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