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UCC24612: issue detecting and blanking

claudio tasso
Prodigy 20 points
Part Number: UCC24612

Hi Sir 

Prefact: we are developing LLC resonant converter , 24Vdc and 40A , 

Rectifier FET are FDBL86361-F085

We are facing a problem using the device as specified (-2) , as you see on scope screen , negative treshold is detected , but we expect to see a full conduction till the current rise a lower value, can you pleasse clarify this issue , the circuit is exactly what you suggested in AP note.

We also noted that Vgate is around 6V and not 9.5 as specified.

Vreg is 9.5.

Hope you can help with described issue.

Have a grat day.

  • 0
    TI__Mastermind 27135 points
    Hi Claudio,

    Thanks for your interest in UCC24612. Could you share waveforms of the voltage between VD and VS pins? Do you see this issue in both legs on the secondary or only one? Also do you see this issue under all operating conditions or only certain points?

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 20 points

    Hi Benjamin

    We have same issue on both devices (same), when we have lower current (5A) they work only 1/4 conduction , and it seems worst then 40A situation, when we increase current they work as you seen in previuos waveform attached. I expext a blanking of 540nS but we have no full clear what is happening .

  • 0 in reply to claudio tasso
    TI__Mastermind 27135 points
    Hi Claudio,

    Could you try using a MOSFET with larger Rdson? The controller is looking at the drain to source voltage of the FET. The low Rdson of the FET might be causing problems sensing the voltage drop across the FET and is terminating the gate voltage early as a result.

    Best Regards,
    Ben Lough