Camera Phone LED Flash
The LM3642 is a 4-MHz fixed-frequency synchronous boost converter plus 1.5-A constant current driver for a high-current white LED. The high-side current source allows for grounded cathode LED operation providing Flash current up to 1.5 A. An adaptive regulation method ensures the current source remains in regulation and maximizes efficiency.
The LM3642 is controlled via an I2C-compatible interface. Features include a hardware flash enable (STROBE) allowing a logic input to trigger the flash pulse as well as a TX input which forces the flash pulse into a low-current Torch Mode, allowing for synchronization to RF power amplifier events or other high-current conditions.
The 4-MHz switching frequency, overvoltage protection and adjustable current limit settings allow the use of tiny, low-profile inductors and (10-µF) ceramic capacitors. The device is available in a small 9-bump DSBGA package and operates over the −40°C to 85°C temperature range.
PART NUMBER | PACKAGE | BODY SIZE (MAX) |
---|---|---|
LM3642 | DSBGA (9) | 1.69 mm × 1.64 mm |
Changes from G Revision (December 2014) to H Revision
Changes from F Revision (December 2013) to G Revision
Changes from E Revision (May 2013) to F Revision
PIN | I/O | DESCRIPTION | |
---|---|---|---|
NO. | NAME | ||
A1 | OUT | Power | Step-up DC-DC converter output. Connect a 10-µF ceramic capacitor between this pin and GND. |
A2 | SW | Power | Drain connection for internal NMOS and synchronous PMOS switches. |
A3 | GND | Ground | Ground |
B1 | LED | Output | High-side current source output for Flash LED. |
B2 | STROBE | Input | Active high hardware Flash enable. Drive STROBE high to turn on Flash pulse. Has an internal pulldown resistor of 300 kΩ between STROBE and GND. |
B3 | IN | Power | Input voltage connection. Connect IN to the input supply, and bypass to GND with a 10-µF or larger ceramic capacitor. |
C1 | TX/TORCH | Input | Configurable power amplifier synchronization input or configurable active high Torch enable. Has an internal pulldown resistor of 300 kΩ between TX and GND. |
C2 | SDA | Input/Output | Serial data input/output. |
C3 | SCL | Input | Serial clock input. |
MIN | MAX | UNIT | |
---|---|---|---|
VIN, VSW,VOUT | –0.3 | 6 | V |
VSCL, VSDA, VSTROBE, VTX, VLED | –0.3 | the lesser of (VIN+0.3) w/ Vmax | V |
Continuous power dissipation(4) | Internally limited | ||
Junction temperature (TJ-MAX) | 150 | °C | |
Maximum lead temperature (soldering) | See(5) | ||
Storage temperature, Tstg | −65 | 150 | °C |
VALUE | UNIT | |||
---|---|---|---|---|
V(ESD) | Electrostatic discharge | Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) | ±2000 | V |
MIN | MAX | UNIT | |
---|---|---|---|
VIN | 2.5 | 5.5 | V |
Junction temperature (TJ) | –40 | 125 | °C |
Ambient temperature (TA)(2) | –40 | 85 | °C |
THERMAL METRIC(1) | LM3642 | UNIT | |
---|---|---|---|
YZR (DSBGA) | |||
9 PINS | |||
RθJA | Junction-to-ambient thermal resistance | 100.0 | °C/W |
RθJC(top) | Junction-to-case (top) thermal resistance | 0.7 | °C/W |
RθJB | Junction-to-board thermal resistance | 16.4 | °C/W |
ψJT | Junction-to-top characterization parameter | 3.2 | °C/W |
ψJB | Junction-to-board characterization parameter | 16.4 | °C/W |
RθJC(bot) | Junction-to-case (bottom) thermal resistance | n/a | °C/W |
PARAMETER | TEST CONDITIONS | MIN | TYP | MAX | UNIT | ||
---|---|---|---|---|---|---|---|
CURRENT SOURCE SPECIFICATIONS | |||||||
ILED | Current source accuracy | 1-A flash, VOUT = 4 V | –6% | 1.04 | 6% | A | |
1.5-A flash, VOUT = 4 V | –8% | 1.5 | 8% | A | |||
24-mA torch, VOUT = 4 V (LM3642-LT) |
–10% | 24 | 10% | mA | |||
48.4 mA Torch, VOUT = 4 V | –10% | 48.4 | 10% | mA | |||
VHR | Current source regulation voltage | ILED = 1.5 A | Flash | 275 | 12% | mV | |
ILED = 24 mA/48.4 mA | Torch | 150 | 15% | ||||
VOVP | Output overvoltage protection trip point | ON threshold | –2.8% | 5 | 2.2% | V | |
OFF threshold | –2.7% | 4.88 | 2.3% | ||||
STEP-UP DC-DC CONVERTER SPECIFICATIONS | |||||||
RPMOS | PMOS switch on-resistance | IPMOS = 1 A | 120 | mΩ | |||
RNMOS | NMOS switch on-resistance | INMOS = 1 A | 90 | ||||
ICL | Input current limit | –17% | 1.6 | 15% | A | ||
–17% | 1.88 | 15% | |||||
VIVFM | Input voltage flash monitor trip threshold | –3.2% | 2.9 | 3.2% | V | ||
UVLO | Undervoltage threhold | Falling VIN | –4% | 2.8 | 4% | V | |
ƒSW | Switching frequency | –9% | 4 | 9% | MHz | ||
IQ | Quiescent supply current | Device not switching pass mode | 0.75 | mA | |||
ISB | Standby supply current | Device disabled 2.5 V ≤ VIN ≤ 5.5 V | 1.6 | 4 | µA | ||
tTX | Flash-to-torch LED current settling time | TX low to high ILED = 1.5 A to 24 mA/48.4 mA |
4 | µs | |||
STROBE, TX VOLTAGE SPECIFICATIONS | |||||||
VIL | Input logic low | 2.5 V ≤ VIN ≤ 5.5 V | 0 | 0.4 | V | ||
VIH | Input logic high | 2.5 V ≤ VIN ≤ 5.5 V | 1.2 | VIN | |||
I2C-COMPATIBLE INTERFACE SPECIFICATIONS (SCL, SDA) | |||||||
VIL | Input logic low | 2.5 V ≤ VIN ≤ 5.5 V | 0 | 0.4 | V | ||
VIH | Input logic high | 2.5 V ≤ VIN ≤ 4.2 V | 1.2 | VIN | |||
VOL | Output logic low | ILOAD = 3 mA | 400 | mV |
MIN | NOM | MAX | UNIT | ||
---|---|---|---|---|---|
t1 | SCL clock frequency | 2.4 | ns | ||
t2 | Data In setup time to SCL High | 100 | ns | ||
t3 | Data out stable after SCL Low | 0 | ns | ||
t4 | SDA low setup time to SCL low (start) | 100 | ns | ||
t5 | SDA high hold time after SCL high (stop) | 100 | ns |