MAX1881 查看數據表（PDF） - Maxim Integrated

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MAX1881

Quad-Output TFT LCD DC-DC Converters with Buffer

Maxim Integrated 

Quad-Output TFT LCD DC-DC

Converters with Buffer

INPUT

VIN = 3.3V CIN

4.7µF

RRDY

100kΩ

TO LOGIC

LDO

VLDOOUT = 5V CLDO

4.7µF

C1

0.22µF

MAIN

(8V)

R8

49.9kΩ

L1

6.8µH

IN

SHDN

RDY

SUPL

LDOOUT

R7

150kΩ

MAX1778

C2

0.1µF

FBL

DRVN

LX

FB

SUPB

SUPN

SUPP

DRVP

NEGATIVE

VNEG = -5V C3

1.0µF

R5

200kΩ

R6

49.9kΩ

CREF

0.22µF

FBN

FBP

REF

INTG

FLTSET

PGND

BUFOUT

BUF-

BUF+

GND

TGND

R2

274kΩ

R2

49.9kΩ

C4

0.1µF

C4

0.1µF

R3

750kΩ

R4

49.9kΩ

CBUF

1.0µF

MAIN

COUT VMAIN = 8V

(2) 4.7µF

C5

1.0µF

C7

1.0µF

POSITIVE

VPOS = 20V

BUFFER OUTPUT

VBUFOUT = VSUPB/2

Figure 1. Typical Application Circuit

Detailed Description

The MAX1778/MAX1880–MAX1885 are highly efficient

multiple-output power supplies for thin-film transistor

(TFT) liquid crystal display (LCD) applications. The

devices contain one high-power step-up converter, two

low-power charge pumps, an operational transconduc-

tance amplifier (VCOM buffer), and a low-dropout linear

regulator. The primary step-up converter uses an inter-

nal N-channel MOSFET to provide maximum efficiency

and to minimize the number of external components.

The output voltage of the main step-up converter

(VMAIN) can be set from VIN to 13V with external resis-

tors.

The dual charge pumps (MAX1778/MAX1880/

MAX1881/MAX1882 only) independently regulate a

positive output (VPOS) and a negative output (VNEG).

These low-power outputs use external diode and

capacitor stages (as many stages as required) to regu-

late output voltages from -40V to +40V. A unique

control scheme minimizes output ripple as well as

capacitor sizes for both charge pumps.

A resistor-programmable 40mA linear regulator

(MAX1778/MAX1881/MAX1883/MAX1884 only) can

provide preregulation or postregulation for any of the

supplies. For higher current applications, an external

transistor can be added.

Additionally, the VCOM buffer provides a high current

output that is ideal for driving capacitive loads, such as

the backplane of a TFT LCD panel. The positive feed-

back input features dual mode operation, allowing this

input to be connected to an internal 50% resistive-

divider between the buffer’s supply voltage and

ground, or externally adjusted for other voltages.

Also included in the MAX1778/MAX1880–MAX1885 is a

precision 1.25V reference that sources up to 50µA,

logic shutdown, soft-start, power-up sequencing,

adjustable fault detection, thermal shutdown, and an

active-low, open-drain ready output.

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