LM1270NA datasheet(7/27 Pages) NSC

7 / 27 page

Pin Descriptions (Continued)

No.

Pin Name

Schematic

Description

Ground

Ground pin for the output analog portion of the

LM1270 circuitry, and power supply pin for all the

analog of the LM1270. Note the recommended

charge storage and high frequency capacitors which

should be as close to pins 17 and 18 as possible.

Green Video Out

Red Video Out

Blue Video Out

Video outputs of the LM1270. Typically the output is

set to 0.7 V

P-P to drive any standard video pre-amp.

When Hi-Brite is activated the user can set the

video output as high as 1.0 V

P-P.

REF Cap

Provides filtering for the internal voltage which sets

the internal bias current in conjunction with R

EXT.A

minimum of 0.1 µF is recommended for proper

filtering. This capacitor should be placed as close to

pin 22 and the analog ground return as possible.

This pin can also be set to use an external V

REF.

REFREXT

Sets the internal current sources through a

10 k

Ω 1% external resistor. Resistor value and

accuracy is critical for optimum operation of the

LM1270. This resistor should be placed as close to

pin 23 and the analog ground return as possible.

Clamp

This pin can either accept an external clamp pulse

or send an internally generated clamp pulse to the

video circuits. As an input this pin accepts either

TTL or CMOS logic levels. The internal switching

threshold is approximately one-half of V

CC.An

external series resistor, R

CLP, of about 1 k

Ω is

recommended to avoid overdriving the input

devices, or for current limiting the drivers if being

used as an output. C

CLP may be necessary for

filtering noise on the clamp input. R

LOAD should be

used if this pin is an output with a value of about

10 k

Ω.

LM1270NA Datasheet(PDF) 7 Page - National Semiconductor (TI)

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