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UCC256301: About ZCS event

Kaji@PAN
Mastermind 7805 points
Part Number: UCC256301

Hi,

I am considering the circuit using the UUC 25630 device.
With the function of this device, I would like to ask questions about ZCS events.
In the data sheet, when looking at the items related to ZCS Region Prevention, the conditions under which the ZCS signal becomes high are as follows.
At the falling edge of LSON, the polarity of the resonance current is positive
At the falling edge of HSON, the polarity of the resonance current is negative

For example, if the resonance current becomes small and the polarity of the current can not be detected, will the ZCS signal become high?
Also, is there any other condition for the ZCS signal to be high?
Best regards,
  • 0
    TI__Mastermind 27145 points
    Hi Kaji@PAN,

    Thanks for reaching out. Yes, ZCS is detected if ISNS is positive at the LO falling edge or if ISNS is negative at HO falling edge. The polarity detection is the only mechanism to activate a ZCS response from the controller.

    The hysteresis for ISNS polarity detection is 30mV so the ISNS waveform would have to be extremely small in magnitude to cause issues with the polarity detection. If this were to happen either the resonant current is not large enough to drive ZVS switching or the ISNS components are not sized appropriately.

    The device relies on a few internal functions to avoid ZCS switching. It first looks at the adaptive dead time circuit to determine if the switch node is done "slewing" to the other rail. If the slew rate of the switch node is too slow to detect, then the controller will rely on the Ipolarity change to turn on the next FET. In the event that the controller does not detect the "slew done" and the controller fails to detect a change in Ipolarity, the controller will hit its maximum dead time at which point the next FET will be turned on.

    Best Regards,
    Ben Lough