8

FN9263.1

December 14, 2007

Typical Application Diagram

Applications Information

The ISL97645 provides a complete power solution for TFT

LCD applications. The system consists of one boost

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 ISL97645 is shut down

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

enable pin reaches 2.2V, the ISL97645 is on.

Boost Converter

Frequency Selection

The ISL97645 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 ISL97645

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.

Operation

The boost converter is a current mode PWM converter

operating at either a 650kHz or 1.2MHz. It can operate in

both discontinuous conduction mode (DCM) at light load and

FIGURE 12. TYPICAL APPLICATION DIAGRAM

BOOST

GPM

CIRCUIT

VON

ENABLE

VGH

VDD_1

VGH_M

LX

FB

VFLK

COMP

SS

POS

TO ROW DRIVER

NC

NC

VIN

GND

VDPM

FREQ-

CE

RE

PGND

VDD2

AGND

C1

22µF

C3

2.2nF

C4

10nF

S1

S2

S3

C5

470P

R3

2K

C6

0.1µF

0.47µF

R2

1.3K

R1

10K

C2

47µF

L1

10µH

D1

NEG-

OUT

+4.0V

R7

80k

C11

1µF

R6

130k

ISL97645