LM1247 National Semiconductor, LM1247 Datasheet - Page 11

• Manufacturer Part Number: LM1247
• Description: 150 MHz I2C Compatible RGB Preamplifier with Internal 512 Character OSD ROM, 512 Character RAM and 4 DACs
• Manufacturer: National Semiconductor

Pin Descriptions and Application Information
Pin
No.
19
20
21
22
23
24
Green Output
Blue Output
Red Output
Pin Name
H Flyback
CLAMP
ABL
Schematic
11
These are the three video output pins. They are
intended to drive the 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 22
begins to drop. The LM1247 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. The internal switching threshold is
approximately one-half of V
series resistor, R
recommended to avoid overdriving the input
devices. In any event, R
enough to prevent the voltage at pin 23 from
going higher than V
Proper operation requires current reversal. R
should be large enough to limit the peak current
at pin 24 to about +4 ma during blanking, and
−500 µA during scan. C
logic level inputs and should be large enough to
make the time constant, R
larger than the horizontal period. R
typically 300Ω and 330 pF when the flyback
waveform has ringing and needs filtering. C
may be needed to filter extraneous noise and
can be up to 100 pF.
(Continued)
ABL
31
Description
) exceeds this limit, then D
, of about 1K is
CC
INT
or below GND.
17
EXT
forward biased. When
H
is usually needed for
CC
C
must be large
17
. An external
significantly
34
ABL
and C
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and V
8
18
H
BB
are
INT