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UCC256402: How is OCP validated and tested

Tony xiong
Intellectual 670 points
Part Number: UCC256402

Hi  Friends:

             I want to verify OCP's functionality. Is there any way to verify OCP's functionality?

OCP1 / OCP2 / OCP3, what are the methods of verification respectively;

Thank you

  • 0
    TI__Guru* 85926 points

    Hello,

    Sure there is adjust the output current and monitor the ISNS, DRV, HO and lower pins and vary the load on the output just make sure the device does what is supposed to based on the block diagram, the capacitor dividers and the VISNSE_OCP1/2/3 thresholds specified in the data sheet.

    I would also recommend that your resonant capacitor, VCR and ISNS dividers are setup correctly for this as well.  You can use the equations in the data sheet or the excel design tool that can be found at the following link.  http://www.ti.com/lit/zip/sluc675

    Regards,

  • 0 in reply to Mike O'
    Intellectual 670 points

    Hi  Mike;

            Thank you for your reply in time;

    Then  I have some other question;

    1、 yellow show Vcc waveform;Blue show Rvcc waveform; Vcc  capacitor voltage is fast  discharging;What caused the problem; how to resolve the problem

    2、Is there a reference design for PFC+UCC256402；

    Thank you

  • 0 in reply to Tony xiong
    TI__Guru* 85926 points

    Hello,

    When the UCC256402 sees a fault such as over current or over voltage it will stop switching  and VCC will cycle between VCCstartself (26V) and VCCRestartJfet(9.65V).

    Your design when it comes up is hitting a fault.  RVCC does not seem to have time to charge up during the faults.

    Consider rechecking your designs VCR, ISNS and BLK dividers with the excel tool to make sure they were selected correctly.  If the BLK divider was setup incorrectly and the LLC is starting up at too low of a voltage it could also contribute to excessive current during startup. 

    You can also double check these signals with an oscilloscope along with the VDD and RVCC pins as well.  To try to figure out why your design is shutting down. 

    Regards,