LM1270NA datasheet(6/27 Pages) NSC

6 / 27 page

Pin Descriptions (Continued)

No.

Pin Name

Schematic

Description

H Sync

Logic level horizontal sync signal received from the

video card in the PC or sync stripper circuit.

SCL

The I

2C compatible Clock line. A pull-up resistor of

about 2 k

Ω should be connected between this pin

and V

CC. A 100

Ω resistor should be connected in

series with the clock line for additional ESD

protection.

SDA

The I

2C compatible data line. A pull-up resistor of

about 2 k

Ω should be connected between this pin

and V

CC. A 100

Ω resistor should be connected in

series with the data line for additional ESD

protection.

Blank/Interrupt

Out

This output pin can be selected for Vertical Blank,

blank all the video, or no blanking. Provides the

blanking signal normally used at G1 of the CRT,

blanking the video during vertical retrace. If blanking

is not required, this pin may be used as an interrupt

signal for the microcontroller.

H Flyback

Proper operation requires current reversal. R

should be large enough to limit the peak current at

pin 16 to about +2 mA during blanking, and

−300 µA during scan. C

17 is usually needed for logic

level inputs and should be large enough to make

the time constant, R

HC17 significantly larger than the

horizontal period. R

Fil and CFil are typically 300

Ω

and 330 pF when the flyback waveform has ringing

and needs filtering. These two parts are not used on

the current neck board. C

57 may be needed to filter

extraneous noise and can be up to 100 pF.

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