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UCC28950: THERMAL SHUTDOWN

Eddie Loy
Intellectual 850 points
Part Number: UCC28950

SIRS,

I HAVE A UCC28950  WHICH AFTER THE RAIL VOLTAGE IS APPLIED (so far various stages between 20 vdc to 80 vdc) AFTER ABOUT 6-8 MINUTES OF RUN TIME THE SIGNALS WILL COMPLETELY SHUT DOWN.  THEN AFTER ABOUT 5-10 MINUTES OF BEING POWERED OFF AND AGAIN POWERED UP THE OUTPUT SIGNALS  ARE BACK, THEN THIS CYCLE WILL HAPPEN AGAIN.

I AM AT WITS END TRYING TO FIGURE THIS OUT, BUT i KEEP COMING BACK TO THERMAL SHUTDOWN.

PLEASE EXPLAIN THERMAL SHUTDOWN, HOW TO RECOGNIZE IT, POSSIBLE SOLUTIONS AND ANY INFORMATION OR LITERATURE THAT WILL HELP ME UNDERSTAND IT.

THE UCC28950 LITERATURE HAS NO INFORMATION ON THERMAL SHUTDOWN EXCEPT THE FOLLOWING: (BOTTOM OF PAGE SEVEN.

THANK YOU FOR YOUR ASSISTANCE.

  • 0
    TI__Mastermind 25570 points

    Hello Eddie

    There are a couple of possibilities other than Thermal Shutdown for the behaviour you mention.

    1/ VDD UVLO - check the VDD rail to the controller. The UVLO level for this device is at 6.7V Typ.

    2/ An overload condition causing the system to go into Hiccup mode. (Recovery from Hiccup mode requires that the SS/EN pin falls below 550mV and this can be prevented by a pull up resistor to VREF). Anyhow, monitor the CS and SS/EN pins carefully. Look at how the SS/EN pin behaves in the few seconds before the shutdown also look at the CS pin. If SS/EN drops immediately to 0V and CS+Slope_Comp is less than 2V peak  then that could be Thermal Shutdown, if it collapses relatively slowly and CS+Slope_COMP is at 2V (over a few hundred ms) then that is more like an overload condition. You will need to calculate the value of the slope compensation ramp set by the RSUM resistor because the Cycle-by-Cycle comparator compares the CS+Slope_Comp ramp to a fixed 2V level.

    3/ It could be thermal shutdown - don't risk your finger because the thermal shutdown level is about 160C. See if the device recovers immediately if you use some freezer spray to cool it.

    The device is unlikely to generate enough heat to self-heat to 160C so take a look for any heat sources close to it.

    Let us know how you get on -

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    Intellectual 850 points

    Thank you Collin for your response.

    I eill get back to you roughly Monday next week.

    Have a great weekend.

    Eddie Loy