Dual LED Flash Driver with
I2C-Compatible Interface
ADP1655
FEATURES
FUNCTIONAL BLOCK DIAGRAM
INPUT VOLTAGE = 2.5V TO 5.5V
2.2µH
STROBE VIN
10µF
SW
TORCH
VOUT
10µF
ADP1655
SCL/EN1
LED_OUT
SDA/EN2
TX_MASK
I2C/EN SGND PGND
08028-001
Figure 1.
Li-ION +
C1
L1
3mm
PGND
Li-ION +
INDUCTOR
DIGITAL
INPUT/
OUTPUT
C2
LED
ANODE
6.5mm
08028-002
Ultracompact solution
Small 2 mm × 1.5 mm 12-ball WLCSP package
Tiny, low profile 2.2 μH power inductor
LED current source for local LED grounding and low EMI
Synchronous 2 MHz PWM boost convertor, no external diode
High efficiency: 88% peak
Reduces high levels of input battery current during flash
Limits battery current drain in torch mode
I2C programmable
Currents up to 400 mA in flash mode for two LEDs
Currents up to 500 mA in flash mode for one LED with
5% accuracy
Currents up to 160 mA in torch mode with 10% accuracy
Peak inductor current limit
Flash timer
Control
I2C-compatible control registers
External STROBE pin
External direct TORCH pin
TX_MASK input to prevent high input battery current levels
Safety
Thermal overload protection
Flash timeout
Inductor fault detection
Output overvoltage
Short circuit protection
Soft start reduces inrush input current
Figure 2. PCB Layout
APPLICATIONS
Camera-enabled cellular phones and smart phones
Digital still cameras, camcorders, and PDAs
GENERAL DESCRIPTION
The ADP1655 is a very compact, highly efficient, dual white
LED flash driver for high resolution camera phones, which
improves picture and video quality in low light environments.
The device integrates a 2 MHz synchronous inductive boost
convertor, an I2C-compatible interface and a 500 mA current
source. The high switching frequency enables the use of a tiny,
low profile 2.2 μH power inductor, and the current source
permits LED cathode grounding for thermally enhanced,
low EMI and compact layouts.
The efficiency is high over the entire battery voltage range to
maximize the input power to LED power conversion and
minimize battery current draw during flash events. In addition,
a Tx-mask input permits the flash LED current to reduce quickly
and, therefore, the battery current reduces quickly, during a
GSM power amplifier current burst.
The I2C-compatible interface enables the programmability
of timers, currents, and status bit readback for operation
monitoring and safety control.
The ADP1655 comes in a compact 12-ball 0.5 mm pitch
WLCSP package and is specified over the full −40°C to
+125°C junction temperature range.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2009 Analog Devices, Inc. All rights reserved.
ADP1655
TABLE OF CONTENTS
Features .............................................................................................. 1
2-Bit Logic Interface Mode (I2C/EN = 0) ............................... 13
Applications ....................................................................................... 1
I2C Interface Mode (I2C/EN = 1)............................................. 13
Functional Block Diagram .............................................................. 1
State Transitions ......................................................................... 15
2
General Description ......................................................................... 1
I C Register Map ............................................................................. 16
Revision History ............................................................................... 2
Safety Features................................................................................. 19
Specifications..................................................................................... 3
Overvoltage Fault ....................................................................... 19
Recommended Specifications: Input and Output Capacitance
and Inductance ............................................................................. 4
Output Capacitor Fault .............................................................. 19
I2C-Compatible Interface Timing Specifications ..................... 5
Overtemperature Fault .............................................................. 19
Absolute Maximum Ratings............................................................ 6
Short-Circuit Fault ..................................................................... 19
Thermal Data ................................................................................ 6
Current Limit .............................................................................. 19
Thermal Resistance ...................................................................... 6
Amount of LED Detection ........................................................ 19
ESD Caution .................................................................................. 6
Input Undervoltage .................................................................... 19
Pin Configuration and Function Descriptions ............................. 7
Applications Information .............................................................. 20
Typical Performance Characteristics ............................................. 8
External Component Selection ................................................ 20
Theory of Operation ...................................................................... 12
PCB Layout...................................................................................... 22
White LED Driver ...................................................................... 12
Outline Dimensions ....................................................................... 23
Assist Light and Torch Modes .................................................. 12
Ordering Guide .......................................................................... 23
Timeout Fault.............................................................................. 19
REVISION HISTORY
5/09—Revison 0: Initial Version
Rev. 0 | Page 2 of 24
ADP1655
SPECIFICATIONS
VIN = 3.6 V, TJ = −40°C to +125°C for minimum/maximum specifications and TA = 25°C for typical specifications, unless
otherwise noted.
Table 1.
Parameter 1
SUPPLY
Input Voltage Range
Undervoltage Lockout Threshold
Hysteresis
Shutdown Current
Standby Current
I2C/EN = SCL/EN1 = SDA/EN2 = 1.8 V
Operating Quiescent Current
SW Switch Leakage
INPUTS
Input Logic Low Voltage
Input Logic High Voltage
TORCH, STROBE, TX_MASK Pull-Down
SCL/EN1, SDA/EN2 Pull-Down
TORCH Glitch Filtering Delay
LED DRIVER
LED Current
Assist Light, Torch
Flash
LED Current Accuracy
LED Current Source Headroom 2
Conditions
Min
VIN falling
2.7
2.3
50
TJ = −40°C to +85°C, current into VIN pin, VIN = 2.7 V to 4.5 V
TJ = −40°C to +85°C, current into VIN pin, VIN = 2.7 V to 4.5 V
Torch mode, two LEDs, LED current = 40 mA
TJ = −40°C to +85°C
Typ
Max
Unit
2.4
100
0.3
3
5.5
2.5
150
1
10
V
V
mV
μA
μA
1
mA
μA
5.3
0.54
1.26
I2C/EN = 0 V
From TORCH rising edge to device start
I2C/EN = 0, one LED
I2C/EN = 0, two LEDs
I2C/EN = 1, assist light value setting = 0 (000 binary)
I2C/EN = 1, assist light value setting = 7 (111 binary)
I2C/EN = 0, one LED
I2C/EN = 0, two LEDs
I2C/EN = 1, flash value setting = 0 (0000 binary)
I2C/EN = 1, one LED, flash value setting = 15 (1111 binary)
I2C/EN = 1, two LEDs, flash value setting = 10 to 15 (1010 to
1111 binary)
ILED = 320 mA to 500 mA
ILED = 60 mA to 320 mA
ILED = 20 mA to 60 mA
Flash typical, 400 mA LED current
Torch 160 mA
LED_OUT Ramp-Up Time
LED_OUT Ramp-Down Time
Maximum Timeout For Flash
Timer Accuracy
SWITCHING REGULATOR
Switching Frequency
Minimum Duty Cycle
N-FET Resistance
P-FET Resistance
6.3
350
350
9
11.7
80
40
20
160
500
320
200
500
400
−5
−5
−5
mA
mA
mA
mA
mA
mA
mA
mA
mA
+5
+10
+20
%
%
%
mV
1
0.5
ms
ms
ms
%
290
190
850
−7.5
1.85
Rev. 0 | Page 3 of 24
+7.5
2
9.0
135
290
V
V
kΩ
kΩ
ms
2.15
MHz
%
mΩ
mΩ
ADP1655
Parameter 1
SAFETY FEATURES
Thermal Shutdown Threshold
TJ Rising
TJ Falling
Overvoltage Threshold
Coil Peak Current Limit
Conditions
Min
9.0
1.13
1.35
1.58
1.8
Peak current value setting = 0 (00 binary)
Peak current value setting = 1 (01 binary)
Peak current value setting = 2 (10 binary)
Peak current value setting = 3 (11 binary)
LED_OUT Short-Circuit Detection
Comparator Reference Voltage
LED Counting Comparator
Threshold Voltage
LED value setting = 0 (00 binary)
LED value setting = 1 (01 binary)
LED value setting = 2 (10 binary)
LED value setting = 3 (11 binary)
1
2
Typ
150
140
9.5
1.25
1.5
1.75
2.0
1.2
Max
Unit
10.1
1.38
1.65
1.93
2.2
1.3
°C
°C
V
A
A
A
A
V
4.3
4.6
4.0
4.9
V
V
V
V
All limits at temperature extremes are guaranteed via correlation using standard statistical quality control (SQC).
Two LEDs are used for this parameter.
RECOMMENDED SPECIFICATIONS: INPUT AND OUTPUT CAPACITANCE AND INDUCTANCE
Table 2.
Parameter
CAPACITANCE
Input
Output
MINIMUM AND MAXIMUM INDUCTANCE
Symbol
CMIN
L
Conditions
Min
TA = −40°C to +125°C
TA = −40°C to +125°C
TA = −40°C to +125°C
4.0
4.0
1.5
Rev. 0 | Page 4 of 24
Typ
Max
Unit
20
2.8
μF
μF
μH
ADP1655
I2C-COMPATIBLE INTERFACE TIMING SPECIFICATIONS
Table 3.
Parameter 1
fSCL
tHIGH
tLOW
tSU, DAT
tHD, DAT
tSU, STA
tHD, STA
tBUF
tSU, STO
tR
tF
tSP
CB
2
Max
400
0.6
1.3
100
0
0.6
0.6
1.3
0.6
20 + 0.1 CB 2
20 + 0.1 CB
0
Unit
kHz
μs
μs
ns
μs
μs
μs
μs
μs
ns
ns
ns
pF
0.9
300
300
50
400
Description
SCL clock frequency
SCL high time
SCL low time
Data setup time
Data hold time
Setup time for repeated start
Hold time for start/repeated start
Bus free time between a stop and a start condition
Setup time for stop condition
Rise time of SCL and SDA
Fall time of SCL and SDA
Pulse width of suppressed spike
Capacitive load for each bus line
Guaranteed by design.
CB is the total capacitance of one bus line in picofarads.
SDA
tLOW
tR
tF
tSU, DAT
tF
tHD, STA
tSP
tBUF
tR
SCL
S
tHD, DAT
tHIGH
tSU, STA
Sr
S = START CONDITION
Sr = REPEATED START CONDITION
P = STOP CONDITION
tSU, STO
P
S
08028-003
1
Min
Figure 3. I2C-Compatible Interface Timing Diagram
Rev. 0 | Page 5 of 24
ADP1655
ABSOLUTE MAXIMUM RATINGS
THERMAL RESISTANCE
Table 4.
Parameter
VIN, SDA/EN2, SCL/EN1, I2C/EN,
STROBE, TORCH, TX_MASK to SGND
LED_OUT, SW, VOUT to SGND
PGND to SGND
VOUT to LED_OUT
Ambient Temperature Range (TA)
Junction Temperature Range (TJ)
Storage Temperature
ESD Human Body Model
ESD Charged Device Model
ESD Machine Model
θJA of the package is based on modeling and calculation using
a 4-layer board. θJA is highly dependent on the application and
board layout. In applications where high maximum power dissipation exists, attention to thermal board design is required. The
value of θJA may vary, depending on PCB material, layout, and
environmental conditions. The specified value of θJA is based
on a 4-layer, 4 in × 3 in, 2 1/2 oz copper board, per JEDEC
standards. For more information, see the AN-617 Application
Note, MicroCSPTM Wafer Level Chip Scale Package.
Rating
−0.3 V to +6 V
−0.3 V to +12 V
−0.3 V to +0.3 V
−0.3 V to +6 V
−40°C to +85°C
−40°C to +125°C
JEDEC J-STD-020
±2000 V
±1000 V
±200 V
θJA is specified for a device mounted on a JEDEC 2S2P PCB.
Table 3. Thermal Resistance
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Package Type
12-Ball WLCSP
ESD CAUTION
THERMAL DATA
The ADP1655 may be damaged if the junction temperature
limits are exceeded. Monitoring TA does not guarantee that TJ
is within the specified temperature limits. In applications with
high power dissipation and poor thermal resistance, the maximum
TA may have to be derated. In applications with moderate power
dissipation and low PCB thermal resistance, the maximum TA
can exceed the maximum limit as long as the TJ is within specification limits. TJ of the device is dependent on the TA, the power
dissipation (PD) of the device, and the junction-to-ambient
thermal resistance (θJA) of the package. Maximum TJ is
calculated from the TA and PD using the following formula:
TJ = TA + (PD × θJA)
Rev. 0 | Page 6 of 24
θJA
75
Unit
°C/W
ADP1655
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
BALL A1
INDICATOR
1
2
3
PGND
SGND
VIN
A
SW
TORCH TX_MASK
B
VOUT
STROBE
I2C/EN
C
LED_OUT SDA/EN2 SCL/EN1
TOP VIEW
(BALL SIDE DOWN)
Not to Scale
08028-004
D
Figure 4. Pin Configuration
Table 5. Pin Function Descriptions
Pin No.
A1
A2
A3
Mnemonic
PGND
SGND
VIN
Type
Ground
Ground
Supply
B1
B2
B3
SW
TORCH
TX_MASK
Output
Digital Input
Digital Input
C1
VOUT
Output
C2
STROBE
Digital Input/
Output
C3
I2C/EN
Digital Input
D1
LED_OUT
Output
D2
SDA/EN2
Digital Input/
Output
D3
SCL/EN1
Digital Input
Description
Ground for Internal Switching FET.
Connect this pin at a single point to the power ground.
Connect the battery between VIN and PGND. Bypass VIN with a 10 μF, 6.3 V or greater X5R/X7R
capacitor.
Connect a 2.2 μH inductor between SW and the battery.
This pin enables the torch, provided that the device is not in flash or assist light mode.
Connect a digital signal to the TX_MASK pin. When the logic level is driven high during a flash
event the current is reduced to the torch level.
VOUT senses the output voltage of the boost converter and provides the input voltage to the LED
current source. The VOUT pin features a comparator to detect an overvoltage condition if the LED
string is open circuited. Connect a 10.0 μF capacitor between VOUT and PGND.
The STROBE input is used to synchronize the timing of the camera module to the LED driver in
I2C-compatible interface mode. In 2-bit logic interface mode, this acts as an output, indicating the
number of LEDs attached. STROBE = high indicates two LEDs, whereas STROBE = low indicates
one LED.
A logic low selects the 2-bit logic interface, whereas logic high selects I2C-compatible interface. If
I2C/EN is low and SDA/EN2 and SCL/EN1 are low, the driver enters shutdown mode with
consumption < 1 μA.
White LED Anode Connection. Connect LED_OUT to the anode of the white LED. LED_OUT is
internally connected to a programmable PMOS current source, which regulates the LED current.
Data Input/Output (SDA). In 2-bit logic interface mode, SDA/EN2 is the second input bit of the
digital interface.
Second Input Bit (EN2). In I2C mode, SDA is the data input/output of the I2C-compatible interface.
Clock Input (SCL). In 2-bit logic interface mode, SCL/EN1 is the first input bit of the digital interface.
First Input Bit (EN1). In I2C mode, SCL is the clock input of the I2C-compatible interface.
Rev. 0 | Page 7 of 24
ADP1655
TYPICAL PERFORMANCE CHARACTERISTICS
L = FDSE0312-2R2M
COUT = 10µF
Δ: 335µs
600
500
400
ILED (mA)
1
300
2
200
3.2
3.7
4.2
4.7
5.2
INPUT VOLTAGE (V)
50µs/DIV
CHANNEL 1 (IL) 0.5A/DIV
CHANNEL 3 (VOUT) 5V/DIV
CHANNEL 2 (I HPLED ) 0.2A/DIV
CHANNEL 4 (STROBE) 5V/DIV
Figure 5. Maximum Current vs. Input Voltage, One LED
08028-008
2.7
4
08028-005
0
3
ILIMIT – 2.00A
ILIMIT – 1.75A
ILIMIT – 1.50A
ILIMIT – 1.25A
100
Figure 8. Startup, Two LEDs Flash Mode, ILED = 400 mA, VIN = 3.6 V
L = FDSE0312-2R2M
COUT = 10µF
Δ: 180µs
450
400
350
1
ILED (mA)
300
250
2
200
150
100
3
ILIMIT – 2.00A
ILIMIT – 1.75A
ILIMIT – 1.50A
ILIMIT – 1.25A
3.2
3.7
4.2
4.7
5.2
INPUT VOLTAGE (V)
Figure 6. Maximum Current vs. Input Voltage, Two LEDs;
LED Forward Voltage (Vf) = 4.3 V for each LED
L = FDSE0312-2R2M
COUT = 10µF
50µs/DIV
CHANNEL 1 (IL) 0.5A/DIV
CHANNEL 3 (VOUT) 5V/DIV
CHANNEL 2 (I HPLED ) 0.2A/DIV
CHANNEL 4 (SCL) 5V/DIV
08028-009
0
2.7
4
08028-006
50
Figure 9. Startup, Two LEDs Assist Light Mode, ILED = 40 mA, VIN = 3.2 V
L = FDSE0312-2R2M
COUT = 10µF
Δ: 335µs
Δ: 180µs
1
1
2
3
3
4
4
50µs/DIV
CHANNEL 3 (VOUT) 5V/DIV
CHANNEL 1 (IL) 0.5A/DIV
CHANNEL 2 (I HPLED ) 0.2A/DIV
CHANNEL 4 (SCL) 5V/DIV
08028-007
50µs/DIV
CHANNEL 3 (VOUT) 5V/DIV
CHANNEL 1 (IL) 0.5A/DIV
CHANNEL 4 (STROBE) 5V/DIV
CHANNEL 2 (I HPLED ) 0.2A/DIV
08028-010
2
Figure 10. Startup, Two LEDs Torch Mode, ILED = 40 mA, VIN = 3.6 V
Figure 7. Startup, Two LEDs Flash Mode, ILED = 400 mA, VIN = 3.2 V
Rev. 0 | Page 8 of 24
ADP1655
L = FDSE0312-2R2M
COUT = 10µF
100
VIN = 3.2V
VIN = 3.6V
VIN = 4.2V
90
80
EFFICIENCY (%)
70
1
3
60
50
40
30
2
20
4
10
100
1000
08028-014
0
10
08028-011
500ns/DIV
CHANNEL 3 (LED_OUT) 5V/DIV
CHANNEL 1 (IL) 0.2A/DIV
CHANNEL 2 (I HPLED ) 0.1A/DIV
CHANNEL 4 (SW) 5V/DIV
OUTPUT CURRENT (A)
Figure 14. Efficiency PLED/PIN, Two High Power White LEDs in Series
Figure 11. Inductor Current, Two LEDs Flash Mode, ILED = 400 mA, VIN = 3.6 V
L = FDSE0312-2R2M
COUT = 10µF
100
VIN = 3.2V
VIN = 3.6V
VIN = 4.2V
90
80
EFFICIENCY (%)
70
1
2
60
50
40
30
3
20
4
0
10
08028-012
500ns/DIV
CHANNEL 3 (LED_OUT) 5V/DIV
CHANNEL 1 (IL) 0.2A/DIV
CHANNEL 2 (I HPLED ) 0.02A/DIV
CHANNEL 4 (SW) 5V/DIV
Figure 15. Efficiency PLED/PIN, One High Power White LED
L = FDSE0312-2R2M
COUT = 10µF
VIN = 3.2V
VIN = 3.6V
VIN = 4.2V
8
1k
OUTPUT CURRENT (A)
Figure 12. Inductor Current, Two LEDs Torch Mode, ILED = 40 mA, VIN = 3.6 V
10
100
08028-015
10
Δ: 4µs
1
4
2
2
0
–2
–6
3
–8
4
–10
0
100
200
300
400
OUTPUT CURRENT (mA)
500
Figure 13. LED Current Accuracy vs. Output Current
20µs/DIV
CHANNEL 3 (VOUT) 5V/DIV
CHANNEL 1 (IBAT) 1A/DIV
CHANNEL 4 (TX_MASK) 5V/DIV
CHANNEL 2 (I HPLED ) 0.2A/DIV
Figure 16. Tx Masking Response, TX_MASK = 0 V to 1.8 V,
ILED = 40 mA to 400 mA, VIN = 3.2 V
Rev. 0 | Page 9 of 24
08028-016
–4
08028-013
ILED ACCURACY (%)
6
ADP1655
L = FDSE0312-2R2M
COUT = 10µF
L = FDSE0312-2R2M
COUT = 10µF
Δ: 260µs
1
Δ: 15mA
2
3
4
1
Figure 17. Tx Masking Response, TX_MASK = 1.8 V to 0 V,
ILED = 40 mA to 400 mA, VIN = 3.2 V
08028-020
100µs/DIV
CHANNEL 1 (VIN) 0.5V/DIV
CHANNEL 2 (I HPLED ) 20mA/DIV
08028-017
100µs/DIV
CHANNEL 3 (VOUT) 5V/DIV
CHANNEL 1 (IBAT) 1A/DIV
CHANNEL 4 (TX_MASK) 5V/DIV
CHANNEL 2 (I HPLED ) 0.2A/DIV
Figure 20. Line Transient, VIN = 3.2 V to 3.6 V, ILED = 400 mA
2.4
VIN = 3.2V
VIN = 3.6V
VIN = 4.2V
PEAK CURRENT LIMIT (A)
2.2
1
2
2.0
1.8
1.6
1.4
1.2
–40
08028-018
200ms/DIV
CHANNEL 3 (SCL) 5V/DIV
CHANNEL 1 (IHPLED ) 0.1A/DIV
CHANNEL 2 (STROBE) 1V/DIV
–20
0
20
40
60
08028-021
3
80
TEMPERATURE (°C)
Figure 18. Assist Light and Flash, STROBE Edge Sensitive Mode, Two LEDs,
Timer = 850 ms, ILED = 40 mA to 400 mA, VIN = 3.6 V
Figure 21. Coil Peak Current Limit vs. Temperature, Output Mode Register =
00, 01, 10, and 11 (Binary)
1.2
VIN = 2.5V
VIN = 3.6V
VIN = 4.5V
SHUTDOWN CURRENT (µA)
1.0
1
2
0.8
0.6
0.4
0.2
0
–40
08028-019
200ms/DIV
CHANNEL 3 (SCL) 5V/DIV
CHANNEL 1 (IHPLED ) 0.1A/DIV
CHANNEL 2 (STROBE) 1V/DIV
–20
0
20
40
60
TEMPERATURE (°C)
Figure 19. Assist Light and Flash, STROBE Level Sensitive Mode, Two LEDs,
ILED = 40 mA to 400 mA, VIN = 3.6 V
Rev. 0 | Page 10 of 24
Figure 22. Shutdown Current vs. Temperature vs. VIN
80
08028-022
3
ADP1655
7.0
44
VIN = 3.2V
VIN = 3.6V
VIN = 4.2V
6.5
VIN = 3.0V
VIN = 3.6V
VIN = 5.5V
42
ILED (mA)
IVIN (mA)
6.0
5.5
40
5.0
38
0
20
40
60
80
TEMPERATURE (°C)
36
–40
ILED (mA)
405
2.0
395
1.0
390
0.5
385
20
40
60
80
100
120
TEMPERATURE (°C)
VIN = 3.2V
VIN = 3.6V
VIN = 4.2V
2.05
2.00
1.95
1.90
–20
0
20
40
60
80
100
TEMPERATURE (°C)
120
08028-025
SWITCHING FREQUENCY (MHz)
2.15
1.85
–40
100
120
VIN = 3.0V
VIN = 3.6V
VIN = 5.5V
380
–40
–20
0
20
40
60
80
100
TEMPERATURE (°C)
Figure 27. LED Regulation, Set at 400 mA,
Current Set Register = 1010 (Binary)
Figure 24. Standby Current vs. Temperature vs. VIN,
I2C/EN = SCL/EN1 = SDA/EN2 = 1.8 V
2.10
80
400
1.5
08028-024
STANDBY CURRENT (µA)
2.5
0
60
415
410
–20
40
420
3.0
0
–40
20
Figure 26. LED Regulation, Set at 40 mA,
Current Set Register = 001 (Binary)
VIN = 2.5V
VIN = 3.6V
VIN = 4.5V
3.5
0
TEMPERATURE (°C)
Figure 23. Operating Quiescent Current vs. Temperature, Torch Mode
4.0
–20
Figure 25. Switching Frequency vs. Temperature vs. VIN
Rev. 0 | Page 11 of 24
120
08028-027
–20
08028-023
4.0
–40
08028-026
4.5
ADP1655
THEORY OF OPERATION
converter is sensed at VOUT. If the output voltage exceeds
the 9.5 V (typical) limit, the white LED driver turns off and
indicates that a fault condition has occurred through the system
registers. This feature prevents damage due to an overvoltage if
the white LED string fails with an open-circuit condition.
The ADP1655 is a high power, white LED driver ideal for
driving white LEDs for use as a camera flash. The ADP1655
includes a boost converter and a current regulator suitable
for powering one or two high power, white LEDs.
The ADP1655 responds to a 2-pin control interface that can
operate in two separate pin-selectable modes: tying the I2C/
EN pin high enables the I2C interface; tying the I2C/EN pin
low enables a 2-bit logic interface.
Setting the LED regulation currents depends on the 2-pin
control interface used.
ASSIST LIGHT AND TORCH MODES
WHITE LED DRIVER
The ADP1655 features a programmable assist light mode that
provides continuous LED current. The STROBE pin or the 2-bit
logic interface can be used to transition from assist light mode
directly to flash mode. The TORCH pin provides an alternative
means of accessing a continuous LED current mode of operation. Both assist light and torch modes deliver the same current,
which is programmable via the I2C-compatible interface.
The ADP1655 drives a synchronous boost converter to power
one or two series-connected, high power LEDs. The white
LED driver regulates the high power LED current for accurate
brightness control. The ADP1655 uses an integrated PFET
current regulator.
When the white LED is turned on, the step-up converter output
voltage slew is limited to prevent excessive battery current while
charging the output capacitor. The output voltage of the boost
INPUT VOLTAGE = 2.5V TO 5.5V
COUT
CIN
L1
PGND
PGND
VIN
VOUT
SW
A3
B1
C1
HPLED
DRIVER
9.5V
2.5V
UVLO
CURRENT
SENSE
COUT
DETECTOR
OVP
CURRENT
SENSE
PWM
CONTROLLER
LED_OUT
D1
I2C/EN C3
FAULT
REGISTER
SCL/EN1 D3
SDA/EN2 D2
TORCH B2
STROBE C2
THERMAL
PROTECTION
INTERFACE
AND
CONTROL
4.35V
HPLED
SHORT
HIGH POWER LED
CURRENT CONTROL
PGND
TX_MASK B3
AGND
A1
PGND
PGND
Figure 28. Detailed Block Diagram
Rev. 0 | Page 12 of 24
08028-029
A2
SGND
ADP1655
2-BIT LOGIC INTERFACE MODE (I2C/EN = 0)
I2C INTERFACE MODE (I2C/EN = 1)
In 2-bit logic interface mode, the two control pins, EN1 and
EN2, select whether the part is disabled or operating in assist
light mode or flash mode, as outlined in Table 6. Additionally,
the TORCH pin selects torch mode.
The ADP1655 includes an I2C-compatible serial interface for
control of the LED current, as well as for a readback of system
status registers. The I2C chip address is 0x60 in write mode and
0x61 in read mode.
Figure 29 illustrates state transitions of 2-bit logic mode controlled by digital inputs EN1, EN2, TORCH, and TX_MASK.
Table 7. I2C Interface Mode Selection
Mode
Standby
Torch
Assist light
Flash
EN1 = 1
EN2 = 1
FLASH
EN1 = 1
EN1 = 0
EXTERNAL
TORCH
EN1 = 0
EN2 = 1
1
ASSIST
LIGHT
EN1 = 1 EN1 = 0
EN2 = 1 EN2 = 0
2
TIMEOUT
TORCH = 0
SHUTDOWN
TORCH = 1
Figure 29. 2-Bit Logic Mode State Transitions (I2C/EN = 0)
When the ADP1655 is in flash mode, the TX_MASK pin can
be used to reduce the battery load. The device remains in flash
mode, but the LED driver output current is reduced to the assist
light level.
Table 6. 2-Bit Logic Interface Mode Selection
Mode
Shutdown
Torch
I2C/
EN
0
0
EN1
0
0
EN2
0
0
TORCH
0
1
Assist light
0
0
1
X
Reserved
Flash
0
0
1
1
0
1
X
X
SCL
X
X
X
X
SDA
X
X
X
X
TORCH
0
1
X
X
Output Current
0 mA
20 mA to 160 mA1, 2
20 mA to 160 mA2
200 mA to 500 mA2
Torch mode has to be enabled from Register 0x04.
The output current value depends on the register settings.
Registers values are reset to the default values when VIN supply
falls below the undervoltage (UVLO) level.
EN2 = 0
08028-030
EN2 = 1
I2C/
EN
1
1
1
1
Output Current
0 mA
One LED: 80 mA
Two LEDs: 40 mA
One LED: 80 mA
Two LEDs: 40 mA
0 mA
One LED: 500 mA
Two LEDs: 320 mA
Figure 30 illustrates the I2C write sequence to a single register.
The subaddress content selects which of the five ADP1655
registers is written to first. The ADP1655 sends an acknowledgement to the master after the 8-bit data byte has been written.
The ADP1655 increments the subaddress automatically and starts
receiving a data byte to the following register until the master
sends an I2C stop as shown in Figure 31. Figure 32 shows the
I2C read sequence of a single register. ADP1655 sends the data
from the register denoted by the subaddress and increments
the subaddress automatically, sending data from the next register until the master sends an I2C stop condition as shown in
Figure 33.
State transitions between standby, assist light, flash, and
external torch modes are described in the State Transitions
section and Figure 34.
The register definitions are shown in the I2C Register Map
section. The lowest bit number (0) represents the least
significant bit, and the highest bit number (7) represents
the most significant bit.
Rev. 0 | Page 13 of 24
ADP1655
MASTER
STOP
0 = WRITE
0
0
0
0
0
0
0
CHIP ADDRESS
SUBADDRESS
S
P
0
ADP1655 RECEIVES
DATA
08028-032
1
ADP1655 ACK
1
ADP1655 ACK
0
ADP1655 ACK
S
T
Figure 30. I2C Single Register Write Sequence
MASTER
STOP
0
0
0
0
CHIP ADDRESS
0
SUBADDRESS
REGISTER N
0
ADP1655 RECEIVES
DATA TO REGISTER N
0
ADP1655 RECEIVES
DATA TO REGISTER N + 1
0
ADP1655 RECEIVES
DATA TO LAST REGISTER
S
P
ADP1655 ACK
0
ADP1655 ACK
0
ADP1655 ACK
1
ADP1655 ACK
1
ADP1655 ACK
Figure 31. I2C Multiple Register Write Sequence
CHIP ADDRESS
SUBADDRESS
1
0 1 1 0 0 0 0 1 0 0
CHIP ADDRESS
ADP1655 SENDS
DATA
S
P
08028-034
0 S
T
0 0 0
ADP1655 ACK
0 1 1 0 0 0
ADP1655 ACK
S
T
MASTER
STOP
1 = READ
MASTER ACK
0 = WRITE
ADP1655 ACK
Figure 32. I2C Single Register Read Sequence
SUBADDRESS
REGISTER N
CHIP ADDRESS
ADP1655 SENDS
DATA OF REGISTER N
0
Figure 33. I2C Multiple Register Read Sequence
Rev. 0 | Page 14 of 24
1 S
P
0
ADP1655 SENDS
DATA OF
REGISTER N + 1
ADP1655 SENDS
DATA OF LAST
REGISTER
08028-035
CHIP ADDRESS
0 1 1 0 0 0 0 1 0 0
MASTER ACK
0 S
T
0 0 0
MASTER ACK
0 1 1 0 0 0
MASTER ACK
S
T
MASTER
STOP
1 = READ
ADP1655 ACK
0 = WRITE
ADP1655 ACK
0
ADP1655 ACK
S
T
08028-033
0 = WRITE
ADP1655
STATE TRANSITIONS
When the ADP1655 is in flash mode, the TX_MASK pin can
be used to reduce the battery load. The device remains in flash
mode, but the LED driver output current is reduced to the assist
light level. In Figure 34, if the flash was triggered by the strobe
pin in level-sensitive mode, a timeout triggers a timeout fault,
as defined in the Safety Features section.
TX_MASK ENABLED
TX_MASK = 1
MODE = ASSIST LIGHT
STROBE = 1
TX_MASK = 0
OUTPUT ON
STROBE DISABLED
MODE = FLASH
FLASH
OUTPUT ON
STROBE = 1
OUTPUT ON
STROBE = 1
STROBE DISABLED
MODE = FLASH
TX_MASK = 0
EN1 = 0
EN2 = 1
ASSIST
LIGHT
OUTPUT ON
STROBE DISABLED
MODE = FLASH
TIMEOUT
OUTPUT OFF
OUTPUT ON
MODE = ASSIST LIGHT
OUTPUT OFF
STANDBY
I2C/EN = 1
TORCH NOT
ALLOWED
TORCH = 0
TORCH ALLOWED
MODE = TORCH
Figure 34. I2C Interface Mode: State Transitions
Rev. 0 | Page 15 of 24
08028-036
EXTERNAL
TORCH
ADP1655
I2C REGISTER MAP
The lowest bit number (0) represents the least significant bit, and the highest bit number (7) represents the most significant bit.
Table 8. Design Information Register (Register 0x00)
Bit
7:0
R/W
R
Reset State
00100001
Table 9. Version Register (Register 0x01)
Bit
7:0
R/W
R
Reset State
00000001
Table 10. VREF and Timer Register (Register 0x02)
Bit
7:6
5:4
R/W
R/W
R/W
3:0
R/W
Description
Reserved
Number of LEDs detection comparator reference level
00 = 4.3 V (default)
01 = 4.6 V
10 = 4.0 V
11 = 4.9 V
Flash timer value setting
0000 = 100 ms
0001 = 150 ms
0010 = 200 ms
0011 = 250 ms
0100 = 300 ms
0101 = 350 ms
0110 = 400 ms
0111 = 450 ms
1000 = 500 ms
1001 = 550 ms
1010 = 600 ms
1011 = 650 ms
1100 = 700 ms
1101 = 750 ms
1110 = 800 ms
1111 = 850 ms (default)
Rev. 0 | Page 16 of 24
ADP1655
Table 11. Current Set Register (Register 0x03)
Bit
7:4
R/W
R/W
3
2:0
R/W
Description
Flash current value setting
0000 = 200 mA
0001 = 220 mA
0010 = 240 mA
0011 = 260 mA
0100 = 280 mA
0101 = 300 mA
0110 = 320 mA (default for two LEDs)
0111 = 340 mA
1000 = 360 mA
1001 = 380 mA
1010 = 400 mA
1011 = 420 mA
1100 = 440 mA
1101 = 460 mA
1110 = 480 mA
1111 = 500 mA (default for one LED)
N/A
Torch and assist light current value setting
000 = 20 mA
001 = 40 mA (default)
010 = 60 mA
011 = 80 mA
100 = 100 mA
101 = 120 mA
110 = 140 mA
111 = 160 mA
Table 12. Output Mode Register (Register 0x04)
Bit
7:6
R/W
R/W
5
R/W
4
R/W
3
R/W
2
R/W
1:0
R/W
Description
Inductor peak current limit setting
00 = 1.25 A
01 = 1.5 A
10 = 1.75 A (default)
11 = 2.0 A
0 = edge sensitive
1 = level sensitive (default)
0 = TORCH not allowed
1 = TORCH allowed (default)
0 = LED_OUT off (default)
1 = LED_OUT on
0 = STROBE disabled
1 = STROBE enabled (default)
Configures LED output mode
00 = standby mode (default)
01 = reserved
10 = assist light mode
11 = flash mode
Rev. 0 | Page 17 of 24
ADP1655
Table 13. Fault Information Register (Register 0x05)
Bit
7
R/W
R
6
R
5
R
4
R
3
R/W
2
1
R
R
0
R
Description
0 = no fault (default)
1 = overvoltage or COUT fault
0 = no fault (default)
1 = short-circuit fault
0 = no fault (default)
1 = overtemperature fault
0 = no fault (default)
1 = timeout 850 ms fault
0 = one LED
1 = two LEDs (default)
Reserved
0 = no fault (default)
1 = current limit fault
Reserved
Table 14. Input Control Register (Register 0x06)
Bit
7:3
2
R/W
1
R/W
0
R
R/W
Description
Reserved
0 = Strobe 0 triggers flash in level sensitive mode, Strobe 1 > 0 triggers flash in edge sensitive mode
1 = Strobe 1 triggers flash in level sensitive mode, Strobe 0 > 1 triggers flash in edge sensitive mode (default)
0 = TX_MASK function disabled
1 = TX_MASK function allowed (default)
Reserved
Rev. 0 | Page 18 of 24
ADP1655
SAFETY FEATURES
For critical system conditions, such as output overvoltage,
flash timeout, LED output short circuit, and overtemperature
conditions, the ADP1655 has built-in safety mechanisms. If
one of the fault conditions occurs, the device shuts down and
a corresponding flag is set in the fault information register
(Register 0x05). In I2C interface mode, the system baseband
processor can read the fault information register through the
I2C interface to determine the nature of the fault condition
and, consequently, the fault flag is cleared. The device is
disabled until the fault information register is cleared.
In 2-bit logic interface mode, the I2C register readback is not
available. To clear a fault, set EN1, EN2, and TORCH low.
OVERVOLTAGE FAULT
The ADP1655 contains a comparator at the VOUT pin that
monitors the voltage between VOUT and SGND. If the voltage
exceeds 9.5 V (typical), the ADP1655 shuts down. In I2C mode,
Bit 7 in the fault information register is read back as high. The
ADP1655 is disabled until the fault is cleared, ensuring protection against an open circuit.
OUTPUT CAPACITOR FAULT
If no output capacitor is present at the VOUT pin when the
ADP1655 is enabled for a flash, torch, or assist light event,
the part shuts down and Bit 7 in the fault information register
is read back as high. The ADP1655 is disabled until the fault is
cleared. The output capacitor detection scheme does not cause
the VOUT pin to rise above the overvoltage threshold even though
the overvoltage flag (Bit 7) in the fault information register
(Register 5) is set. The overvoltage and output capacitor fault
flags share a single register bit to reduce the required number
of registers.
TIMEOUT FAULT
If the 2-bit logic interface is used, the maximum duration for
flash being enabled (EN1/EN2 = 1) is preset to 850 ms. If EN1
and EN2 remain high for longer than 850 ms, ADP1655 is
disabled until the fault is cleared (EN1, EN2, and TORCH low).
In I2C mode, if strobe mode is enabled (Register 0x04, Bit 2),
strobe is set to level sensitive mode (Register 0x04, Bit 5), and
if strobe remains high for longer than 850 ms, the timeout fault
bit, Register 0x05, Bit 4), is read back as high. The ADP1655 is
disabled until the fault is cleared.
OVERTEMPERATURE FAULT
If the junction temperature of the ADP1655 rises above 150°C,
a thermal protection circuit shuts down the device. In I2C mode,
Bit 5 of the fault information register is read back as high. The
ADP1655 is disabled until the fault is cleared.
SHORT-CIRCUIT FAULT
The LED_OUT pin features short-circuit protection that
disables the ADP1655 if it detects a short circuit to ground at
the LED_OUT pin. The ADP1655 monitors the LED voltage
when the LED driver is enabled. If the LED_OUT pin remains
below the short-circuit detection threshold during startup, a
short circuit is detected. Bit 6 of the fault information register
is read back as high. The ADP1655 is disabled until the fault is
cleared.
CURRENT LIMIT
The internal switch limits battery current by ensuring that the
peak inductor current does not exceed the programmed limit
(current limit is set by Bit 6 and Bit 7 in the output mode register,
Register 0x04). If the peak inductor current exceeds the limit,
the part shuts down and Bit 1 of the fault information register
is read back as high. The ADP1655 is disabled until the fault is
cleared.
AMOUNT OF LED DETECTION
The ADP1655 is able to detect the amount of LED connected in
series between the LED_OUT pin and the PGND potential. In
I2C mode, the detection is enabled with Bit 3 in the output mode
register. The part uses an 80 mA LED driver current setting to
detect the LED forward voltage (Vf) with a voltage comparator
at the start of a flash, torch, or assist light event. If the detected
forward voltage is higher than 4.3 V (typical), Bit 3 of the fault
information register is read back as high.
INPUT UNDERVOLTAGE
The ADP1655 includes an input undervoltage lockout circuit. If
the battery voltage drops below the 2.4 V (typical) input UVLO
threshold, the ADP1655 shuts down. In this case, information
in all registers is lost, and when power is reapplied, a power-on
reset circuit resets the registers to their default conditions.
Rev. 0 | Page 19 of 24
ADP1655
APPLICATIONS INFORMATION
EXTERNAL COMPONENT SELECTION
Selecting the Inductor
The ADP1655 boost converter increases the battery voltage
to allow driving of one or two LEDs, whose combined voltage
drop is higher than the battery voltage plus the current source
headroom voltage. This allows the converter to regulate the
LED current over the entire battery voltage range and with a
wide variation of LED forward voltage.
The inductor saturation current should be greater than the sum
of the dc input current and half the inductor ripple current. A
reduction in the effective inductance due to saturation increases
the inductor current ripple. Suggested inductors are shown in
Table 15.
Table 15. Suggested Inductors
Vendor
Toko
Toko
Coilcraft
Coilcraft
Value
(μH)
2.2
2.0
2.2
2.2
Part No.
FDSE0312
DE2812C
LPS3010
LPS3314
DCR
(mΩ)
160
67
220
100
ISAT
(A)
3.1
1.8
1.4
1.5
Dimensions
L × W × H (mm)
3 × 3 × 1.2
3.0 × 3.2 × 1.22
3 × 3 × 1.0
3 × 3 × 1.4
Selecting the Input Capacitor
The ADP1655 requires an input bypass capacitor to supply
transient currents while maintaining constant input and output
voltages. The input capacitor carries the input ripple current,
allowing the input power source to supply only the dc current.
Use an input capacitor with a sufficient ripple current rating to
handle the inductor ripple. Increased input capacitance reduces
the amplitude of the switching frequency ripple on the battery.
Because of the dc bias characteristics of ceramic capacitors, a
0603, 6.3 V X5R/X7R, 10 μF ceramic capacitor is preferable.
Higher value input capacitors help to reduce the input voltage
ripple and improve transient response. Maximum input
capacitor current is calculated using the following equation:
I CIN ≥ I LOAD( MAX )
VOUT (VIN − VOUT )
VIN
To minimize supply noise, place the input capacitor as close to
the VIN pin of the ADP1655 as possible. As with the output
capacitor, a low ESR capacitor is suggested. A list of suggested
input capacitors is shown in Table 16.
Table 16. Suggested Input Capacitors
Vendor
Murata
TDK
Tayio
Yuden
Value
10 μF, 6.3 V
10 μF, 6.3 V
10 μF, 6.3 V
Part No.
GRM188R60J106ME47
C1608JB0J106K
JMK107BJ106MA
Dimensions
L × W × H (mm)
1.6 × 0.8 × 0.8
1.6 × 0.8 × 0.8
1.6 × 0.8 × 0.8
Selecting the Output Capacitor
The output capacitor maintains the output voltage and supplies
the LED current during NFET power switch on period. It also
stabilizes the loop. A 10.0 μF, 16 V X5R/X7R ceramic capacitor
is suggested.
Note that dc bias characterization data is available from capacitor manufacturers and should be taken into account when
selecting input and output capacitors. 16 V capacitors are
recommended for most two-LED designs. Designs with 1 mm
height restrictions can also use 0603 case size, 16 V capacitors
in parallel. A list of suggested output capacitors is shown in
Table 17.
Table 17. Suggested Output Capacitors
Vendor
Murata
Murata
Tayio
Yuden
Value
10.0 μF, 10 V
10.0 μF, 16 V
10.0 μF, 16 V
Part No.
GRM21BR71A106KE51
GRM31CR61C106KA88
EMK212BJ106KG
Dimensions
L × W × H (mm)
2 × 1.25 × 1.25
3.2 × 1.6 × 1.6
2 × 1.25 × 1.25
Higher output capacitor values reduce the output voltage ripple
and improve load transient response. When choosing this value,
it is also important to account for the loss of capacitance due to
output voltage dc bias.
Ceramic capacitors are manufactured with a variety of dielectrics, each with different behavior over temperature and applied
voltage. Capacitors must have a dielectric that ensures the
minimum capacitance over the necessary temperature range
and dc bias conditions. X5R or X7R dielectrics with a voltage
rating of 10.0 V or 16 V are suggested for best performance.
Y5V and Z5U dielectrics are not suggested for use with any
dc-to-dc converter because of their poor temperature and dc
bias characteristics.
Rev. 0 | Page 20 of 24
ADP1655
The worst-case capacitance accounting for capacitor variation
over temperature, component tolerance, and voltage is calculated using the following equation:
CEFF = COUT × (1 − TEMPCO) × (1 − TOL)
where:
CEFF is the effective capacitance at the operating voltage.
TEMPCO is the worst-case capacitor temperature coefficient.
TOL is the worst-case component tolerance.
In this example, TEMPCO over −40°C to +85°C is assumed to
be 15% for an X5R dielectric, TOL is assumed to be 10%, and
COUT is 9.528 μF at 1.8 V, as shown in Figure 35.
To guarantee the performance of the ADP1655, it is imperative
that the effects of dc bias, temperature, and tolerances on the
behavior of the capacitors be evaluated for each application.
The peak-to-peak output voltage ripple for the selected output
capacitor and inductor values is calculated using the following
equation:
VRIPPLE =
ESRCOUT ≤
CEFF = 9.528 μF × (1 − 0.15) × (1 − 0.1) = 7.288 μF
I RIPPLE
8 × f SW × C OUT
VRIPPLE
I RIPPLE
The effective capacitance needed for stability, which includes
temperature and dc bias effects, is 4 μF.
12
10
CAPACITANCE (µF)
=
Capacitors with lower equivalent series resistance (ESR) are
preferred to guarantee low output voltage ripple, as shown in
the following equation:
Substituting these values in the equation yields
8
6
4
0
2
4
6
8
10
DC BIAS VOLTAGE (V)
12
14
16
08028-037
2
0
V IN
(2π × f SW ) × 2 × L × C OUT
Figure 35. DC Bias Characteristic of a 16 V, 10 μF Ceramic Capacitor
Rev. 0 | Page 21 of 24
ADP1655
PCB LAYOUT
•
Poor layout can affect performance, causing electromagnetic
interference (EMI) and electromagnetic compatibility (EMC)
problems, ground bounce, and voltage losses. Poor layout can
also affect regulation and stability. A good layout is implemented
using the following rules and shown in Figure 36:
•
Place the inductor, input capacitor, and output capacitor
close to the IC using short tracks. These components carry
high switching frequencies and large tracks act as antennas.
VIN
PGND
INPUT
CAPACITOR
PGND
HIGH
POWER
LED
ADP1655
INDUCTOR
OUTPUT
CAPACITOR
HIGH
POWER
LED
08028-028
•
•
Route the output voltage path away from the inductor and
SW node to minimize noise and magnetic interference.
Maximize the size of ground metal on the component side
to help with thermal dissipation.
Use a ground plane with several vias connecting to the
component side ground to further reduce noise interference on sensitive circuit nodes.
Figure 36. Example Layout of the ADP1655 Driving Two White LEDs
Rev. 0 | Page 22 of 24
ADP1655
OUTLINE DIMENSIONS
0.660
0.602
0.544
1.54
1.50
1.46
0.022
REF
SEATING
PLANE
3
2
1
A
BALL A1
IDENTIFIER
2.04
2.00
1.96
0.330
0.310
0.290
B
1.50
REF
C
D
0.380
0.352
0.324
0.04 MAX
COPLANARITY
0.280
0.250
0.220
BOTTOM VIEW
(BALL SIDE UP)
1.00
REF
020409-B
TOP VIEW
(BALL SIDE DOWN)
0.50
REF
Figure 37. 12-Ball Wafer Level Chip Scale Package [WLCSP]
(CB-12-4)
Dimensions shown in millimeters
ORDERING GUIDE
Model
ADP1655ACBZ-R7 1
ADP1655-EVALZ1
1
Temperature Range
–40°C to +125°C
Package Description
12-Ball Wafer Level Chip Scale Package [WLCSP]
Evaluation Board
Z = RoHS Compliant Part.
Rev. 0 | Page 23 of 24
Package Option
CB-12-4
Branding
LAM
ADP1655
NOTES
©2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08028-0-5/09(0)
Rev. 0 | Page 24 of 24
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