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UCC27712: UCC27712 toff HI LO off time too long

Ue
Genius 17165 points
Part Number: UCC27712

Hi all

Please find a customer question regarding the toff for the UCC27712 copied below.

Please review and comment.

Best regards

Ueli

--------------------------------

We are using the UCC27712 where the Datasheet states HI LO Off Time of typ. 45ns

Looking at our application with a HI-LO-HI time of 190ns the driver doesn’t switch off:

channel 3 PWM input: delta x = 190ns low time

channel 1 HI OUT: remains high

It requires a low-time of 370ns at the PWM input for the high-side output to switch

For a 50kHz PWM at the input we are seeing a 1kHz high side output

 (we suspect because of  the  High Side UVLO).

 

  • +1
    TI__Mastermind 23015 points

    Hello Ueli,

    Thank you for supporting the UCC27712. Based on the waveforms there is a longer delay than expected but we need to confirm some details of the application circuit. Is the waveform shown for the driver input confirmed to be the signals at the driver IC input pin, Hi and COM? Can you confirm if there is an R/C filter or network on the driver inputs, and the signal shown on the plots may be the signal going into the R/C filter network.

    It also seems that the delay is longer than expected of the input falling edge to the driver output starting to fall, which makes me think there is likely some tilter delay not shown in the scope plots.

    For the second comment: for a 50kHz input we are seeing a 1kHz high side output. Can you provide more information and scope plots of this behavior? Can you show the driver input at the driver IC input pins, driver output (HO-HS with differential probe if available), and HS signals. Show at wide time base showing when the HO responds relative to the HI input. And also zoomed in time scale of when the HO responds and also on the cycles where HO is not responding.

    Regards,

  • +1 in reply to Richard Herring
    TI__Mastermind 23015 points

    Hello Ueli,

    It has been a while since our last communication. We assume you may have resolved the issue on the thread. If there are any additional questions you can  post on this thread.

    Regards,

  • +1
    TI__Genius 17165 points

    Hello Richard

    That is correct, you answered all customer questions by email.

    I appreciate your support, thank you !

    Ueli