NSC DEMONSTRATION BOARD

Figure 13 shows the routing and component placement on

the NSC LM126X/2421 demonstration board. The schematic

of the board is shown in

Figure 11 and Figure 12. 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

components:

•

C19—V

and ground pins

•

C20—V

and ground

•

C46, C47, C48 — V

and V

The routing of the LM2421 outputs to the CRT is very critical

to achieving optimum performance.

Figure 14 shows the

routing and component placement from pin 1 of the LM2421

to the blue cathode. Note that the components are placed so

that they almost line up from the output pin of the LM2421 to

the blue cathode pin of the CRT connector. This is done to

minimize the length of the video path between these two

components. Note also that D8, D9, R24 and D6 are placed

to minimize the size of the video nodes that they are at-

tached to. This minimizes parasitic capacitance in the video

path and also enhances the effectiveness of the protection

diodes. The anode of protection diode D8 is connected

directly to a section of the the ground plane that has a short

and direct path to the LM2421 ground pins. The cathode of

D9 is connected to V

C48 (see

Figure 14) which is connected to the same section

of the ground plane as D8. The diode placement and routing

is very important for minimizing the voltage stress on the

LM2421 during an arcover event. Lastly, notice that S3 is

placed very close to the blue cathode and is tied directly to

CRT ground.

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