OBSOLETE

LM2432

www.ti.com

SNOSAL4E – MARCH 2005 – REVISED APRIL 2013

A HDTV signal generator pattern that yields a practical worst-case picture condition is a “multi-burst” pattern that

consists of a 1-to-30 MHz sine wave sweep over each of the active lines. The power dissipated by the LM2432

as a result of this picture condition can be approximated by taking the average of the power between 1 to 30

MHz in Figure 10. This average is 7W. Because a square wave input was used to generate this power curve, a

sine wave would cause the LM2432 to dissipate slightly less power, probably about 6.7W. This is one common

way to determine a practical figure for maximum power dissipation. It is the system designer's responsibility to

establish the worst-case picture condition for his particular application and measure dissipation under that

condition to choose a proper heatsink.

Heatsink Calculation Example

Once the maximum dissipation is known, Figure 11 can be used to determine the heatsink requirement for the

LM2432. If the 1-to-30 MHz multi-burst test described previously is assumed to be worst-case picture condition

that yields maximum dissipation, then the LM2432 will dissipate about 6.7W. The power derating curve shows

that the maximum allowed case temperature is 120°C when 6.7W is dissipated. If the maximum expected

ambient temperature is 65°C, then the maximum thermal resistance from device case-to-sink (

calculated:

(1)

(2)

This example assumes a capacitive load of 10 pF and no resistive load. The designer should note that if output

power dissipation will also increase.

Tips for Reducing Power Dissipation

The following methods can be used to reduce the power dissipated by the LM2432 in order to optimize heatsink

size and cost:

•

adjustments.

•

Reduce the input bandwidth to the LM2432 while maintaining acceptable picture performance.

•

•

Minimize capacitive load on the LM2432 output by using good PCB layout practices.

OPTIMIZING TRANSIENT RESPONSE

Referring to Figure 13, there are three components (R1, R2 and L1) that can be adjusted to optimize the

transient response of the application circuit. Increasing the values of R1 and R2 will slow the circuit down while

decreasing overshoot. Increasing the value of L1 will speed up the circuit as well as increase overshoot. It is very

important to use inductors with very high self-resonant frequencies, preferably above 300 MHz. Ferrite core

inductors from J.W. Miller Magnetics (part # 78FR_ _k) were used for optimizing the performance of the device in

the TI application board. The values shown in Figure 16 can be used as a good starting point for the evaluation

of the LM2432. Using a variable resistor for R1 will simplify finding the value needed for optimum performance in

a given application. Once the optimum value is determined, the variable resistor can be replaced with a fixed

value.

that provides input speeds with 12 ns rise and fall times.

NOTE

The RGB processor's sharpness feature adds emphasis (preshoots and overshoots) to the

rising and falling edges of the input pulse, which consequently adds emphasis to the

cathode pulse response.

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Product Folder Links: LM2432