NSC DEMONSTRATION BOARD

Figure 12 shows the routing and component placement on

the NSC LM126X/246X/LM2479/80 demonstration board.

The schematic of the board is shown in

Figure 10 and Figure

11. 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:

•

C16, C19 — V

pin 4 and ground pins

•

C17, C20 — V

and ground

•

C46, C47, C48 — V

and V

The routing of the LM2465 outputs to the CRT is very critical

to achieving optimum performance.

Figure 13 shows the

routing and component placement from pin 3 of the LM2465

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

that they almost line up from the output pin of the LM2465 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

attached 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 LM2465 ground pins. The

cathode of D9 is connected to V

capacitor C48 (see

Figure 13) 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 LM2465 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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