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LM1238 Datasheet(PDF) 10 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
Part No. LM1238
Description  110 MHz I2C Compatible RGB Preamplifier with Internal Simple OSD Generator and 4 DACs
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Maker  NSC [National Semiconductor (TI)]
Homepage  http://www.national.com
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LM1238 Datasheet(HTML) 10 Page - National Semiconductor (TI)

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Pin Descriptions and Application Information (Continued)
Pin
No.
Pin Name
Schematic
Description
22
ABL
The Automatic Beam Limiter input is biased to
the desired beam current limit by R
ABL and VBB
and normally keeps D
INT forward biased. When
the current resupplying the CRT capacitance
(averaged by C
ABL) exceeds this limit, then DINT
begins to turn off and the voltage at pin 22
begins to drop. The LM1238 then lowers the
gain of the three video channels until the beam
current reaches an equilibrium value.
23
CLAMP
This pin accepts either TTL or CMOS logic
levels. The internal switching threshold is
approximately one-half of V
CC. An external
series resistor, R
31, of about 1k is recommended
to avoid overdriving the input devices. In any
event, R
EXT must be large enough to prevent the
voltage at pin 23 from going higher than V
CC or
below GND.
24
H Flyback
Proper operation requires current reversal. R
H
should be large enough to limit the peak current
at pin 24 to about +4 ma during blanking, and
−500 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
34 and C8 are
typically 300 ohms and 330 pf when the flyback
waveform has ringing and needs filtering. C
18
may be needed to filter extraneous noise and
can be up to 100 pF.
www.national.com
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