OBSOLETE

LM2460

www.ti.com

SNOSA92B – JUNE 2002 – REVISED APRIL 2013

THERMAL CONSIDERATIONS

Figure 5 shows the performance of the LM2460 in the test circuit shown in Figure 3 as a function of case

temperature. The figure shows that the rise time of the LM2460 increases by approximately 13% as the case

temperature increases from 30°C to 100°C. This corresponds to a speed degradation of 2.0% for every 10°C rise

in case of temperature. The fall time has almost no change as the case temperature increases.

Figure 7 shows the maximum power dissipation of the LM2460 vs Frequency when all three channels of the

active time (device operating at the specified frequency) which is typical in a monitor application. The other 28%

of the time the device is assumed to be sitting at the black level (105V in this case). This graph gives the

designer the information needed to determine the heat sink requirement for his application. The designer should

note that if the load capacitance is increased the AC component of the total power dissipation would also

increase.

The LM2460 case temperature must be maintained below 100°C. If the maximum expected ambient temperature

is 70°C and the maximum power dissipation is 11W (from Figure 7, 70 MHz bandwidth) then a maximum heat

sink thermal resistance can be calculated:

(1)

This example assumes a capacitive load of 8 pF and no resistive load.

TYPICAL APPLICATION

A typical application of the LM2460 is shown in Figure 11 and Figure 12. Used in conjunction with a LM1267 pre-

amp and a LM2479 bias clamp, a complete video channel from monitor input to CRT cathode can be achieved.

Performance is ideal for 1024 x 768 resolution displays with pixel clock frequencies up to 80 MHz. Figure 11 and

Figure 12 are the schematic for the TI demonstration board that can be used to evaluate the LM1267/2460/2479

combination in a monitor.

PC BOARD LAYOUT CONSIDERATIONS

For optimum performance, an adequate ground plane, isolation between channels, good supply bypassing and

minimizing unwanted feedback are necessary. Also, the length of the signal traces from the preamplifier to the

LM2460 and from the LM2460 to the CRT cathode 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”, Texas Instruments 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 shows the routing and component placement on the TI LM126X/246X/LM2479/80 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:

•

•

•

protection.

The routing of the LM2460 outputs to the CRT is very critical to achieving optimum performance. Figure 14

shows the routing and component placement from pin 3 of the LM2460 to the blue cathode. The blue video path

from the LM2460 output is shown by the darker traces. Note that the components are placed so that they almost

line up from the output pin of the LM2460 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

Copyright © 2002–2013, Texas Instruments Incorporated

Submit Documentation Feedback

7

Product Folder Links: LM2460