ADP1653ACPZ-R21 datasheet(13/24 Pages) AD

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ADP1653

Rev. A | Page 13 of 24

THEORY OF OPERATION

The ADP1653 is a high power, white LED driver ideal for

driving white LEDs for use as a camera flash. The ADP1653

includes a step-up converter and a current regulator suitable for

powering one, or up to three, high power, white LEDs. A second

lower current sink allows an indicator LED to be driven with

2.5 mA to 17.5 mA current.

The ADP1653 responds to a 2-pin control interface that can

operate in two separate pin-selectable modes. Tying the INTF

pin high enables a 2-bit logic hardwire interface. Tying the

INTF pin low enables the I2C interface.

WHITE LED DRIVER

The ADP1653 drives a step-up converter to power typically one

or two series-connected, high power LEDs. The white LED driver

regulates the high power LED current for accurate brightness

control. The ADP1653 uses an integrated NFET current regulator

that drops the voltage when the power LED forward voltage is

less than the battery voltage.

When the required LED voltage is greater than the battery voltage,

the NFET current regulator voltage at the HPLED pin is approxi-

mately 320 mV, and the step-up converter applies the appropriate

voltage to OUT, allowing the LED to conduct the regulated current.

When the white LED is turned on, the step-up converter output

voltage slew is limited to 18 V/ms to prevent excessive battery

current while charging the output capacitor. The output voltage

of the step-up converter is sensed at OUT. If the output voltage

exceeds the 10.15 V (typical) limit, the white LED converter

turns off to indicate that a fault condition has occurred through

the INT output and system registers. This feature prevents damage

due to an overvoltage if the white LED string fails with an open-

circuit condition.

Setting the LED regulation currents depends on the 2-pin

control interface used, as described in the following sections.

ILED

CONTROL

INTERFACE/

CONTROL

PWM

CONTROLLER

OSCILLATOR

FAULT

THERMAL

PROTECTION

× 5200

= TORCH

× 20800

= FLASH

× 400

= ILED

Tx MASK (OPTIONAL)

WATCHDOG

TIMER

PGND

HPLED

GND

1.22V/RF

1.22V/RT

1.22V/RI

SETF

1.22V

IREF

(FLASH)

IREF

(TORCH)

IREF

(ILED)

1.22V

SETT

SETI

INTF

INT

VDD/2

I/O VDD

STR

CTRL0/SDA

CTRL1/SCL

10.15V

2.7V

OVP

UVLO

ILED

OUT

VDD

–

0.32V

OUT

COUT

PGND

CIN

PGND

HIGH POWER

LED CONTROL

VDD = 2.75V TO 5.5V

BIAS

Figure 25. Detailed Block Diagram

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