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UC2825A-EP: Can this device draw high current at very high temperature

john pease1
Prodigy 20 points
Part Number: UC2825A-EP
Other Parts Discussed in Thread: UC2825A

My power converter shuts down  and draws very high current from its AUX supply. The UC2825A-EP draws about 50 mA at 10.5V at room temperature.  When I increase the board temperature

above 85C and allow a several minute soak time, my AUX supply current limits (>500 mA) and the power converter shuts down  for 10's of seconds then restarts for 10's of seconds. This cycle will repeat until I let the board cool down to about 70C where it will restart and stay running until I heat the board again above 85C.

There are other chips running off the AUX supply including an external gate driver. I cannot measure the UC2825A-EP Tj but with 0.5W dissipation, we can expect that we are close to the data sheet maximum 528 mW @ 85C.

Will the UC2825a-EP  draw high current at elevated temperature then draw the nominal current when it cools down?

I could not find a description of the thermal shut down behavior of this device.  Could you please describe what functions are disabled if there is a thermal shut down feature?

  • 0
    TI__Mastermind 34465 points

    Hello John,

    I think most likely the UC2825A is exceeding its max junction temperature rating in your application and causing the controller to shutdown.
    This part does not have an over temperature protection feature and I notice that there is very little thermal information available in the data sheet.
    A power dissipation of 0.5W in a 16 pin SOIC package sounds very high .

    I can request the thermal resistance data for this part and this will enable you to calculate the actual junction temperaturew in your application.
    Would you like me to do this ?

    Regards

    John

  • 0 in reply to John Griffin1
    Prodigy 20 points

    Hi John,

    Your part draws 50 mA at 10.5V with external gate drive. The data sheet says 36 mA max which is pretty close. You say that 0.5W is very high yet that is close to what the part is expected to dissipate.

    Please provide your reasons for saying that you think 0.5W is very high.

    Also please provide some details regarding the shut down behavior. V ref goes to zero, the oscillator stops, the outputs are inhibited, what? I cannot see any information about this in the data sheet.

    At what temperature is this shut down supposed to occur?

    Thank you

    John

  • 0 in reply to john pease1
    TI__Mastermind 34465 points

    John,

    The part is shutting down because your design is marginal and it is surprising that the part recovers
    That is all I can tell for sure from your sparse information.
    As I said my suspicion is that the part is exceeding its operating temperature limit.

    Best of luck with your troubleshooting.

    Regards

    John