LM1276 National Semiconductor Corporation, LM1276 Datasheet - Page 15

• Manufacturer Part Number: LM1276
• Description: 150 Mhz I2c Compatible Rgb Preamplifier With Internal 512 Character Osd Rom, 512 Character Ram And 4 Dacs
• Manufacturer: National Semiconductor Corporation

Pin
No.
18
19
20
21
22
23
24
25
26
27
Pin Descriptions and Application Information
Analog Ground
DAC 3 Output
DAC 2 Output
DAC 1 Output
Green Output
Analog V
Blue Output
Red Output
Pin Name
CLAMP
ABL
CC
Schematic
15
(Continued)
DAC outputs for cathode cut-off adjustments and
brightness control. The DAC values are set
through the I
least 1kΩ should be connected in series with
these outputs for additional ESD protection.
Ground pin and power supply pin for the output
analog portion of the LM1276. Note the
recommended charge storage and high
frequency capacitors which should be as close to
pins 21 and 22 as possible.
These are the three video output pins. They are
intended to drive the LM2476 and LM246X
family of cathode drivers. Nominally, about 2V
peak to peak will produce 40V peak to peak of
cathode drive.
The Automatic Beam Limiter input is biased to
the desired beam current limit by R
and normally keeps D
the current resupplying the CRT capacitance
(averaged by C
begins to turn off and the voltage at pin 26
begins to drop. The LM1276 then lowers the
gain of the three video channels until the beam
current reaches an equilibrium value.
This pin accepts either TTL or CMOS logic
levels. This pin can also be internally connected
to the Horizontal sync pin. The internal switching
threshold is approximately one-half of V
external series resistor, R, of about 1k is
recommended to avoid overdriving the input
devices. In any event, R must be large enough
to prevent the voltage at pin 27 from going
higher than V
2
CC
C compatible bus. A resistor of at
ABL
or below GND.
Description
) exceeds this limit, then D
INT
forward biased. When
ABL
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and V
CC
. An
BB
INT