ADP5520 datasheet(9/40 Pages) AD

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ADP5520

Rev. 0 | Page 9 of 40

THEORY OF OPERATION

PGND

VBAT

VDDIO

SCL

SDA

nINT

nRST

ADP5520

4.7µH

1µF

VBAT

BST

BL_SNK

CAP_OUT

100nF

GND GND GND

CMP_IN

ILED

STATE MACHINE

INTERRUPT/RESET

CONTROL

INTERFACE

BIAS/CLOCK

LIGHT

SENSOR

LED

CURRENT

CONTROL

POR

LDO

I/O CONFIG

GPIO/KEYPAD

OUT

2.7V

THERMAL S/D

BACKLIGHT

CURRENT

CONTROL

27V

BOOST

CONTROL

0.65V

OVP

AUTO

LOAD

I-LIMIT

VBAT

Figure 13. Internal Block Diagram

The ADP5520 is a backlight white LED driver with an I/O port

expander. It is ideal for cell phone designs and other portable

devices, where keypad and/or extended I/O functionality is

needed. Programmable fade-in, fade-out, dim, and off timers

provide the backlight with flexible control features. Using an

external photodiode, the ADP5520 can perform ambient light

sensing, and adjust the backlight brightness according to

varying lighting conditions.

The I/O port expander has eight configurable GPIO pins. The

I/Os can be configured as a keypad matrix, digital inputs, or

digital outputs. Additionally, two of the I/Os (R3 and C3) can be

configured as current sink lines and, paired with a dedicated

sink line (ILED), can be used to drive up to three auxiliary LEDs.

Programmable fading is also available for auxiliary LEDs.

Once programmed through its I2C-compatible interface, the

ADP5520 can run autonomously. An interrupt line (nINT) is

available to alert an external microprocessor of the status of its

I/Os, keypad presses and releases, ambient light sensor comparator

states, and overvoltage conditions.

BACKLIGHT DRIVE AND CONTROL

White LEDs are common in backlighting the displays of modern

portable devices such as cell phones. White LEDs require a high

forward voltage, VF, before they conduct current and emit light.

Display panels, depending on their size, can be backlit with

single or multiple white LEDs. In panels that require multiple

LEDs, the LEDs are commonly connected in a series string to

achieve uniform brightness in each LED by passing a common

current through all of them. The LED string needs to be biased

with a voltage greater than the sum of the VF of each LED

before it conducts.

The ADP5520 is an asynchronous boost converter capable of

driving an LED string with 24.5 V (minimum). For detailed

information about the boost device, see the Applications

Information section. With sufficient forward voltage created,

the ADP5520 controls the current (and thus the brightness)

of the LED string via an adjustable internal current sink. An

internal state machine, in conjunction with programmable

timers, dynamically adjusts the current sink between 0 mA

and 30 mA to achieve impressive backlight control features.

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