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LM2940-N: my mail address for correspondence is

Part Number: LM2940-N

We are using LM2940imp-5 regulator in our circuit to generate 5V to the board with an input voltage of 24 V. The load current on regulator is 500mA. we are facing issue that when we increase input voltage beyond 12 V the out put voltage is decreasing from 5V with an load of 500 mA. with out load the out put is stable.

  • HI Srinivasa,

    You are likely running into thermal shutdown. I am not sure which package you are using, but to estimate the thermal rise based on power dissipation, you can use TJA from the following table:

    TJA is based on a Jedec Standard HIgh-K board as clarified in note #2 above. .

    So assuming a TO-220 package is being used, TJA is 23.3C/W. Therefore even at 12V on VIN and 5V at VOUT, with 500mA of power dissipation, this is a 7V drop so the power is 3.5W (7V*0.5A). So the thermal rise above the PCB ambient would be 3.5W*23.3 or 81.55C. If the PCB ambient in this case is 40C, this means the die temperature would be 81.55+40=121.55C.

    You can confirm thermal shutdown is actually engaging by using an oscilloscope to monitor VOUT. With a portable Voltage Meter, it would look like the average voltage is falling.

    Does this answer your question?