OBSOLETE

LM2436

www.ti.com

SNOSA13B – JUNE 2002 – REVISED APRIL 2013

½W solid carbon type resistor. R1 can be a ¼W metal or carbon film type resistor. Having large value resistors

for R1 and R2 would be desirable, but this has the effect of increasing rise and fall times. Inductor L1 is critical to

reduce the initial high frequency voltage levels that the LM2436 would be subjected to. The inductor will not only

help protect the device but it will also help minimize rise and fall times as well as minimize EMI. For proper arc

protection, it is important to not omit any of the arc protection components shown in Figure 9.

Figure 9. One Channel of the LM2436 with the Recommended Application Circuit

Optimizing Transient Response

Referring to Figure 9, 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 # 78FR56M) were used for optimizing the performance of the device in the TI

application board. The values shown in Figure 9 can be used as a good starting point for the evaluation of the

LM2436. The TI demo board also has a position open to add a resistor in parallel with L1. This resistor can be

used to help control overshoot. Using variable resistors for R1 and the parallel resistor will simplify finding the

values needed for optimum performance in a given application. Once the optimum values are determined the

variable resistors can be replaced with fixed values.

Effect of Load Capacitance

Figure 8 shows the effect of increased load capacitance on the speed of the device. This demonstrates the

importance of knowing the load capacitance in the application.

Effect of Offset

Figure 7 shows the variation in rise and fall times when the output offset of the device is varied from 40 to 50

time shows a variation less than 4% relative to the center data point.

Thermal Considerations

Figure 4 shows the performance of the LM2436 in the test circuit shown in Figure 2 as a function of case

temperature. The figure shows that the rise time of the LM2436 increases by approximately 8% as the case

temperature increases from 40°C to 100°C. This corresponds to a speed degradation of 1.3% for every 10°C rise

in case temperature.The fall time increases by approximately 4% as the case temperature increases from 40°C

to 100°C.

Figure 6 shows the maximum power dissipation of the LM2436 vs. Frequency when all three channels of the

72% 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 (65V 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 will also increase.

Copyright © 2002–2013, Texas Instruments Incorporated

Submit Documentation Feedback

7

Product Folder Links: LM2436