LM1237 National Semiconductor Corporation, LM1237 Datasheet - Page 9

• 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.
10
1
2
3
4
5
6
7
8
V
Analog Ground
Green Video In
REF
Digital Ground
Blue Video In
V
Red Video In
Pin Name
REF
V Flyback
PLL V
Current Set
Bypass
CC
Schematic
9
Required for OSD synchronization and is also
used for vertical blanking of the video outputs.
The actual switching threshold is about 35% of
V
but for flyback inputs, an AC coupled
differentiator is recommended, where R
enough to prevent the voltage at pin 1 from
exceeding V
be small enough to flatten the vertical rate ramp
at pin 1. C
Provides filtering for the internal voltage which
sets the internal bias current in conjunction with
R
proper filtering. This capacitor should be placed
as close to pin 2 and the pin 4 ground return as
possible.
External resistor, 10k 1%, sets the internal bias
current level for optimum performance of the
LM1237. This resistor should be placed as close
to pin 3 and the pin 4 ground return as possible.
This is the ground for the input analog portions
of the LM1237 internal circuitry.
These video inputs must be AC coupled with a
.0047 µF cap. Internal DC restoration is done at
these inputs. A series resistor of about 33Ω and
external ESD protection diodes should also be
used for protection from ESD damage.
The ground pin should be connected to the rest
of the circuit ground by a short but independent
PCB trace to prevent contamination by
extraneous signals. The V
isolated from the rest of the V
bead and bypassed to pin 8 with an electrolytic
capacitor and a high frequency ceramic.
CC
EXT
. For logic level inputs C
. A minimum of 0.1 µF is recommended for
24
CC
may be needed to reduce noise.
or going below GND. C
Description
CC
4
pin should be
CC
can be a jumper,
line by a ferrite
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4
V
should
is large