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PMP7389 Reference design lock-up

Michael Deck
Prodigy 50 points
Other Parts Discussed in Thread: TPS2511, UCC28610

I am using the 5 AC/DC portion of the PMP7389 design in one of my designs. I have found that my design stops providing 5 volts sometimes when a load is applied. The only way to get it back is to disconnect the input voltage for awhile and then reconnect. For debugging purposes I am using a 50 ohm resister to apply a load to the 5 Volts. Application of the 5 ohm resister does intermittently cause the power supply to stop. I have performed this test on the PMP7389 Eval board and have observed the same results. Is there something I can do to make this circuit less susceptible to loading and unloading??

  • 0
    TI__Expert 5900 points

    Hi,

    Have you found which function of controller was triggered to stop working?

    In PMP7389, there is a TPS2511 for interface. Do you use TPS2511 in your design?

    Regards

  • 0 in reply to Kening Gao
    Prodigy 50 points

    I did have some success with debugging this failure. It appears that the UCC28610 was getting in to a Over voltage latched off state as detected by the ZCD pin. I have added a 10pF cap to the pin and it has not latch off since. I do need to ask if there is a way to recover from an over voltage latch off condition with out disconnecting the AC inputs? This power supply will be hardwired in so it will not be an easy thing to turn off the AC input.

  • 0 in reply to Michael Deck
    TI__Genius 15910 points

    The UCC28610 will always enter into a Latch-off state if an output Over-Voltage is detected, regardless of whether the resistor on MOT is selected within the shutdown/restart range or the latch-off range.  In order to revcover from a latch-off, VDD must cycle through the fault reset level of 6V (typical value).  VDD will not discharge through this threshold until the AC line is removed because the VDD will be regulated by the HVMOSFET during latchoff.

  • 0 in reply to Lisa Dinwoodie
    Prodigy 50 points

    Understood.

    Is the adding of a 10pF capacitor to the ZCD pin a reasonable fix or should I be investigating something else?

  • 0 in reply to Michael Deck
    TI__Genius 15910 points

    adding the 10pF capacitor to ZCD is fine; avoid using anything much larger as the power limit response will be delayed.  This small capacitor should help with line surge testing also so that's a bonus.  Keep in mind that by adding this capacitor, you are also adding a delay to the zero crossing detection circuitry, too much delay and you will miss switching on the valley and result in a small impact to efficiency.  But, if your feeling lucky, adding this small capacitance may actually be fine tuning your circuit to actually switch on the valley in which case you win!  Bottom line, a 10pF cap on ZCD is okay.

  • 0 in reply to Lisa Dinwoodie
    Prodigy 50 points

    Okay. That works. I am still having issues with the devices that I am powering with this power supply circuit. The devices this circuit is powering work fine when being supplied power from a 5Volt wall wart style power supply (or at least I have not got them to fail in this configuration). I have tried adding capacitors, running the supply rail through a Ferrite bead, and a Ferrite in combination with caps. I am still getting a significant ripple at the power input pins of the devices being powered. Do you have any suggestions?