LM1269 datasheet(12/20 Pages) NSC

12 / 20 page

Functional Description (Continued)

H Flyback: H Flyback is an analog signal input from the

monitor horizontal scan. The “H Blank” section uses this

signal to add horizontal blanking to the output video signal.

This enables the user to blank at the cathodes during hori-

zontal flyback. An optional capacitor and/or resistor to

ground may be needed if noise interferes with the H Flyback

signal.

This feature gives very accurate timing for the horizontal

blanking; however, the flyback signal must be very clean.

There should be no ringing or other noise on the flyback

signal.

LIMIT is used to limit the input current into the IC to a typical

value of+1mA during flyback and −100 µA during normal

forward scan. For example if an H flyback with a peak of

100V is used, R

LIMIT = 100 kΩ. The internal input impedance

of pin 24 is low to limit the maximum voltage swing at the

input to within the supply rail and ground. The IC interface

circuit creates a digital signal from this waveform, which is

used as the blanking signal at the “Output Buffer Amp”. This

signal adds blanking to the video output signal.

Figure 5

shows the H flyback waveforms and the location of R

LIMIT.A

56 pF capacitor has been added to the H Flyback pin on the

demo board for filtering noise on the H Flyback signal.

H Blank: Some customers may still prefer to use a standard

logic signal for the horizontal blanking. Pin 24 can be

adapted to accept a logic input. It is necessary for the current

flow into pin 24 to reverse for proper operation. Therefore the

logic signal must be AC coupled into pin 24.

Figure 6 shows

the recommended circuit for a logic signal input. The blank

signal must be a positive pulse.

Power Save Mode: There are two modes of power save:

Blanking the video

Turning off most of the power for maximum power sav-

ings.

In the first mode the video is completely blanked. By setting

bit-0 in register 9 to a 1 the video will be completely blanked.

This gives some power savings since there is no beam

current in the monitor. Maximum power saving is obtained in

the second mode. Bits 0 and 1 in register 9 should be set to

a 1. Bit 1 in register 9 turns off the video output stage of the

DS200099-26

FIGURE 4. ABL

DS200099-27

FIGURE 5. H Flyback Input Pulse

DS200099-28

FIGURE 6. Standard Logic H Blank

LM1269 Datasheet(PDF) 12 Page - National Semiconductor (TI)

LM1269 Datasheet(HTML) 12 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL