Rainbow-electronics MAX1885 Bedienungsanleitung PDF herunterladen (Seite 19)

MAX1778/MAX1880–MAX1885

Quad-Output TFT LCD DC-DC

Converters with Buffer

______________________________________________________________________________________ 19

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 (V

COM

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

MAIN

) can be set from V

to 13V with external resis-

tors.

The dual charge pumps (MAX1778/MAX1880/

MAX1881/MAX1882 only) independently regulate a

positive output (V

POS

) and a negative output (V

NEG

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 V

COM

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.

BUFFER OUTPUT

BUFOUT

= V

SUPB

POSITIVE

POS

= 20V

BUF

1.0µF

LDO

4.7µF

REF

0.22µF

1.0µF

0.1µF

6.8µH

0.1µF

0.22µF

4.7µF

SHDN

RDY

SUPL

LDOOUT

SUPN

SUPP

DRVP

FBP

750kΩ

200kΩ

150kΩ

49.9kΩ

274kΩ

INPUT

= 3.3V

LDO

LDOOUT

= 5V

NEGATIVE

NEG

= -5V

TO LOGIC

BUFOUT

BUF-

BUF+

GND

TGND

FBL

DRVN

FBN

REF

FLTSET

INTG

PGND

SUPB

MAX1778

MAIN

= 8V

MAIN

(8V)

OUT

(2) 4.7µF

1.0µF

RDY

100kΩ

Figure 1. Typical Application Circuit

1 2 ... 14 15 16 17 18 19 20 21 22 23 24 ... 37 38

Kommentare zu diesen Handbüchern

Keine Kommentare

Rainbow-electronics MAX1885 Bedienungsanleitung Seite 19

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Sensoren Rainbow-electronics MAX1885