9

FN9228.0

April 11, 2006

Typical Application Diagram

Applications Information

The ISL97644 provides a complete power solution for TFT

LCD applications. The system consists of one boost

logic LDO regulator to provide voltage to logic circuit in the

up to 400mA peak current. This part also integrates Gate

Pulse Modulator circuit that can help to optimize the picture

quality.

Enable Control

When enable pin is pulling down, the ISL97644 is shut down

reducing the supply current to <10µA. When the voltage at

enable pin reaches 2.2V, the ISL97644 is on.

Boost Converter

Frequency Selection

The ISL97644 switching frequency can be user selected to

operate at either constant 650kHz or 1.2MHz. Lower

switching frequency can save power dissipation, while

higher switching frequency can allow smaller external

components like inductor and output capacitors, etc.

Connecting FREQ pin to ground sets the PWM switching

1.2MHz.

Soft-Start

The soft-start is provided by an internal 2.5µA current source

to charge the external soft start capacitor. The ISL97644

ramps up current limit from 0A up to full value, as the voltage

at SS pin ramps from 0 to 1.2V. Hence the soft-start time is

4.8ms when the soft-start capacitor is 10nF, 22.6ms for 47nF

and 48ms for 100nF.

BOOST

GPM

CIRCUIT

VIN2

ENABLE

VGH

VDD_1

VGH_M

LX

FB

VFLK

COMP

SS

POS

NEG-

LDO

CONTROLLER

LDO_OUT

ADJ

VIN1

GND

VDPM

FREQ-

CE

RE

OUT

PGND

VDD2

AGND

C1

22µF

C3

2.2nF

C4

10nF

C5

470P

R3

2k

C6

0.1µF

C7

4.7µF

2.2µF

R2

1.3k

R1

10k

C2

47µF

L1

10µH

D1

R5

10k

C10

FIGURE 14. TYPICAL APPLICATION DIAGRAM

C9 (OPTIONAL)

TO ROW DRIVER

+4.0V

R6

130k

R7

80k

C11

1µF

ISL97644