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UCC2895: On/off operation

Phil Silverstein
Prodigy 30 points
Part Number: UCC2895

We are having a strange issue with the UCC2895 controller.

The problem we have is that when we turn the supply OFF and then back ON again the main power does not come up. The power factor correction section seems to be working, using an FA5502, and the auxiliary outputs are OK. Main switching, it appears, is inoperable. After an excessively long time measured in minutes, it eventually starts up again.

Note that this anomaly does not always appear. Sometimes the supply just acts normally.

My suspicion for this is that the problem is not of a transient nature, such as would occur with some kind of glitch, but is solid when it occurs such as would happen with a stable type device such as a F/F.

I have tried to submit this issue twice in the past and have two different case numbers, one of which (ending in 449) is closed and the other (ending in 360) is still open. I was asked to submit a schematic, and I am now authorized to do so. I have attached the schematic to the open case number (the one ending in 360). For reasons of confidentiality I cannot post the schematic publicly, sorry.

  • 0
    TI__Mastermind 25570 points

    Hello Phil

    I'm afraid I don't recognise the case numbers you quote - could you send me a link to them please - you can send them to me directly at  colingillmor@ti.com and please attach the schematic too.

    In the absence of any other information, here is a list of a few things which might be preventing the device from starting -

    If the VCC rail does not reach the UCLO_on threshold - typically 11V, then the device will not start switching.

    Please check the voltage at the SS pin - is it clamped to zero and starts to climb immediately prior to switching or does it climb normally as VCC is applied ?

    The REF pin should go to 5V immediately the VCC passes the UVLO_on threshold - does it do so or does it wait until just prior to switching starting.

    My apologies if this has already been covered.  Please note that I'm going to be out of the office until next Tuesday 26th but if you can get a response to me as soon as you get into the office I may have time to respond today.

    Regards
    Colin

  • 0 in reply to Colin Gillmor
    TI__Mastermind 25570 points

    Hello Phil

    Do you have any update ?  -  Please note that I'm going to be out of the office all next week.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    TI__Expert 3050 points

    Hi Phil,

    it is long time you have no reply. I am going close this thread now. if you have more question, you can create new thread to discuss.

    thanks