NSC Demonstration Board

Figures 11, 12 show routing and component placement on

the NSC LM2202/2412 demonstration board. The schematic

of the board is shown in

Figure 10. This board provides a

good example of a layout that can be used as a guide for

future layouts. Note the location of the following compo-

nents:

•

C47 -V

and ground pins. (

Figure 12)

•

C49 -V

ground. (

Figure 12)

•

C46 and C77 -V

and V

(

Figure 11)

The routing of the LM2412A 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 LM2412A 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,

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 LM2412A 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 LM2412A 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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