OBSOLETE

LM2476

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SNOSAH7B – JANUARY 2004 – REVISED APRIL 2013

PC BOARD LAYOUT CONSIDERATIONS

For optimum performance, use single-point grounds systems with adequate ground planes, isolate between

channels, apply good supply bypassing, and minimize unwanted feedback and parasitic capacitance. Also, the

length of the video signal traces from the preamplifier to the LM2476 and from the LM2476 to the CRT cathodes

should be as short as possible. The following references are recommended:

Ott, Henry W., “Noise Reduction Techniques in Electronic Systems”, John Wiley & Sons, New York, 1976.

“Video Amplifier Design for Computer Monitors”, TI Application Note 1013.

Pease, Robert A., “Troubleshooting Analog Circuits”, Butterworth-Heinemann, 1991.

Because of its high small signal bandwidth, the part may oscillate in a monitor if feedback occurs around the

video channel through the chassis wiring. To prevent this, leads to the video amplifier input circuit should be

shielded, and input circuit wiring should be spaced as far as possible from output circuit wiring.

TI DEMONSTRATION BOARD

Figure 13 is the schematic for the TI LM1276/3X/4X_2476 Demonstration PCB that can be used to evaluate the

LM1276, LM123X, or LM124X preamp with the LM2476 in a monitor. Figure 14 shows the routing and

component placement on the TI Demonstration PCB. 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:

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•

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arc protection.

The routing of the LM2476 driver outputs to the CRT is very critical to achieving optimum performance. Figure 15

shows the routing and component placement from Pin 17 of the LM2476 to the Red cathode. Note that the

components are placed so that they almost line up from the output pin of the LM2476 to the Red cathode pin of

the CRT connector. This is done to minimize the length of the video path between these two components for

optimal performance and to minimize EMI. Note also that L4, D9, D13 and R23, R19, D10 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 D13 is connected

directly to a section of the ground trace that has a short and direct path to CRT ground to shunt arcover current

Figure 15) which is connected to the same section of the ground trace as D13. The diode placement and routing

is very important for minimizing the voltage stress on the LM2476 during an arcover event. R37 and C29 are

placed very close to the clamp output on Pin 11. These components will help limit the current and voltage stress

to the clamp output. Lastly, notice that S2 is placed very close to the Red cathode and is connected directly to

CRT ground.

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Product Folder Links: LM2476