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Original question:

UCC27211: LO = H is output even though LI = L is input when VDD starts up.

UCC27211: Missing pulse issue of the high side driver

Jason Shen
Intellectual 1945 points
Part Number: UCC27211

Dears

We have an application of DCDC with 15V input and 5V output, in this case, the UCC27211 have 12V supply to drive the MOSFET. We have found the high side output not follow the high side input, when the DCDC load current increase.

So we are wondering if there have some internal protection except the UVLO? If the voltage on the Cboot is very stable of 11.7V, is there any possible that this device output not follow the input of the high side driver? the low side works well.

Thanks

Jun Shen

  • 0
    TI__Expert 4480 points

    Hi Jun, 

    Our expert on this device is out of office at this moment, please expect a reply in the next business day. 

    Thanks so much,

    Vivian

  • 0 in reply to Vivian Qi
    TI__Genius 9301 points

    Hi Jun, 

    Thank you for contacting us. Are you able to share scope shots of the behavior? These plots would help understand the issue (please capture using tip and barrel method for signals referenced to VSS and differential probes for signals referenced to HS):

    * HI-VSS, LI-VSS, HO-HS, LO-VSS

    * VDD-VSS, HS-VSS, HO-HS, HB-HS

    What is the switching frequency, VDD supply level to power the driver and the MOSFET PN?

    Lastly, if you can share the schematic I can review it to make sure it follows our recommendations.

    Regards,

    Leslie

  • 0 in reply to Leslie Marquez
    TI__Genius 9301 points

    Hi Jun, 

    I'm closing this thread to avoid confusion, since we are already handling this issue directly by email. 

    Best regards,

    Leslie