ADP1655ACBZ-R7 datasheet(12/24 Pages) AD

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ADP1655

Rev. 0 | Page 12 of 24

THEORY OF OPERATION

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.

WHITE LED DRIVER

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

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.

Setting the LED regulation currents depends on the 2-pin

control interface used.

ASSIST LIGHT AND TORCH MODES

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 opera-

tion. Both assist light and torch modes deliver the same current,

which is programmable via the I2C-compatible interface.

PWM

CONTROLLER

PGND

VOUT

PGND

SGND

VIN

UVLO

2.5V

OVP

FAULT

HPLED

SHORT

THERMAL

PROTECTION

HPLED

DRIVER

CURRENT

SENSE

CURRENT

SENSE

SCL/EN1

SDA/EN2

TORCH

STROBE

TX_MASK

PGND

AGND

COUT

INPUT VOLTAGE = 2.5V TO 5.5V

CIN

I2C/EN

INTERFACE

AND

CONTROL

9.5V

4.35V

COUT

DETECTOR

HIGH POWER LED

CURRENT CONTROL

LED_OUT

Figure 28. Detailed Block Diagram

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