VOUT = 5 V
Figure 51. Efficiency vs IOUT
Time Base: 100 µs/div
Ch 1: VOUT (2 V/div)
Ch 4: ILED (500 mA/div)
Figure 52. Efficiency vs VIN
IFLASH = 1.2 A
Single LED
Ch 2: IL (500 mA/div)
Ch 3: STROBE (5 V/div)
Figure 53. Start-Up Into Flash Mode
Time Base: 100 µs/div
Ch 1: VOUT (5 V/div)
Ch 4: ILED (500 mA/div)
Voltage-Output Mode
IFLASH = 1.2 A
ITORCH = 295 mA
Ch 2: IL (1 A/div)
Single LED
Ch 3: STROBE (5 V/div)
Figure 55. Torch Mode to Flash Mode Transition
Time Base: 100 µs/div
90-mA Torch Setting
Chl 1: VOUT (2 V/div)
Ch 4: ILED (100 mA/div)
ITORCH = 180 mA
Single LED
Ch 2: IL (500 mA/div)
Ch 3: TX1 (5 V/div)
Figure 54. Start-Up Into Hardware Torch Mode
Time Base: 20 µs/div
Ch 1: VOUT (2 V/div)
Ch 4: ILED (500 mA/div)
IFLASH = 1.2 A
ITORCH = 180 mA
Ch 2: IL (1 A/div)
Single LED
Ch 3: TX1 (5 V/div)
Figure 56. TX1 Interrupt Operation, TX1 Rising
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Time Base: 20 µs/div
Ch 1: VOUT (2 V/div)
Ch 4: ILED (500 mA/div)
Ch 3: TX1 (5 V/div)
IFLASH = 1.2 A
Ch 2: IL (1 A/div)
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ITORCH = 180 mA
Single LED
Time Base: 400 µs/div
Ch 3: VIN (5 V/div)
Ch 4: ILED (500 mA/div)
Figure 57. TX1 Interrupt Operation, TX1 Falling
Time Base: 40 µs/div
Ch 1: VOUT (500 mV/div)
Ch 4: IOUT (500 mA/div)
VIN = 3.6 V
Ch 2: IL (500 mA/div)
VOUT = 5 V
Figure 59. Load Transient (Voltage Output Mode)
Time Base: 20 µs/div
ILED = 1.2 A
Ch 1: VOUT (2 V/div)
Ch 3: HWEN (5 V/div)
Ch 4: ILED (500 mA/div)
Single LED
Figure 61. Flash Pulse to HWEN Low
38
IFLASH = 1.2 A
Ch 2: IL (1 A/div)
Single LED
Figure 58. Line Transient (LED Mode)
Time Base: 200 µs/div
VOUT = 5 V
IOUT = 500 mA
Ch 1: VOUT = (5 V/div)
Ch 2: IL + IIN (500 mA/div)
Ch 3 (Top Trace): VIN (1 V/div)
Figure 60. Line Transient (Voltage Output Mode)
Time Base: 100 µs/div
Ch 1: VOUT (2 V/div)
Ch 4: ILED (500 mA/div)
VOUT = 5 V
Ch 2: IL (1 A/div)
Ch 3: ENVM (5 V/div)
ILED = 1.2 A
Single LED
Figure 62. Flash Pulse to Flash Pulse + VOUT Mode
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Time Base: 100 µs/div
Ch 1: VOUT (2 V/div)
Ch 4: ILED (500mA/div)
ILED = 1.2 A
Ch 2: IL (1 A/div)
Ch 3: ENVM (5 V/div)
VOUT = 5 V
Single LED
Time Base: 200 µs/div
Single LED
Ch 3: NTC pin voltage (5 V/div)
R(T) = 100 kΩ at 25°C
Figure 63. Flash Pulse and VOUT to Flash Pulse
Time Base: 100 ms/div
Ch 3: VIN (1V/div)
ILED = 1.2 A
Ch 4: ILED (500 mA/div)
Circuit of Figure 43
ILED = 1.2 A
Ch 4: ILED (500 mA/div)
R3 = 9 kΩ
Figure 64. NTC Mode Response
3.1-V UVLO Setting
Single LED
Figure 65. VIN Monitor Response
9 Power Supply Recommendations
The LM3554 is designed to operate from an input supply range of 2.5 V to 5.5 V. This input supply must be well
regulated and provide the peak current required by the LED configuration and inductor selected.
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10 Layout
10.1 Layout Guidelines
The high frequency and large switching currents of the LM3554 make the choice of layout important. Use the
following steps 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 turnon and turnoff and can see current
spikes over 1 A in amplitude. Connecting the input capacitor through short wide traces on both the IN and
GND terminals reduces 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 to the OUT and GND pins as possible.
The returns for both CIN and COUT must come together at one point, and as close to the GND pin as
possible. Connecting COUT through short wide traces reduces the series inductance on the OUT and GND
pins that can corrupt the VOUT and GND lines and cause excessive noise in the device and surrounding
circuitry.
3. Connect the inductor on the top layer close to the SW pin. There must be a low impedance connection from
the inductor to SW due to the large DC inductor current, and at the same time the area occupied by the SW
node must be small to reduce the capacitive coupling of the high dV/dt present at SW that can couple into
nearby traces.
4. Avoid routing logic traces near the SW node 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
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 device. If possible, route the LED returns
with a dedicated path to keep the high amplitude LED currents out the GND plane. For flash LEDs that are
routed relatively far away from the device, a good approach is to sandwich the forward and return current
paths over the top of each other on two layers. This helps reduce the inductance of the LED current paths.
6. The NTC thermistor is intended to have its return path connected to the LED 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 because both the LED and the thermistor
are electrically connected at GND. The drawback is that the thermistor return detects the switching currents
from the boost converter of the LM3554. Because of this, it is necessary to have a filter capacitor at the NTC
pin which terminates close to the device GND and which can conduct the switched currents to GND.
10.2 Layout Example
5.1 mm
4.5 mm
HWEN
ENVM/TX2/GPIO2
/TORCH/GPIO1
Figure 66. LM3554 Layout Example
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11 Device and Documentation Support
11.1 Device Support
11.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.2 Documentation Support
11.2.1 Related Documentation
For additional information, see the following:
AN1112 DSBGA Wafer Level Chip Scale Package (SNVA009)
11.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.4 Trademarks
E2E is a trademark of Texas Instruments.
Excel is a registered trademark of Microsoft Corp..
All other trademarks are the property of their respective owners.
11.5 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
11.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM3554TME/NOPB
ACTIVE
DSBGA
YFQ
16
250
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-30 to 85
SF
LM3554TMX/NOPB
ACTIVE
DSBGA
YFQ
16
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-30 to 85
SF
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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