LM1253A National Semiconductor, LM1253A Datasheet - Page 8

• Manufacturer Part Number: LM1253A
• Description: Monolithic Triple 180 MHz I2C CRT Pre-amp With Integrated Analog On Screen Display (OSD) Generator
• Manufacturer: National Semiconductor

www.national.com
Test Settings
Pin Descriptions
Pin 1 — R
pin to set up the internal current sources. The LM1253A is
optimized for this value of resistor. A DC voltage only will be
on this pin. Decreasing the value of this resistor will increase
supply current while degrading performance; increasing the
value of the resistor will decrease supply current and also
degrade the performance. Do not place the resistor close to
sources of heat such as the CRT driver. Figure 29 shows the
components connected to pin 1, Figure 11 shows the internal
schematic of pin 1.
Pin 2 — V Blank Out This pin supplies a variable width,
negative going pulse at the vertical rate to the CRT Driver. V
Blank is triggered from the signal on pin 15, which comes
from the vertical flyback. The CRT Driver supplies the pull up
for this pin. The width of this pulse is set by the value in the
VBLANKDUR register (8403h). Figures 4, 5, 6 show the re-
sulting V Blank Out pulse with various values in register
8403h. The trace connecting pin 2 of the LM1253A to the
LM2453 must be kept away from the output circuitry of the
LM2453. Figure 29 shows the external schematic of pin 2,
Figure 12 shows the internal schematic of pin 2.
Contrast
R,G,B Gain
Brightness
R,G,B Bias
DC Offset
Pedestal Offset
Control
EXT
V
REF
FIGURE 4. V Blank = 10
A 10 k
1% resistor is connected to this
Bits
No.
of
7
7
8
8
3
3
DS101265-7
Setting 1
(Hex FF)
(Hex FF)
(Hex 7F)
(Hex 7F)
(Hex 07)
(Hex 07)
TABLE 1. Control Test Settings
Basic
Test
Max
Max
Max
Max
Max
Min
8
Setting 2
(Hex FF)
(Hex FF)
(Hex 7F)
(Hex 7F)
(Hex 00)
(Hex 07)
Pin 3 — V
pin to decouple V
nel circuits to make the VideoPlex signal. Figure 29 shows
the external schematic of pin 3, Figure 13 shows the internal
schematic of pin 3.
Pin 4, 5, 6 — Blue, Red, and Green Video In The red, blue,
and green video signal is AC coupled into these pins. The
value of the capacitors is very important as they also serve
Basic
Test
Max
Max
Max
Max
Max
Max
REF
Cap A 0.1 µF capacitor is placed close to this
FIGURE 6. V Blank = 127
FIGURE 5. V Blank = 63
REF
on all Channels
. V
Set for 1 V
Setting 3
REF
(Hex 7F)
(Hex 00)
(Hex 00)
(Hex 07)
(Hex 00)
Basic
Test
Max
Min
Min
Min
Min
is used by the three video chan-
P-P
DS101265-8
DS101265-9
Setting 4
(Hex 7F)
(Hex 7F)
(Hex 00)
(Hex 00)
(Hex 07)
(Hex 00)
Basic
Test
Max
Max
Min
Min
Min
Min