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LM3555
SNVS594G – DECEMBER 2008 – REVISED APRIL 2016
LM3555 Synchronous Boost Converter With 500-mA High-Side
LED Driver and Dual-Mode Control Interface
1 Features
3 Description
•
The LM3555 is a 2-MHz fixed-frequency, currentmode synchronous boost converter designed to drive
either a single flash LED at 500 mA or two series
flash LEDs at 400 mA. A high-voltage current source
allows the LEDs to be terminated to the GND plane
eliminating the need for an additional return trace
back to the device.
1
•
•
•
•
•
•
•
•
•
•
•
High-Voltage High-Side Current Source Allows for
Grounded Cathode LED Operation
Synchronous Boost Converter
Peak Converter Efficiency > 90%
Accurate and Programmable LED Current
Ranging From 60 mA to 500 mA
Adaptive LED Current Range Based on LED
Configuration
Dedicated Indicator Current Source
Dedicated Torch and Strobe Pins
Dual Mode Control (General Purpose or I2C)
Broken Inductor Detection
Output Overvoltage Protection
Output and LED Short-Circuit Protection
400-kHz I2C-Compatible Interface
A dual-mode control interface allows the user to
configure the LM3555 with a general-purpose
interface using two enable pins for control or an I2C
allowing a higher level of control. Both interfaces
allow access to the indicator, assist light, and flash
modes. A dedicated STROBE pin provides a direct
interface to trigger the flash event, while an external
TORCH pin provides an additional method for
enabling the LEDs in a constant current mode.
The LM3555 can adaptively scale the maximum flash
level delivered to the LEDs based upon the flash
configuration, whether it be a single LED or two LEDs
in series.
2 Applications
Camera Phone LED Flash
Eight protection features are available on the LM3555
ranging from overvoltage protection to broken
inductor detection. The LM3555 has four selectable
inductor current limits to help the user select an
inductor that is appropriate for the design.
Device Information(1)
PART NUMBER
LM3555
PACKAGE
DSBGA (12)
BODY SIZE (MAX)
2.09 mm × 1.565 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Application
2.2 µH
CIN
10 µF
SW
VIN
VOUT
+
VBAT
COUT
10 µF
STROBE
TORCH
I2C/EN
VLED
LM3555
SCL/EN1
SDA/EN2
PGND
SGND
IND
Copyright © 2016, Texas Instruments Incorporated
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.
LM3555
SNVS594G – DECEMBER 2008 – REVISED APRIL 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
5
5
7
8
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Control Interface Timing Requirements ....................
Typical Characteristics ..............................................
Detailed Description ............................................ 15
7.1
7.2
7.3
7.4
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
15
15
16
19
7.5 Programming........................................................... 22
7.6 Register Maps ......................................................... 24
8
Application and Implementation ........................ 27
8.1 Application Information............................................ 27
8.2 Typical Application ................................................. 27
9 Power Supply Recommendations...................... 30
10 Layout................................................................... 31
10.1 Layout Guidelines ................................................. 31
10.2 Layout Example .................................................... 31
11 Device and Documentation Support ................. 32
11.1
11.2
11.3
11.4
11.5
11.6
Device Support......................................................
Documentation Support ........................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
32
32
32
32
32
32
12 Mechanical, Packaging, and Orderable
Information ........................................................... 32
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision F (November 2013) to Revision G
Page
•
Added Device Information and Pin Configuration and Functions sections, ESD Ratings 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
•
Changed RθJA value; add rest of Thermal Information ........................................................................................................... 5
Changes from Revision E (November 2011) to Revision F
•
2
Page
Changed layout of National Data Sheet to TI format ........................................................................................................... 31
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SNVS594G – DECEMBER 2008 – REVISED APRIL 2016
5 Pin Configuration and Functions
YZR Package
12-Pin DSBGA
Top View
YZR Package
12-Pin DSBGA
Bottom View
A1
A2
A3
A3
A2
A1
B1
B2
B3
B3
B2
B1
C1
C2
C3
C3
C2
C1
D1
D2
D3
D3
D2
D1
Pin Functions
PIN
I/O
DESCRIPTION
NUMBER
NAME
A1
PGND
—
Power ground
A2
SGND
—
Signal ground
A3
VIN
I
B1
SW
—
B2
TORCH
I
Torch pin. Driving this pin high enables torch mode.
B3
IND
O
Red indicator LED current source. Connect to RED LED anode
C1
VOUT
O
Boost output. Connect output bypass capacitor very close to this pin
C2
STROBE
I/O
Strobe signal input pin to synchronize flash pulse in I2C mode. This signal usually comes
from the camera processor. In simple logic mode this pin, when tied to a voltage rail
through a pullup resistor indicates the number of LEDs in the system.
C3
I2C / EN
I
I2C / EN-logic selection. High = I2C mode, Low = simple logic mode.
D1
VLED
O
LED current source. Connect to the anode of the flash LED. One or two LEDs can be
connected in series.
D2
SDA / EN2
I/O
EN2 signal pin in simple logic mode. I2C data signal in I2C mode.
D3
SCL / EN1
I
EN1 signal pin in simple logic mode. I2C clock signal in I2C mode.
Input voltage pin of the device. Connect input bypass capacitor very close to this pin.
Inductor connection
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SNVS594G – DECEMBER 2008 – REVISED APRIL 2016
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1) (2) (3)
MIN
MAX
UNIT
VIN
−0.3
6
V
TORCH, IND, STROBE, I2C/EN, SDA/EN2, SCL/EN1
−0.3
(VIN + 0.3 V) w/ 6 V
maximum
V
12
V
10
V
SW
VOUT, VLED
Continuous power dissipation (4)
Internally limited
Junction temperature, TJ-MAX
Maximum lead temperature (soldering)
See
Storage temperature, Tstg
(1)
(2)
(3)
(4)
(5)
150
°C
150
°C
(5)
–55
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). Thermal shutdown is specified by design.
For detailed soldering specifications and information, please refer to AN-1112 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 (1)
VALUE
UNIT
±2500
V
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) (2)
MIN
MAX
2.5
5.5
V
Junction temperature, TJ
−30
125
°C
Ambient temperature, TA (3)
−30
85
°C
Input voltage
(1)
(2)
(3)
4
UNIT
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Recommended Operating Ratings are
conditions under which operation of the device is specified. Operating Ratings do not imply specified performance limits. For specified
performance limits and associated test conditions, see the Electrical Characteristics tables.
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 de-rated. 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).
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6.4 Thermal Information
LM3555
THERMAL METRIC (1)
YZR (DSBGA)
UNIT
12 PINS
RθJA
Junction-to-ambient thermal resistance
92.9
°C/W
RθJC(top)
RθJB
Junction-to-case (top) thermal resistance
0.6
°C/W
Junction-to-board thermal resistance
16.1
°C/W
ψJT
Junction-to-top characterization parameter
2.8
°C/W
ψJB
Junction-to-board characterization parameter
16.1
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
6.5 Electrical Characteristics
Unless otherwise specified: typical limits are for TA = 25°C; minimum and maximum limits apply over the full operating
ambient temperature range (−30°C ≤ TA ≤ +85°C); VIN = 3.6 V. (1) (2)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
50.7
(–15.5%)
60
67.2
(12%)
69.8
(–12.8%)
80
86.4
(8%)
304
(–5%)
320
336
(5%)
475
(–5%)
500
535
(7%)
–20.4%
2.5 mA
33.6%
–20.4%
5 mA
33.8%
–20.3%
7.5 mA
33.7%
–20.2%
10 mA
33.4%
300
350
9.5
9.96
UNIT
CURRENT AND VOLTAGE SPECIFICATIONS
ILED-OUT
IIND-OUT
Flash LED accuracy
Indicator LED current
accuracy
2.7 V ≤ VIN ≤ 5.5 V
VOUT = 6.5 V,
VLED = 6.2 V
2.7 V ≤ VIN ≤ 5.5 V, VIND = 2 V (indicator mode)
mA (%)
VCSH
Current source
headroom voltage
2.7 V ≤ VIN ≤ 5.5 V
VOVP
Overvoltage Protection
Range
2.7 V ≤ VIN ≤ 5.5 V
VOUT
Output voltage range
(VLED × NLED) + VCSH
ISD
Shutdown current
2.7 V ≤ VIN ≤ 5.5 V
ISB
Standby current
2.7 V ≤ VIN ≤ 5.5 V
1.1
IQ
Operating quiescent
current
2.7 V ≤ VIN ≤ 5.5 V, device switching
3.5
mA
VREF
Reference Voltage for
LED Detection
VIN = 3.6 V (No Offset)
4.35
V
VIND
Indicator Fault Voltages
UVLO
Undervoltage lockout
Falling VIN
2.35
2.4
2.43
UVLOHYST
UVLO hysteresis
Rising VIN
60
70
85
(1)
(2)
Trip point (rising)
9.22
Hysteresis
0.4
Upper range
8.5
Lower range
2.8
IND OVP
V
V
0.75
µA
4.3
µA
2.571
IND Short
mV
0.842
V
V
mV
Minimum (MIN) and maximum (MAX) limits are specified by design, test, or statistical analysis. Typical (TYP) numbers are not specified,
but do represent the most likely norm. Unless otherwise specified, conditions for typical specifications are: VIN = 3.6 V and TA = 25°C.
Switching disabled.
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Electrical Characteristics (continued)
Unless otherwise specified: typical limits are for TA = 25°C; minimum and maximum limits apply over the full operating
ambient temperature range (−30°C ≤ TA ≤ +85°C); VIN = 3.6 V.(1)(2)
PARAMETER
ILIM
Peak current limit
TEST CONDITIONS
2.7 V ≤ VIN ≤ 5.5 V
(3)
MIN
TYP
MAX
Current limit register
value = 00
1.183
1.250
1.55
Current limit register
value = 01
1.417
1.500
1.781
Current limit register
value = 10
1.512
1.750
2.025
Current limit register
value = 11
1.805
2
2.267
1.91
(−4.5%)
2
2.15
(7.5%)
UNIT
A
OSCILLATOR AND TIMING SPECIFICATIONS (NON-I2C INTERFACE TIMING)
ƒSW
Switching frequency
2.7 V ≤ VIN ≤ 5.5 V
tHW
Hardware flash timeout
Default timer
tRU
Current ramp-up time
ILED = 0mA to ILED = fullscale,
VOUT = 6.5 V, VLED = 6.2 V
0.6
1
msec
tRD
Current ramp down time
ILED = fullscale to ILED = 0 mA
VOUT = 6.5 V, VLED = 6.2 V
0.2
0.5
msec
tTORCH-DG
Torch deglitching time
11.7
msec
850
6.3
9
MHz
msec
CONTROL INTERFACE VOLTAGE SPECIFICATIONS
VI2C/EN
I2C/EN pin voltage
threshold
2.7 V ≤ VIN ≤ 5.5 V
VIL
Low-level threshold
voltage (SCL/EN1 and
SDA/EN2)
2.7 V ≤ VIN ≤ 5.5 V
VIH
High-level threshold
voltage (SCL/EN1 and
SDA/EN2)
2.7 V ≤ VIN ≤ 5.5 V
VOL
Low-level output
threshold limit
(SDA/EN2)
ILOAD = 3 mA
(3)
6
Simple mode
2
I C mode
0.54
1.26
0.54
1.26
V
V
V
0.4
V
TA (minimum) = 0°C to account for self-heating. Current Limit specification uses VIN (maximum) = 4 V to account for the input voltage
range where current limit could be reached based upon the maximum application specifications for output voltage and diode current.
Operation above 4 V and up to 5.5 V is allowed and must not reach current limit.
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6.6 Control Interface Timing Requirements
MIN
NOM
MAX
UNIT
250
500
µsec
TI2C-Start
I2C logic start-up time (I2C/EN going high)
ƒSCL
SCL clock frequency
tI2C
I2C hang-up time
tLOW
Low Period of SCL clock
1.3
µsec
tHIGH
High Period of SCL clock
0.6
µsec
tHD-STA
Hold Time (repeated) START condition
0.6
µsec
tSU-STA
Setup time for a repeated START condition
0.6
µsec
tHD-DAT
Data hold time
0
µsec
tSU-DAT
Data setup time
100
nsec
tR
Rise time for SCL and SDA
300
tF
Fall time for SCL and SDA
300
tSU-STO
Setup time for stop condition
0.6
µsec
tBUF
Bus free time between stop and start condition
1.3
µsec
tVD-DAT
Data valid time
0.9
µsec
tVD-ACK
Data valid acknowledge time
0.9
µsec
400
pF
CB
400
35
20 + 0.1 ×
CB
Capacitive load for each bus line
kHz
msec
nsec
nsec
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6.7 Typical Characteristics
0.50
0.48
0.46
0.44
TA = -30°C and +25°C
0.42
0.40
0.38
0.36
0.34
TA = +85°C
0.32
0.30
0.28
0.26
0.24
0.22
0.20
0.18
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0.35
VLED = 6.75V (2 LEDs)
0.34
TA = +25°C
0.33
ILED (A)
ILED (A)
Unless otherwise specified: TA = 25°C; VIN = 3.6 V; CIN1= 10 µF, CIN2= 0.1 µF, COUT = 11 µF; L = 2.2 µH.
0.32
0.31
TA = -30°C
TA = +85°C
0.30
0.29
2.5
3.0
3.5
BRC (#)
5.0
5.5
Two Series LEDs at 320 mA
Figure 1. LED Current vs Brightness Code
1.50
Figure 2. LED Current vs Input Voltage
0.44
VLED = 6.75V (2 LEDs)
ILED = 320 mA
VLED = 6.9V (2 LEDs)
0.43
1.25
0.42
TA = -30°C
1.00
0.41
TA = +25°C
ILED (A)
IIN (A)
4.5
VIN (V)
Two Series LEDs Flash
0.75
TA = -30°C
TA = +25°C
0.40
0.39
0.50
0.38
TA = +85°C
0.25
0.00
2.5
4.0
TA = +85°C
0.37
3.0
3.5
4.0
4.5
5.0
0.36
2.5
5.5
3.0
3.5
4.0
4.5
5.0
5.5
VIN (V)
VIN (V)
Two series LEDs at 320 mA
Two series LEDs at 400 mA
Figure 3. Input Current vs Input Voltage
Figure 4. LED Current vs Input Voltage
0.20
2.00
TA = +85°C
VLED = 6.9V (2 LEDs)
ILED = 400mA
0.18
0.16
1.70
TA = -30°C, +25°C, +85°C
ITORCH (A)
0.14
IIN (A)
1.40
TA = -30°C
1.10
TA = +25°C
0.12
0.10
0.08
0.06
0.80
0.04
0.02
0.50
2.5
3.0
3.5
4.0
4.5
5.0
VIN (V) = 3.6 V, VLED (V) = 6.3 V (2 LEDs)
0.00
0
5.5
VIN (V)
2
3
4
5
BRCTORCH (#)
6
7
2 LEDs
Two Series LEDs at 400 mA
Figure 5. Input Current vs Input Voltage
8
1
Figure 6. Torch Current vs Brightness Code
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Typical Characteristics (continued)
Unless otherwise specified: TA = 25°C; VIN = 3.6 V; CIN1= 10 µF, CIN2= 0.1 µF, COUT = 11 µF; L = 2.2 µH.
0.080
0.100
0.075
0.095
0.070
0.090
TA = -30°C
0.065
0.060
0.055
TA = +25°C
0.080
0.075
0.050
TA = -30°C
0.070
0.045
0.065
VLED (V) = 6.0 V (2 LEDs)
0.040
2.5
3.0
3.5
4.0
4.5
5.0
VLED (V) = 6.1 V (2 LEDs)
0.060
2.5
5.5
3.0
3.5
VIN (V)
4.0
VIN (V)
4.5
5.0
5.5
Two LEDs at 80 mA
Two LEDs at 60 mA
Figure 7. Torch Current vs Input Voltage
Figure 8. Torch Current vs Input Voltage
0.60
0.60
0.55
0.58
TA = -30°C and +25°C
0.50
0.54
0.40
0.52
0.35
TA = +85°C
0.30
VLED = 3.6V
0.56
0.45
ILED (A)
ILED (A)
TA = +25°C
TA = +85°C
0.085
ITORCH (A)
ITORCH (A)
TA = +85°C
TA = -30°C
TA = +25°C
0.50
0.48
0.25
0.46
0.20
0.44
0.15
0.42
0.10
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0.40
2.5
TA = +85°C
3.0
3.5
4.0
BRC (#)
4.5
5.0
5.5
VIN (V)
One LED at 500 mA
Figure 9. Single LED Flash Current vs Brightness Code
1.30
Figure 10. LED Current vs Input Voltage
0.20
VLED = 3.6V
ILED = 500 mA
0.18
1.12
0.16
ITORCH (A)
0.14
IIN (A)
0.94
TA = +25°C
0.76
TA = -30°C
TA = -30°C, +25°C, +85°C
0.12
0.10
0.08
0.06
0.58
0.04
TA = +85°C
VIN (V) = 3.6 V, VLED (V) = 3.0 V
0.02
0.40
2.5
3.0
3.5
4.0
4.5
5.0
0.00
0
5.5
1
2
3
4
5
6
7
BRCTORCH (#)
VIN (V)
One LED
One LED at 500 mA
Figure 11. Input Current vs Input Voltage
Figure 12. Torch Current vs Brightness Code
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Typical Characteristics (continued)
Unless otherwise specified: TA = 25°C; VIN = 3.6 V; CIN1= 10 µF, CIN2= 0.1 µF, COUT = 11 µF; L = 2.2 µH.
0.080
0.100
0.075
0.095
0.090
0.070
TA = +25°C
0.065
ITORCH (A)
ITORCH (A)
TA = +85°C
0.060
0.055
TA = +85°C
0.085
0.080
0.075
TA = -30°C
0.050
TA = -30°C
0.070
0.045
0.065
VLED (V) = 3.0 V
0.040
2.5
3.0
3.5
4.0
4.5
5.0
TA = +25°C
VLED (V) = 3.0 V
0.060
2.5
5.5
3.0
3.5
VIN (V)
One LED at 60 mA
4.0
4.5
VIN (V)
5.0
5.5
One LED at 80 mA
Figure 13. Torch Current vs Input Voltage
Figure 14. Torch Current vs Input Voltage
15.0
12.5
VIND = 2.0 V, Code 3
VIND = 2.0 V, TA = 25°C
12.5
11.5
Code 3
IIND (mA)
IIND (mA)
10.0
7.5
Code 2
TA = +85°C
10.5
TA = -30°C
TA = +25°C
5.0
9.5
Code 1
2.5
Code 0
0.0
2.5
3.0
3.5
4.0
4.5
VIN (V)
5.0
8.5
2.5
5.5
5.5
ICL = 2.0A
VOUT (V) = 8.2V @ 400 mA
9.5
1.75
VLED = 2.0 V
8.5
ICL (A)
IIND (mA)
5.0
2.00
10.5
VLED = 2.4 V
1.25
4.5
ICL = 1.75A
1.50
6.5
5.5
ICL = 1.5A
ICL = 1.25A
1.00
3.5
TA = +25°C, Code 3
3.0
3.5
4.0
4.5
VIN (V)
5.0
0.75
2.5
5.5
3.1
3.7
4.3
4.9
5.5
VIN (V)
Figure 17. Indicator Current vs Input Voltage VLED
10
4.5
2.25
VLED = 1.8 V
2.5
2.5
4.0
Figure 16. Indicator Current vs Input Voltage Tri-Temp
12.5
7.5
3.5
VIN (V)
Figure 15. Indicator Current vs Input Voltage Brightness
Codes
11.5
3.0
Figure 18. Inductor Current Limit vs Input Voltage
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Typical Characteristics (continued)
Unless otherwise specified: TA = 25°C; VIN = 3.6 V; CIN1= 10 µF, CIN2= 0.1 µF, COUT = 11 µF; L = 2.2 µH.
0.50
1.0
VOUT (V) = 8.2V
0.9
0.45
0.8
ISB (μA)
ILED (A)
0.7
0.40
0.35
ICL = 1.5A
3.0
0.4
TA = +25°C
0.2
ICL = 1.75A
TA = -30°C
0.1
ICL = 2.0A
0.25
2.5
0.5
0.3
ICL = 1.25A
0.30
TA = +85°C
0.6
3.5
4.0
4.5
5.0
0.0
2.5
5.5
3.0
3.5
4.0
4.5
5.0
5.5
VIN (V)
VIN (V)
Figure 19. LED Current vs Input Voltage In Current Limit
Figure 20. Shutdown Current vs Input Voltage
2.20
4.0
3.5
2.10
3.0
fSW (MHz)
ISB (μA)
2.5
TA = +85°C
2.0
2.00
1.5
1.90
1.0
TA = -30°C and +25°C
0.5
0.0
2.5
3.0
3.5
4.0
4.5
5.0
1.80
-30 -20 -10 0 10 20 30 40 50 60 70 80 90
5.5
VIN (V)
TA (°C)
Figure 21. Standby Current vs Input Voltage
Figure 22. Frequency vs Temperature
2.10
TA = -30°C
t (ms)
fSW (MHz)
2.05
2.00
TA = +85°C
TA = +25°C
1.95
1.90
2.5
3.0
3.5
4.0
4.5
5.0
5.5
1k
950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100
50
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
FTO (#)
VIN (V)
Figure 23. Frequency vs Input Voltage
Figure 24. Flash Timeout Time vs Flash Timeout Code
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Typical Characteristics (continued)
Unless otherwise specified: TA = 25°C; VIN = 3.6 V; CIN1= 10 µF, CIN2= 0.1 µF, COUT = 11 µF; L = 2.2 µH.
IIN
(500 mA/DIV)
IIN
(500 mA/DIV.)
ILED
(200 mA/DIV)
ILED
(200 mA/DIV)
VOUT
(2V/DIV)
VLED
(2V/DIV)
VOUT
(2V/DIV)
VLED
(2V/DIV)
Time
(800 Ps/DIV)
Time
(100 Ps/DIV)
Two LEDs
I2C Mode
Two LEDs
I2C Mode
Figure 26. Ramp-Down
Figure 25. Start-Up
IIN
(1A/DIV)
VOUT
(5V/DIV)
VLED
(5V/DIV)
IIN
(200 mA/DIV)
ILED
(100 mA/DIV)
ILED
(100 mA/DIV)
Time
(100 Ps/DIV)
Two LEDs
I2C Mode
Time
(200 Ps/DIV)
Two LEDs
Figure 27. Ramp-Down (Zoom)
Figure 28. Start-up
IIN
(1A/DIV)
IIN
(500 mA/DIV)
VOUT
(5V/DIV)
VOUT
(5V/DIV)
VLED
(5V/DIV)
VLED
(5V/DIV)
ILED
(100 mA/DIV)
ILED
(20 mA/DIV)
Time
(200 Ps/DIV)
Two LEDs
Simple Mode
Time
(80 Ps/DIV)
Two LEDs
Figure 29. Ramp-Down
12
Simple Mode
Torch
Figure 30. Diode Detect
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Typical Characteristics (continued)
Unless otherwise specified: TA = 25°C; VIN = 3.6 V; CIN1= 10 µF, CIN2= 0.1 µF, COUT = 11 µF; L = 2.2 µH.
IIN
(500 mA/DIV)
IIN
(500 mA/DIV)
VOUT
(2V/DIV)
VLED
(5V/DIV)
VOUT
(2V/DIV)
VLED
(2V/DIV)
ILED
(50 mA/DIV)
Time
(400 Ps/DIV)
Time
(1 ms/DIV)
Figure 31. Overvoltage Protection Fault (OVP)
Figure 32. VOUT Short to GND Fault
IIN
(500 mA/DIV)
VLED
(200 mA/DIV)
ILED
(200 mA/DIV)
VOUT
(2V/DIV)
VOUT
(2V/DIV)
VLED
(2V/DIV)
IIN
(200 mA/DIV)
Time
(80 Ps/DIV)
Time
(1 ms/DIV)
Figure 33. VLED Short to GND Fault
VIN
(2V/DIV)
Figure 34. Broken Inductor Fault
VTORCH
(1V/DIV)
VOUT
(5V/DIV)
VLED
(5V/DIV)
ILED
(20 mA/DIV)
ILED
(50 mA/DIV)
Time
(10 ms/DIV)
Time
(400 ms/DIV)
Figure 35. Undervoltage Lockout (UVLO)
Figure 36. Torch Deglitching Time
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Typical Characteristics (continued)
Unless otherwise specified: TA = 25°C; VIN = 3.6 V; CIN1= 10 µF, CIN2= 0.1 µF, COUT = 11 µF; L = 2.2 µH.
VSTROBE
(1V/DIV)
VSTROBE
(1V/DIV)
ILED
(100 mA/DIV)
ILED
(100 mA/DIV)
Time
(100 ms/DIV)
Time
(100 ms/DIV)
Figure 37. Edge Sensitive Strobe
Figure 38. Level Sensitive Strobe With Timeout
VSTROBE
(1V/DIV)
ILED
(100 mA/DIV)
Time
(100 ms/DIV)
Figure 39. Level Sensitive Strobe Without Timeout
14
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7 Detailed Description
7.1 Overview
The LM3555 is a high-power white-LED flash driver capable of delivering up to 500 mA of LED current into a
single LED, or up to 400 mA into two series LEDs. The device incorporates a 2-MHz constant frequency,
synchronous, current mode PWM boost converter, and a single high-side current source to regulate the LED
current over the 2.5 V to 5.5 V input voltage range. Dual control interfaces (simple ENABLE control or I2C) and
diode detection (single LED or two LEDs in series) make the LM3555 highly adaptable to a large variety of
designs.
7.2 Functional Block Diagram
TORCH
LED
Open/Short
Detect
STROBE
I2C/EN
SCL/EN1
I2C INTERFACE/
CONTROL LOGIC/
REGISTERS
FLASH CTRL
Current
Control
TIME-OUT CTRL
SDA/EN2
VREF
gm
VIN
VLED
TORCH CTRL
RC
0.3 V
-
CC
+
VOUT
SW
Driver
OVP/Short
Detect
IND
SW
PGND
SW
Driver
SWITCH
CONTROLLER
SGND
THERMAL
SHUTDOWN
OSC
2 MHz
RAMP
CURRENT
LIMT
gm
LM3555
¦
IC
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7.3 Feature Description
7.3.1 Synchronous Boost Converter
The LM3555 operates in two modes: LED boost mode or LED pass mode. When the input voltage is above the
LED voltage plus current source headroom voltage the device turns the PFET on continuously (pass mode). In
pass mode the difference between (VIN – ILED × RON_P) and the voltage across the LEDs is dropped across the
current source. When the output voltage (VOUT) is greater than the input voltage (VIN) minus approximately
200 mV, the PWM converter switches and maintains at least 300 mV across the current source (LED boost
mode). This minimum headroom voltage ensures that the current sinks remain in regulation.
Once the LM3555 transitions from pass mode to boost mode, the device does not return to pass mode until the
device is disabled and re-enabled. At this point, the converter re-evaluates the conditions and enter the
appropriate mode.
7.3.2 High-Side Current Source
The high-side current source of the LM3555 is capable of driving one or two LEDs in series. Depending on the
configuration, the LM3555 automatically sets default diode current levels and diode current limits. For a single
LED, the flash current range is 200 mA to 500 mA in 20-mA steps with a default current equal to 500 mA. For
two LEDs in series, the flash current range is 200 mA to 400 mA in 20-mA steps with a default current equal to
320 mA.
Additionally, the high-side current source is capable of supporting assist/torch current levels (continuous current)
between 60 mA and 160 mA in 20-mA levels.
7.3.3 I2C/EN Pin
The I2C/EN pin on the LM3555 changes the control interface depending on its state. To use the LM3555 in the
simple control mode, the I2C/EN pin must be tied low. To use the LM3555 in I2C control mode, the I2C/EN pin
must be tied high. Toggling this pin between simple control mode and I2C control mode is not recommended.
7.3.4 SDA/EN2 and SCL/EN1 Pins
Depending on the state of the I2C/EN pin, the SDA/EN2 and SCL/EN1 pins function in different ways. If the
I2C/EN pin is equal to a 1, the SDA/EN2 pin functions as an I2C SDA (data) pin, and the SCL/EN1 pin functions
as an I2C SCL (clock) pin. If the I2C/EN pin is equal to a 0, the SDA/EN2 pin functions as the simple control pin
EN2, and the SCL/EN1 pin functions as the simple control pin EN1.
When using the simple control mode, the flash, torch, and indicator modes can be enabled. In simple control
mode, internal pulldown resistors on the SDA/EN2 and SCL/EN1 pins become active. In I2C control mode, these
pulldowns become disabled.
7.3.5 STROBE Pin
The STROBE pin of the LM3555 provides an external method for initiating a flash event. In most cases, the
STROBE pin is connected to an imaging module so that the image capture and flash event are synchronized.
The STROBE pin is only functional when the LM3555 is placed into I2C control mode (I2C/EN = 1) and the output
on (OEN in 0x04) and strobe signal Mode (SEN in 0x04) bits are set (1). The STROBE pin can be configured to
be an edge sensitive or level sensitive input by setting the strobe signal usage bit (SSU in 0x04. 1 = Level, 0 =
Edge). In edge sensitive mode, a rising edge transition (0 to 1) starts the flash event, and the internal flash timer
terminates the event. In level sensitive mode, a rising edge transition (0 to 1) starts the flash event and a falling
edge transition (1 to 0) or the internal flash timer, whichever occurs first, terminates the event. In I2C mode, there
is an internal pulldown resistor that becomes enabled on the STROBE pin.
In simple control mode, the STROBE pin functions as a output when a pullup resistor is connected, alerting the
user to the number of flash LEDs present in the system. If the STROBE pin is outputting a 1, two LEDs are
present, whereas a 0 indicates a single LED is present.
16
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Feature Description (continued)
7.3.6 TORCH Pin
The TORCH pin of the LM3555, depending on the state and configuration, allows the user to enable torch/assist
mode without having to write the command through the I2C bus or through toggling the EN1 and EN2 pins. In
simple mode, the LM3555 drives 60 mA of LED current if two series LEDs are present and 80 mA is one LED is
present. In I2C mode, the external torch mode bit (TEN in register 0x04) must be set to a 1 to allow an external
torch (default value = 1). In I2C mode, the torch mode current is equal to the Assist mode current level stored in
register 0x03. The TORCH pin has an internal pulldown resistor enabled in both simple mode and I2C mode.
7.3.7 Indicator LED Pin (IND)
The indicator LED current source pin (IND) is able to drive a single red indicator LED when the anode is
connected to the LM3555 and the cathode is connected to ground. In simple logic mode, the default indicator
current is 2.5 mA, and in I2C mode, the indicator LED current can be adjusted to 2.5 mA, 5 mA, 7.5 mA, or 10
mA.
7.3.8 Internal Diode Detection
During the start-up sequence of the LM3555 an internal voltage comparator on the VLED pin monitors the
forward voltage of the LED or LEDs. This measurement occurs when the ramp-up current reaches 80 mA. If, at
this time, the diode voltage exceeds the user-selectable diode detect threshold (Register 0x02 bits VO1 and
VO0), the LM3555 assumes two series LEDs are present and limits the maximum flash current to 400 mA. The
four adjustable levels are; 00 = 4.35 V, 01 = 4.65 V, 10 = 4.05 V and 11 = 4.95 V. This detection feature can be
disabled by setting the diode detect enable bit (DEN) in the Current Set Register (address 0x03) to a 0. The DEN
bit is set to a 1 (enabled) by default.
In all cases during start-up, the diode current first ramps to 80 mA and then proceeds to the target current. If the
torch/assist current is set to 60 mA, the LM3555 first reaches 80 mA and then drop to 60 mA.
The number of LEDs present in the system is recorded in a read-only diode number (DN) bit of the fault register
(address 0x05). In simple mode, the number of LEDs present are output on the STROBE pin (0 = 1 LED, 1 = 2
LEDs).
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Feature Description (continued)
7.3.9 Fault Protections
The LM3555 has a number of fault protection mechanisms designed to not only protect the LM3555 device itself,
but also the rest of the system. Active faults protections include:
• Overvoltage protection (VOUT)
• Short-Circuit protection (VOUT and VLED)
• Overtemperature protection
• Flash timeout
• Indicator LED protection (open and short)
• Broken inductor protection
In the event that any of these faults occur, the LM3555 sets a flag in the Fault Register (Address 0x05) and
places the device into standby or shutdown. In simple control mode, normal operation cannot resume until the
fault has been fixed and until EN1 and EN2 are driven low 0. In I2C control mode, normal operation cannot
resume until the fault has be fixed and until an I2C read of the faults register (0x05) has completed. The act of
reading the fault register clears the fault bits.
7.3.9.1 Output Overvoltage Protection (OVP)
An OVP fault is triggered when the output voltage of the LM3555 reaches a value greater than 9.5 V (typical).
The OVP condition is cleared when the output voltage (VOUT) is able to operate below 9.5 V. An output capacitor
or an LED that has become an open circuit can cause an OVP event to occur. This fault is reported to the OVP
fault bit in the Fault Register (bit7 in address 0x05).
7.3.9.2 Output and LED Short-Circuit Protection (SCP)
An SCP fault is triggered when the output voltage (VOUT) and/or the VLED pin does not reach 0.8 V in 0.5 ms.
The short circuit condition is cleared when the output (VOUT) is allowed to reach its steady state target and
when the LED voltage rises above 0.8 V. A shorted output capacitor or a shorted LED could cause this fault to
occur. This fault is reported to the SC fault bit in the Fault Register (bit6 in address 0x05).
7.3.9.3 Overtemperature Protection (OTP)
An OTP fault is triggered when the diode junction temperature of the LM3555 reaches an internal temperature of
around 150°C. The OTP condition is cleared when the junction temperature falls below 140°C. A printed circuit
board (PCB) with poor thermal dissipation properties and very high ambient temperatures (greater that 85°C)
could cause this fault to occur. Refer to AN-1112 DSBGA Wafer Level Chip Scale Package (SNVA009) for more
information regarding proper PCB layout. This fault is reported to the OTP fault bit in the Fault Register (bit5 in
address 0x05).
7.3.9.4 Flash Timeout (FTP)
An FTP fault is triggered any time the flash pulse duration reaches the flash timeout duration. In I2C control
mode, the FTP fault is triggered whenever a flash is initiated through the Control Register (OEN and OM1/OM0
bits) or through an edge-sensitive strobe event. A FTP fault could occur in simple control Mode if the controller
tied to EN1 and EN2 pins cannot toggle the pins low at the desired pulse rate. This same condition could occur
with a level-sensitive strobe event controlled by a camera module. This fault is reported to the TO fault bit in the
Fault Register (bit4 in address 0x05). A FTP fault is the only reported fault that does not need to be cleared
before any additional LED event can occur.
7.3.9.5 Indicator Fault (IF)
An IF fault is triggered when the voltage on the IND pin is greater than 2.571 V or less than 0.842 V. This fault
indicates that there is either an open or a short present on the IND pin. The short-circuit condition is cleared
when the IND pin is allowed to operate between 0.842 V and 2.571 V. A shorted or open indicator LED could
cause this fault to occur. This fault is reported to the IF fault bit in the Fault Register (bit2 in address 0x05).
18
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Feature Description (continued)
7.3.9.6 Broken Inductor Fault (IP)
An IP fault is triggered when the LM3555 detects that the inductance of the inductor has dropped below an
acceptable value. This fault indicates that the inductor has been damaged. An inductor that has had its ferrite
material damaged could cause this fault to occur. This fault is reported to the IP fault bit in the Fault Register
(bit1 in address 0x05).
7.3.10 Undervoltage Lockout (UVLO)
The LM3555 has a UVLO feature that disables the operation of the device in the event that the input voltage falls
below 2.4 V (typical). In simple control mode, the input voltage must increase to at least 2.47 V (typical), and the
EN1 and EN2 pins must be toggled low (0) before normal operation can resume.
In I2C control mode, the output enable bit in the Control Register (Address 0x04) is set to a 0 in the event of a
UVLO occurrence. The input voltage must rise to at least 2.47 V before the LM3555 becomes fully functional
again.
A UVLO event does not disturb the state of the other registers of the LM3555.
7.3.11 Power-On Reset (POR)
A POR circuit is present on the LM3555 for use in I2C control mode. The POR circuit ensures that the device
starts in a known OFF state and that the registers used in the I2C control interface are initialized to the proper
start-up values once the input voltage reaches a voltage greater than 1.8 V (typical). An input voltage lower than
1.8 V not only places the device into UVLO, but also clears all of the LM3555 registers.
7.4 Device Functional Modes
7.4.1 Single LED Operation
In single LED operation, the LED flash current is allowed to reach the maximum level of 500 mA. By default, the
assist/torch current is set to 80 mA, and the flash current is set to 500 mA.
For input voltages that are higher than the LED forward voltage, the LM3555 operates in a pass mode. As VIN
drops, the LM3555 first transitions from pass mode to the minimum duty-cycle boost mode. In this mode, the
output voltage (VOUT) increases to a level higher than needed to maintain current regulation through the current
source. If VIN continues to decrease, the LM3555 transitions again, this time from minimum duty-cycle boost
mode to standard boost mode. Standard boost mode adjusts the converters duty cycle to maintain 300 mV
across the current source of the device.
Once the LM3555 transitions from pass mode to either boost mode, the device stays in one of those boost
modes until the device is disabled or timed-out and then restarted.
7.4.2 Dual LED Operation
In dual LED operation, the LED flash current is allowed to reach a maximum level of 400 mA. By default, the
assist/torch current is set to 60 mA, and the flash current is set to 320 mA.
During dual LED operation, the output voltage is always greater than the input voltage (assuming standard white
flash LEDs are used), forcing the LM3555 to be in boost mode over the entire input voltage range.
7.4.3 Torch or Assist (Continuous Current) Operation
There are two different continuous current modes on the LM3555: torch and assist.
Torch mode is enabled through the use of the dedicated TORCH pin using both simple and I2C modes (1 =
Torch, 0 = Standby (I2C mode) or shutdown (simple mode). In I2C control mode, the TORCH pin functionality can
be enabled and disabled through by setting the value of the TEN bit in the Control Register (Address 0x04). TEN
= 1 allows an external torch while TEN = 0 does not.
Assist mode is enabled in simple control mode by driving EN1 low (0) and by driving EN2 high (1). In I2C control
mode, assist mode is enabled by setting the output mode bits (OM1 and OM0) to 10 and setting the output
enable bit (OEN) to a 1 in the Control Register (0x04). Assist mode remains active in I2C mode until the OEM bit
is set to 0 or until a flash event occurs.
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Device Functional Modes (continued)
The LM3555 can drive one or two LEDs at continuous current levels ranging from 60 mA to 160 mA in 20-mA
steps. In simple control mode, the torch and assist current levels are equal to 60 mA for two LEDs or 80 mA for a
single LED. In I2C mode, the current is set in the Current Set Register (Address 0x30, AC2-AC0 bits).
7.4.4 Flash (Pulsed Current) Operation
A flash event using the LM3555 can be initiated though the dedicated control interface in both simple and I2C
modes, and through the use of the STROBE pin in I2C mode.
By driving both EN1 and EN2 high (1) in simple mode, the device enters flash mode and remains there until the
control pins are driven low (0), or a timeout event occurs. In simple mode, the flash current is equal to 500 mA
when driving a single LED and 320 mA when two LEDs are present. The default time-out duration is 850 ms.
When placed into I2C Control mode, a flash event is initiated when the output mode bits (OM1 and OM0) are set
to 11, and the output enable bit (OEN) is set to a 1 in the Control Register (0x04). In I2C mode, the flash event
remains active as long as the OEN bit is set to a 1 and terminates upon a timeout event. The safety timer
duration can be set in 50 ms intervals ranging from 100 ms to 850 ms by writing the desired value to the FT3FT0 bits in the Indicator and Timer Register (Address 0x02).
The STROBE pin provides added system flexibility because it allows an additional external device (camera
module, GPU, and so forth) to trigger a flash event. To initiate a strobe event in I2C control mode, the strobe
signal mode (SEN) bit and the output enable (OEN) bits in the Control Register (Address 0x04) must first be set
to 1's.
Following the setting of the SEN and OEN bits, the user must chose to have an edge-sensitive or level-sensitive
strobe event. Writing a 1 to the strobe signal usage (SSU) bit in the Control Register (Address 0x04), the
LM3555 is configured to be level sensitive, while writing a 0 configures the device to be edge sensitive. In both
cases, the strobe flash event is started upon the STROBE pin being driven high.
In an edge-sensitive event, the flash duration stays active until the flash duration timer lapses regardless of the
state of the STROBE pin. If a level-sensitive strobe is used, the flash event remains active as long as the
STROBE pin is held high and as long as the flash duration time has not lapsed.
In I2C control mode, the end of a flash event, whether initiated through the Control Register or STROBE pin,
forces the OEN bit to a 0 and places the LM3555 back into the standby state.
7.4.5 Indicator Operation
Indicator mode is enabled in simple control mode by driving EN1 high (1) and by driving EN2 high (0). In I2C
control mode, Indicator mode is enabled by setting the output mode bits (OM1 and OM0) to 01 and setting the
Output Enable bit (OEN) to a 1 in the Control Register (0x04). Indicator mode remains active in I2C mode until
the OEM bit is set to 0 or until a torch or flash event occurs.
In simple control mode, the indicator LED current is fixed to 2.5 mA, while in I2C control mode, the indicator
current is adjustable to 2.5 mA, 5 mA, 7.5 mA, or 10 mA by changing the values of the IC1 and IC0 bits in the
Indicator and Timer Register (Address 0x02).
7.4.6 Simple Control State Diagram
Flash
Assist Light
Shutdown
Red
Indicator
20
External
Torch
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Device Functional Modes (continued)
Table 1. Simple Mode Truth Table (1)
(1)
EN1
EN2
TORCH
MODE
0
0
0
shutdown
0
0
1
external torch
0
1
X
assist light
1
0
X
indicator
1
1
X
flash
I2C/EN = 0
Internal
Flash
Strobe Flash
Edge
Strobe Flash
Level
Shutdown
Standby
Output On
External
Torch
Red
Indicator
Assist Light
External
Torch
Figure 40. I2C Control State Diagram
Table 2. I2C Mode Truth Table (1)
(1)
OEN
OM1
OM0
TEN
SEN
TORCH
STROBE
MODE
0
0
0
0
X
X
X
standby
0
0
0
1
X
0
X
standby
0
0
0
1
X
1
X
external torch
0
0
1
X
X
X
X
atandby
0
1
0
X
X
X
X
atandby
0
1
1
X
X
X
X
atandby
1
0
0
X
X
0
X
atandby
1
0
0
X
X
1
X
external torch
1
0
1
X
X
X
X
indicator
1
1
0
X
X
X
X
assist
1
1
1
X
0
X
X
internal flash
1
1
1
X
1
X
0
atandby
1
1
1
X
1
X
1
strobe flash
I2C/EN = 1, SCL and SDA = X
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7.5 Programming
7.5.1 I2C-Compatible Interface
7.5.1.1 Data Validity
The data on SDA line must be stable during the HIGH period of the clock signal (SCL). In other words, the state
of the data line can only be changed when CLK is LOW.
SCL
SDA
data
change
allowed
data
valid
data
change
allowed
data
valid
data
change
allowed
Figure 41. Data Validity Diagram
A pullup resistor between VIO and SDA must be greater than (VIO – VOL) / 3 mA to meet the VOL requirement on
SDA. Using a larger pullup resistor results in lower switching current with slower edges, while using a smaller
pullup results in higher switching currents with faster edges.
7.5.1.2 Start and Stop Conditions
START and STOP conditions classify the beginning and the end of the I2C session. A START condition is
defined as SDA signal transitioning from HIGH to LOW while SCL line is HIGH. A STOP condition is defined as
the SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master always generates START and
STOP conditions. The I2C bus is considered to be busy after a START condition and free after a STOP condition.
During data transmission, the I2C master can generate repeated START conditions. First START and repeated
START conditions are equivalent, function-wise. The data on SDA line must be stable during the HIGH period of
the clock signal (SCL). In other words, the state of the data line can only be changed when CLK is LOW.
SDA
SCL
S
P
START condition
STOP condition
Figure 42. Start and Stop Conditions
7.5.1.3 Transferring Data
Every byte put on the SDA line must be eight bits long, with the most significant bit (MSB) being transferred first.
Each byte of data has to be followed by an acknowledge bit. The acknowledge related clock pulse is generated
by the master. The master releases the SDA line (HIGH) during the acknowledge clock pulse. The LM3555 pulls
down the SDA line during the 9th clock pulse, signifying an acknowledge. The LM3555 generates an
acknowledge after each byte has been received.
After the START condition, the I2C master sends a chip address. This address is seven bits long followed by an
eighth bit which is a data direction bit (R/W). The LM3555 address is 30h. For the eighth bit, a 0 indicates a
WRITE and a 1 indicates a READ. The second byte selects the register to which the data is written. The third
byte contains data to write to the selected register.
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Programming (continued)
ack from slave
ack from slave
start
msb Chip Address lsb
w
ack
msb Register Add lsb
ack
start
Id = 30h
w
ack
addr = 04h
ack
ack from slave
msb
DATA
lsb
ack
stop
ack
stop
SCL
SDIO
data = 08h
w = write (SDA = 0); ack = acknowledge (SDA pulled down by the slave): id = chip address, 30h for LM3555
Figure 43. Write Cycle
7.5.1.4 I2C-Compatible Chip Address
The chip address for LM3555 is 0110000, or 30hex.
MSB
LSB
ADR6
bit7
ADR5
bit6
ADR4
bit5
ADR3
bit4
ADR2
bit3
ADR1
bit2
ADR0
bit1
0
1
1
0
0
0
0
R/W
bit0
2
I C Slave Address (chip address)
Figure 44. Device Address
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7.6 Register Maps
7.6.1 Internal Registers of LM3555
REGISTER
INTERNAL HEX ADDRESS
POWER ON VALUE
Version Control Register
0x01
0000 1100
Indicator and Timer Register
0x02
0000 1111
Current Set Register
0x03
0110 1001
Control Register
0x04
1011 0100
Fault Register
0x05
0000 1000
7.6.2 Register Definitions
Definition:
RF3 RF2 RF1 RF0 DR3 DR2 DR1 DR0
Default:
0
0
0
0
0110 0110 0110 0110
ARF3–RF0: unused
DR3–DR0: design revision = 1100
Figure 45. Version Control Register, Address: 0x01
Definition:
IC1 IC0 VO1 VO0 FT3 FT2 FT1 FT0
Default:
0
0
0
0
1
1
1
1
IC1–IC0: indicator LED current control bits
VO1-VO0: VREF offset adjustment bits. used for diode detection.
FT3-FT0: software flash timer duration control bits
Figure 46. Indicator and Timer Register, Address: 0x02
Table 3. Indicator Currents
IC1
IC0
INDICATOR LED CURRENT
0
0
2.5 mA
0
1
5 mA
1
0
7.5 mA
1
1
10.0 mA
Table 4. Offset Voltages
VREFVOLTAGE
(OFFSET FROM 4.35 V)
VO1
VO0
0
0
4.35 V (+0 V)
0
1
4.65 V (+0.3 V)
1
0
4.05 V (−0.3 V)
1
1
4.95 V (+0.6 V)
Table 5. Flash Timeout Duration
24
FT3
FT2
FT1
FT0
FLASH TIMEOUT DURATION
0
0
0
0
100 ms
0
0
0
1
150 ms
0
0
1
0
200 ms
0
0
1
1
250 ms
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Table 5. Flash Timeout Duration (continued)
FT3
FT2
FT1
FT0
FLASH TIMEOUT DURATION
0
1
0
0
300 ms
0
1
0
1
350 ms
0
1
1
0
400 ms
0
1
1
1
450 ms
1
0
0
0
500 ms
1
0
0
1
550 ms
1
0
1
0
600 ms
1
0
1
1
650 ms
1
1
0
0
700 ms
1
1
0
1
750 ms
1
1
1
0
800 ms
1
1
1
1
850 ms
Definition: FC3 FC2 FC1 FC0 DEN AC2 AC1 AC0
Default:
0
1
1
0
1
0
0
1
FC3-FC0: flash current control bits
DEN: diode detection enable bit. 1 = en, 0 = disabled. default = 1 (enabled)
AC2-AC0: assist light current control bits
Figure 47. Current Set Register, Address: 0x03
Table 6. Flash Current Levels
FC3
FC2
FC1
FC0
FLASH CURRENT LEVEL
0
0
0
0
200 mA
0
0
0
1
220 mA
0
0
1
0
240 mA
0
0
1
1
260 mA
0
1
0
0
280 mA
0
1
0
1
300 mA
0
1
1
0
320 mA (2 LEDs)
0
1
1
1
340 mA
1
0
0
0
360 mA
1
0
0
1
380 mA
1
0
1
0
400 mA (2 LED maximum)
1
0
1
1
420 mA
1
1
0
0
440 mA
1
1
0
1
460 mA
1
1
1
0
480 mA
1
1
1
1
500 mA (1LED)
Table 7. Assist Light Current Levels
AC2
AC1
AC0
ASSIST CURRENT LEVEL
0
0
0
60 mA
0
0
1
60 mA (2 LEDs)
0
1
0
60 mA
0
1
1
80 mA (1 LED)
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Table 7. Assist Light Current Levels (continued)
AC2
AC1
AC0
ASSIST CURRENT LEVEL
1
0
0
100 mA
1
0
1
120 mA
1
1
0
140 mA
1
1
1
160 mA
Definition: IL1
Default:
1
IL0 SSU TEN OEN SEN OM1 OM0
0
1
1
0
1
0
0
IL1-IL0: peak inductor current limit bits
SSU: strobe signal usage. 0 = edge sensitive, 1 = level sensitive. 1 = default
TEN: external torch mode enable. 0 = not allowed, 1 = allowed. 1 = default
OEN: output enable. 0 = output disabled, 1 = output enabled. 0 = default
SEN: strobe signal mode. 0 = disabled, 1 = enabled. 1 = default
OM1-OM0: output mode select bits
Figure 48. Control Register, Address: 0x04
Table 8. Peak Inductor Current Limit Levels
IL1
IL0
PEAK INDUCTOR CURRENT LIMIT
0
0
1.25 A
0
1
1.5 A
1
0
1.75 A
1
1
2A
Table 9. Output Modes
OM1
OM0
OUTPUT MODE
0
0
external torch
0
1
indicator
1
0
assist light
1
1
flash
Definition: OVP SC OTP TO DN
Default:
0
0
0
0
X
IF
IP RFU
0
0
0
OVP: overvoltage protection fault. 1 = fault, 0 = no fault
SC: short-circuit fault: 1 = Fault, 0 = no fault
OTP: overtemperature protection fault. 1 = fault, 0 = no fault
TO: flash timeout fault. 1 = fault, 0 = no fault
DN: number of LEDs. 1 = 2 LEDs, 0 = 1 LED. (This bit is R/W). 1 = fault, 0 = no fault
IF: indicator LED fault. 1 = fault, 0 = no fault
IP: inductor peak current limit fault (broken inductor fault). 1 = fault, 0 = no fault
RFU: not used
Figure 49. Fault and Info Register, Address: 0x05
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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 LM3555 is a white-LED driver for LED camera flash applications. The dual high-side current sources allow
for grounded cathode LEDs. The LM3555 can adaptively scale the maximum flash level delivered to the LEDs
based upon the flash configuration, whether it be a single LED or two LEDs in series.
8.2 Typical Application
2.2 µH
CIN
10 µF
SW
VIN
VOUT
+
VBAT
COUT
10 µF
STROBE
TORCH
I2C/EN
VLED
LM3555
SCL/EN1
SDA/EN2
PGND
SGND
IND
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Figure 50. LM3555 Typical Application
8.2.1 Design Requirements
For typical white-LED driver applications, use the parameters listed in Table 10.
Table 10. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range
2.5 V to 5.5 V
Number of LEDs
1 or 2 LEDs in Series
Output current range
60 mA to 500mA
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8.2.2 Detailed Design Procedure
8.2.2.1 Inductor Current Limit
To prevent damage to the inductor of the LM3555 and to limit the power drawn by the LM3555 during a flash
event, an inductor current limit circuit is present. The LM3555 monitors the current through the inductor during
the charge phase of the boost cycle. In the event that the inductor current reaches the current limit, the NFET of
the converter terminates the charge phase for that cycle. The process repeats itself until the flash event has
ended or until the input voltage increases to the point where the peak current is no longer reached. Hitting the
peak inductor current limit does not disable the part. It does, however, limit the output power delivery to the
LEDs.
In simple control mode, the peak inductor current limit is set to 1.75 A. In I2C control mode, the inductor current
limit can be set to 1.25 A, 1.5 A, 1.75 A, and 2 A depending on the values of the IL1 and IL0 bits in the Control
Register (address 0x04). The peak inductor current limit value can be used to help size the inductor to the
appropriate saturation current level. For more information on inductor sizing, please refer to the Inductor
Selection.
8.2.2.2 Inductor Selection
The LM3555 is designed to use a 2.2-µH inductor. When the device is boosting (VOUT > VIN) the inductor is one
of the biggest sources 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 LM3555. 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 LM3555 (1.25 A, 1.5 A, 1.75 A, or 2 A) is greater than IPEAK. 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
(1)
Table 11. Recommended Inductors
MANUFACTURER
PART NUMBER
L / ISAT
Toko
FDSE312-2R2M
2.2 µH / 2.3 A
Coilcraft
LPS4012-222ML
2.2 µH / 2.3 A
TDK
VLF4014ST-2R2M1R9
2.2 µH / 2 A
8.2.2.3 Capacitor Selection
The LM3555 requires 2 external capacitors for proper operation (TI recommends CIN = 10 µF (4.7 µF minimum)
and COUT = 10 µF ). TI also recommends placing an additional 0.1-µF input capacitor placed right next to the VIN
pin. Surface-mount multi-layer ceramic capacitors are recommended. These capacitors are small, inexpensive
and have very low equivalent series resistance (ESR < 20 mΩ typical). Tantalum capacitors, OS-CON
capacitors, and aluminum electrolytic capacitors are not recommended for use with the LM3555 due to their high
ESR, as compared to ceramic capacitors.
For most applications, ceramic capacitors with X7R or X5R temperature characteristic are preferred for use with
the LM3555. These capacitors have tight capacitance tolerance (as good as ±10%) and hold their value over
temperature (X7R: ±15% over −55°C to +125°C; X5R: ±15% over −55°C to 85°C).
Capacitors with Y5V or Z5U temperature characteristic are generally not recommended for use with the LM3555.
Capacitors with these temperature characteristics typically have wide capacitance tolerance (80%, −20%) and
vary significantly over temperature (Y5V: 22%, –82% over −30°C to +85°C range; Z5U: 22%, –56% over 10°C to
85°C range). Under some conditions, a nominal 1-µF Y5V or Z5U capacitor could have a capacitance of only 0.1
µF. Such detrimental deviation is likely to cause Y5V and Z5U capacitors to fail to meet the minimum
capacitance requirements of the LM3555.
The recommended voltage rating for the input capacitor is 10 V (minimum = 6.3 V). The recommended output
capacitor voltage rating is 16 V (minimum = 10 V). The recommended value takes into account the DC bias
capacitance losses, while the minimum rating takes into account the OVP trip levels.
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8.2.3 Application Curves
100
100
TA = -30°C
90
80
80
äLED (%)
äLED (%)
TA = -30°C
90
TA = +85°C
TA = +25°C
70
TA = +85°C
70
TA = +25°C
60
60
VLED (@ 320 mA) = 6.75V (2 LEDs)
50
2.5
3.0
3.5
4.0
4.5
5.0
VLED (@ 400 mA) = 6.9V (2 LEDs)
50
2.5
5.5
3.0
3.5
4.0
VIN (V)
5.0
5.5
VIN (V)
Two Series LEDs at 320 mA
Two Series LEDs at 400 mA
Figure 51. LED Efficiency vs Input Voltage
Figure 52. LED Efficiency vs Input Voltage
100
100
TA = -30°C
90
90
TA = -30°C
80
80
äLED (%)
äLED (%)
4.5
70
TA = +85°C
60
TA = +25°C
70
TA = +85°C
TA = +25°C
60
50
50
VLED (V) = 6.0V (2 LEDs)
40
2.5
3.0
3.5
4.0
4.5
5.0
40
2.5
5.5
VLED (V) = 6.1V (2 LEDs)
3.0
3.5
VIN (V)
4.0
4.5
5.0
5.5
VIN (V)
Two LEDs at 60 mA
Two LEDs at 80 mA
Figure 53. LED Efficiency vs Input Voltage
Figure 54. LED Efficiency vs Input Voltage
100
100
VLED (@ 500 mA) = 3.6V
TA = -30°C
90
90
TA = +25°C
äLED (%)
äLED (%)
80
80
70
TA = +85°C
TA = -30°C
70
60
TA = +25°C
60
50
TA = +85°C
50
2.5
3.0
3.5
4.0
4.5
5.0
40
2.5
5.5
3.0
3.5
VLED (V) = 3.0V
4.0
4.5
5.0
5.5
VIN (V)
VIN (V)
One LED at 60 mA
One LED at 500 mA
Figure 55. LED Efficiency vs Input Voltage
Figure 56. LED Efficiency vs Input Voltage
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100
90
TA = +25°C
80
äLED (%)
TA = -30°C
70
60
50
TA = +85°C
VLED (V) = 3.0V
40
2.5
3.0
3.5
4.0
4.5
5.0
5.5
VIN (V)
One LED at 80 mA
Figure 57. LED Efficiency vs Input Voltage
9 Power Supply Recommendations
The LM3555 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 DSBGA is a chip-scale package with good thermal properties. For more detailed instructions on handling
and mounting DSBGA packages, refer to AN-1112 DSBGA Wafer Level Chip Scale Package (SNVA009).
The high switching frequencies and large peak currents make the PCB layout a critical part of the design. The
proceeding steps must be followed to ensure stable operation and proper current source regulation.
1. Connect the inductor as close to the SW pin as possible. This reduces the inductance and resistance of the
switching node which minimizes ringing and excess voltage drops.
2. Connect the return terminals of the input capacitor and the output capacitor as close to the two ground pins
(PGND and SGND) as possible and through low impedance traces.
3. Bypass VIN with a 10-µF ceramic capacitor and an additional 0.1-µF ceramic capacitor. Connect the positive
terminal of this capacitor as close to VIN as possible.
4. Connect COUT as close to the VOUT pin as possible. This reduces the inductance and resistance of the output
bypass node which minimizes ringing and voltage drops. This improves efficiency and decreases the noise
injected into the current sources.
10.2 Layout Example
CIN1
4.45 mm
CIN2
L1
COUT
LM3555
7.0 mm
Figure 58. LM3555 Layout
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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:
AN-1112 DSBGA Wafer Level Chip Scale Package (SNVA009)
11.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.4 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.5 Electrostatic Discharge Caution
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)
LM3555TLE/NOPB
ACTIVE
DSBGA
YZR
12
250
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-30 to 85
3555
LM3555TLX/NOPB
ACTIVE
DSBGA
YZR
12
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-30 to 85
3555
(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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