LM2412 National Semiconductor, LM2412 Datasheet - Page 6

• Manufacturer Part Number: LM2412
• Description: Monolithic Triple 2.8 ns CRT Driver
• Manufacturer: National Semiconductor

www.national.com
Application Hints
The routing of the LM2412 outputs to the CRT is very critical
to achieving optimum performance. Figure 13 shows the
routing and component placement from pin 1 to the blue
cathode. Note that the components are placed so that they
almost line up from the output pin of the LM2412 to the blue
cathode pin of the CRT connector. This is done to minimize
the length of the video path between these two components.
The direct video path is shown in by a dark gray line through
the components and the PCB traces. Note also that D24,
• C46 and C77 - V
V
ure 11 )
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clamp diodes. Very important for arc protection. ( Fig-
CC
bypass capacitors, near LM2412 and
(Continued)
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D25, R58 and D19 are placed to keep the size of the video
nodes to a minimum (R58 is located under D19). This mini-
mizes parasitic capacitance in the video path and also en-
hances the effectiveness of the protection diodes. The traces
in the video nodes to these components are shown by the
white line. The anode of protection diode D25 is connected
directly to the ground plane giving a short and direct path to
the LM2412 ground pins. The cathode of D24 is connected
to V
which is connected to the same section of the ground plane
as D25. The diode placement and routing is very important
for minimizing the voltage stress on the LM2412 during an
arc-over event. Lastly, notice that S3 is placed very close to
the blue cathode and is tied directly to CRT ground.
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very close to decoupling capacitor C78 ( Figure 13 )