LM1229YA datasheet(13/27 Pages) NSC

13 / 27 page

Application Information (Continued)

No.

Pin Name

Schematic

Description

HOSC2

HOSC1

The oscillator can be a standard 12 MHz

ceramic or crystal oscillator. Two suitable

manufacturer’s part numbers are Murata

CST12.0MT and Panasonic PX1200MC-ND.

XRAY

This pin provides X-ray sense and shutdown.

The input is a rectified horizontal flyback pulse.

B is adjusted to cause shutdown at the desired

amplitude of the flyback pulse. This provides

X-ray protection by turning off the horizontal

drive. After the shutdown, the LM1229 will be

reset when V

CC drops below 4V or when the

HDRIVE output is disabled and reenabled with

bit 5 of the HEHT register. This shutdown

function can be disabled by setting bit 6 of the

HEHT register to a 1.

HSYNC

VSYNC

These are the horizontal and vertical sync inputs

to the LM1229. The horizontal sync is required

by the horizontal PLL and the horizontal blanking

function. The vertical sync is required by the

vertical blanking function which includes the

programmable vertical blanking output pulse and

the RGB vertical blanking. These are both 5V

logic levels with thresholds as given in the

specifications section. Care must be taken to

prevent sync overshoots from reaching the

LM1229.

DAC 3 Output

DAC 2 Output

DAC 1 Output

These are the DAC outputs for the RGB cathode

cut-off adjustments. The DAC output levels are

set through the I

2C compatible bus. These can

be set for 4.2V or 2.1V full scale to match the

various NSC bias ICs.

NSC’s CRT arcing tests and experience shows

that the best output termination for the DAC

outputs is a 0.1 µF capacitor to ground at the IC

terminals and a series 1k resistor close to the

load.

VBLANK

OUT

This is a positive going logic pulse which can be

used for vertical blanking on G1. It can be an

input to the LM2485 where it is amplified to

either 20V or 40V negative going peak to peak,

depending on an option pin. The pulse starts

when an input is received on the Vertical Flyback

Input on pin 62 and lasts for the number of scan

lines loaded in the VBLANK register, 0x51[7:0].

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