LM2457

Monolithic Triple 7.5nS CRT Driver With Integrated

Clamp and G1 Blanking

General Description

The LM2457 driver is an integrated high voltage triple CRT

driver circuit designed for use in color monitor applications.

The input signal interface to the IC is a multiplexed signal

containing both clamp and video signal information, relative

to an external 1.7 VDC reference.

The IC contains three high gain, differential input, high input

impedance, wide band amplifiers which directly drive the

RGB cathodes of a CRT. Each channel has its gain internally

set to -52 and can drive CRT capacitive loads as well as

resistive loads present in other applications, limited only by

the package’s power dissipation.

Integrated with the driver is a triple video clamp circuit for DC

recovery of each of the AC coupled video outputs. The DC

clamp circuit amplifies the clamp signal that is multiplexed on

the video signal input. The DC clamp amplifiers are high

gain, differential input, high input impedance amplifiers, set-

ting a low impedance DC level at the clamp output which can

be used to restore the DC level of the cathode drive. Each

channel has a gain that is internally set to +75.

Also integrated within the package is a 43V

ing driver that is designed to drive the vertical retrace blank-

ing signal to the G1. This is a current limited, low impedance

output capable of driving normal G1 decoupling capaci-

tances via an external resistor.

The output of the G1 driver can also be used to drive a

voltage boost capacitor (22uF). When connected between

the G1 drive output and the 120v supply input pin, a 120v

boost supply is achieved which can be used to drive the

internal DC clamp circuit, thereby eliminating the require-

ment for a 120V clamp supply.

The IC is packaged in an industry standard 15 lead TO-220

molded plastic power package.

Features

n

7.5ns low power driver

n

Three integrated active clamp circuits

n

Integrated 120V supply and G1 vertical blank drive

circuit

n

Multiplexed signal interface to LM125X OSD Pre-amp

minimizes pin count while increasing functionality

n

External System voltage reference

n

Convenient TO-220 staggered lead package

Recommended Applications

n

1024 x 768 Resolution displays up to 85Hz refresh

n

Pixel clock frequencies up to 95MHz

n

Monitor requiring horizontal video blanking

Block Diagram

Package Pinout

DS101379-1

FIGURE 1. LM2457 Block Diagram

DS101379-2

FIGURE 2. LM2457 Package Pinout

Order Number LM2457TA

October 2000

© 2000 National Semiconductor Corporation

DS101379

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