LM1229 Datasheet, PDF (15/27 Pages) National Semiconductor (TI) – I2C Compatible CMOS TV RGB and Deflection Processor

Application Information (Continued)
Pin
Pin Name
No.
51
ABL
Schematic
53
V_REF R_EXT
57
Blue Output
58
Red Output
59
Green Output
62 Vertical Flyback
Description
The Automatic Beam Limiter input is biased to
the desired beam current limit by R_ABL and V_BB
and normally keeps D_INT and the 1N4148
forward biased. When the current resupplying
the CRT capacitance (averaged by C_ABL)
exceeds this limit, then D_INT and the 1N4148
begin to turn off and the voltage at pin 51 begins
to drop. The LM1229 then lowers the gain of the
three video channels until the beam current
reaches an equilibrium value. The 1N4148 is
needed to prevent overcurrent in D_INT in cases
where the ABL limit is greater than 1 mA.
External current set resistor, 10k 1%, sets the
internal bias current level for optimum
performance of the LM1229. This resistor should
be placed as close to pin 53 and the pin 52
ground return as possible.
These are the three video output pins. They are
intended to drive the National family of cathode
drivers. Nominally, about 2.8V peak to peak will
produce 140V peak to peak of cathode drive with
the LM2426.
This input is used to start the VBLANK output
pulse which is used internally for vertical
blanking of the RGB outputs. It is also used for
the V Protect function which blanks the RGB
video outputs if the vertical deflection fails. The
values of C_V and R_V should be chosen to
eliminate the long vertical rate slope at pin 62
and also ensure that this pin is not forced above
V_CC or below GND. The bias level at this pin is
about 25% of V_CC and the actual switching
threshold is about 35% of V_CC.
15
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