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UCC3813-5 failures

Other Parts Discussed in Thread: UCC3813-5, UCC3805

I have been experiencing  UCC3813-5 failures in a sepic dc/dc converter so I decided to power the UCC3813 with an 8 volt power supply (through a 250 ohm resistor). The loop was opened so current sense and feedback inputs are essentially grounded. The output is a 180kHz squarewave, as expected. After about 2 minutes the REF output starts creeping from 4v to about 7v and the oscillator stops and the output locks high or low. After a 5 minute rest the same behavior will repeat.  What could cause several of these parts to behave like this? I am careful about static and soldering procedures and am using a good bench power supply. I am also running out of UCC3813s.

  • I very carefully replaced the UCC3813-5 one more time, observing all the precautions not to damage it. After a few minutes the REF pin went to 7vdc and the oscillator stopped.

    I tried adding load resistors on the REF output to keep it from going above 4vdc. It helped but eventually still goes to 5.5vdc or so and the oscillator stops.

    The TI help line sent me to this forum to resolve this problem - I think I have bad chips or the chip design is bad. I am getting some UCC3805 samples that hopefully won't have this flaw.