LM1237 National Semiconductor Corporation, LM1237 Datasheet - Page 11

• Manufacturer Part Number: LM1237
• Description: 150 Mhz I2c Compatible Rgb Preamplifier With Internal 254 Character Osd And 4 Dacs
• Manufacturer: National Semiconductor Corporation

Pin Descriptions and Application Information
Pin
No.
22
23
24
Pin Name
H Flyback
CLAMP
ABL
Schematic
11
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 LM1237 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
to avoid overdriving the input devices. In any
event, R
voltage at pin 23 from going higher than V
below GND.
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 300 ohms 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)
EXT
must be large enough to prevent the
ABL
31
Description
) exceeds this limit, then D
, of about 1k is recommended
INT
17
forward biased. When
H
is usually needed for
CC
C
17
. An external
significantly
34
ABL
and C
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and V
CC
8
18
H
BB
are
INT
or