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ADM8840

Charge Pump Regulator & COM Driver for Color TFT Panel

Analog Devices 

PRELIMINARY TECHNICAL DATA

a

Charge Pump Regulator & COM Driver

for Color TFT Panel

Preliminary Technical Data

ADM8840

FEATURES

Programmable COM Driver to prevent Screen-Burn

3 Voltages (5.0V,15.0V,-15.0V) from one 3V Supply

Power Efficiency optimised for use with TFT in mobile

phones

Low Quiescent Current

Low Shutdown Current (<5uA)

Shutdown Function

APPLICATIONS

Handheld Instruments

TFT LCD Panels

Cellular Phones

SHDN

C6

4.7␮ F

VCC

DAC1_IN

D AC 1 _S D

FUNCTIONAL BLOCK DIAGRAM

ADM8840

OS CI L L AT O R

TIMING

G E N E R A T OR

S H UT D OW N

C ON T RO L

DI S C HARG E

CONTROL

LOGIC

VOLTAGE

IN VE RT ER

TRIP LE

VOLTAGE

TRIPLER

DOUBLE

LDO

VOLTAGE

RE G UL ATO R

V OL T AG E

DOUBLER

V O LT AGE

ADDER

C4+

C4

0.22␮F

C4-

C2+

C2

0.22␮F

C2-

C3+

C3

0. 2 2␮ F

C3-

-15V

C9 0.22␮F

+15V

C8 0.22␮F

5VIN

5V O UT

+5V

C7 2.2␮F

C1+

C1

3.3␮F

C 1-

VOUT

C10

3.3␮F

C5+

C5

3.3␮F

C5-

GENERAL DESCRIPTION

The ADM8840 combines a charge pump regulator and a

Common Line (COM) driver in a single chip solution for use

in TFT LCD’s. The device provides an LCD controller and

grayscale DAC supply voltage of 5.0V (±2%), 2 gate drive

voltages of +15V and -15V and a COM driver voltage. This

COM Driver voltage alternates the polarity of the Common

line voltage every line (or every frame) on the display in order

to prevent screen-burn occuring over time. The ADM8840

is powered by a single 3.0V supply.

The ADM8840 has an internal 100KHz oscillator for driving

the charge pumps.

The COM Driver section of the ADM8840 can be used to

generate the alternate frame or line inversion of the COM

line of the LCD panel. The ADM8840 receives the COM

clock from the controller with a frequency up to 10kHz and

allows programmable conditioning of its amplitude and

centre voltage through the use of on-board DAC’s. This

allows programmable elimination of display flicker caused

by the COM inversion.

The COM_OUT amplitude can be programmed from 4.0V

to 7.0V in steps of 28mV. The COM_OUT centre voltage

can be programmed to 0.9V to 2.8V in steps of 14mV.

VREF

CLK

D ATA

CS / LDAC

8

SERIAL

INTERFACE

8

DAC 1

DAC 2

CO M _I N

DAC2_SD

D AC 2_I N

IN T /E XT

DAC 1

INT/EXT

DAC 2

ADD _ OUT

C11

+

4.7␮F

-

LEVEL

TRANSLATOR

POWER

BUFFER

T R AN S_ O UT

C12

4.7␮F

C OM _ OU T _AC

C13

4.7␮F

+

C OM _ OU T

-

5.5k⍀

CPANEL

22nF

GND

The ADM8840 provides power up sequencing of the -15V

and +15V gate drive outputs, ensuring the -15V starts to

power up before the +15V.

The ADM8840 has a number of power save features, includ-

ing low power Shutdown. The 5.0V output consumes the

most power, so Power Efficiency is also maximised on this

output with an oscillator enabling scheme (Green IdleTM).

The ADM8840 is fabricated using CMOS technology for

minimal power consumption. The part is packaged in a 32-

pin LFCSP package.

TM Green Idle is a registered trademark of Analog Devices Inc.

REV. PrG 2/03

Information furnished by Analog Devices is believed to be accurate and

reliable. However, no responsibility is assumed by Analog Devices for its

use, nor for any infringements of patents or other rights of third parties

which may result from its use. No license is granted by implication or

otherwise under any patent or patent rights of Analog Devices.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

Analog Devices, Inc., 2003

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