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UCC256303: UCC256303

user3899198
Prodigy 105 points
Part Number: UCC256303

Unfortunatel, after I shut the BW pin and the ISNS pin off, the controller still can not work normally.

DC-DC Converter-1.pdf

  • 0
    TI__Mastermind 32220 points
    Hello Li,

    Thank you for your interest in the UCC25603 LLC controller.

    From the screen capture, we see a 1-s repetition of RVCC. Table 2 in the UCC256303 datasheet (page 35) indicates that there is a FAULT condition, which waits 1 second between re-start attempts. You need to determine which fault condition exists that is preventing start-up. Check the state of each input pin to the datasheet to make sure that all pins are at their proper level for start-up and running.

    For example, you state that BW and ISNS are "shut off". Does this mean that you grounded these inputs, or opened them?
    The controller needs to see an AC signal at ISNS input to continue running. BW can be grounded and the controller will run, but output OVP will be disabled.

    Check other inputs like BLK and LL/SS for proper input levels. You will need to zoom in on signals like LO and HO to observe how they behave after RVCC rises, to help determine what kind of fault is occurring. Check the operation of the half-bridge MOSFETs to see if they follow the LO and HO signals. Observe each input and output to see which one is not behaving as expected, then fix the problem that is causing the unexpected behavior.

    Regards,
    Ulrich
  • 0 in reply to Ulrich Goerke
    Prodigy 105 points
    Hi Ulrich,

    My BLK is 3.3V, adequate to get the controller start working, but LL/SS pin is always zero, and the Lo &Ho are always low level. My VCR pin is always at 3V level without any fluctuation.

    I tried imposing a external 100kHz , 2V Pk-Pk sinusoidal wave at the ISNS pin, but nothing seemed changed, the controller still can not work properly.

    Thanks for your kind explnantion.
  • 0 in reply to user3899198
    TI__Mastermind 32220 points
    Hi Li,

    I think the LL/SS pin should not be always zero. It should rise for soft-start.
    Please check the pin and the components attached to it for a possible short to GND.

    Regards,
    Ulrich
  • 0 in reply to Ulrich Goerke
    TI__Mastermind 32220 points

    Hello Li,

    It has been some time since my last posting, with no further reply.

    Given that, I will close this thread.  If you have any further issues, please start with a new post.

    Regards,
    Ulrich