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UCC27211: UCC27211ADRMT HO does not go low when HI is low.

Vikram Laisetti
Prodigy 40 points
Part Number: UCC27211

Hi,

I have already created the ticket for this case in TI, the case number is CS1647971. But the support team recommended me to submit a ticket in E2E. So, here is my question 


 I am from a medical device company in Massachusetts. We are using about 1000 of these parts in our system, recently I found out that the chip HO does not go low when HI is low. I have a question about part UCC27211ADRMT, We have been using this part for a long time, I am trying to cutoff the phase lines of the motor by cutting off the gate driver inputs when over current trigger. But when the overcurrent triggers, and I turn off the LI, HI but the Ho goes low very slowly. 

 

  • 0 in reply to Vikram Laisetti
    TI__Intellectual 2100 points

    Hi Vikram,

    Thank you for reaching out and sharing the schematic! It looks like you have all the necessary components in place.

    Are you able to share screen captures of your waveforms? Specifically, can you capture the inputs LI, HI and outputs LO, and HO? I am hoping this will give the team a better indication of what is going on here.

    Best,

    Alex W

  • 0 in reply to Alex Weaver
    Prodigy 40 points


    Here: Yellow is HI, Deep-Blue is LI, Purple is HO, Cyan is LO.

    When we set both HI and LI to low the HO goes low very slow as you can see in the picture.

  • 0 in reply to Vikram Laisetti
    TI__Intellectual 2100 points

    Hi Vikram,

    Your HO output actually needs to be measured as a differential voltage with respect to the switch node (HO-HS). Or, you could subtract the switch node waveform from your HO waveform and get the same result. This also helps explain why your HO waveform reaches a peak of Vpp = 45.2V, while LO reaches a peak of Vpp = 13.8V.

    The drop in HO when HI goes low shows the device is functioning properly. The remaining voltage on HO can be attributed to the switch node. Once you take the HO measurement as a differential voltage referenced to the switch node (HS) rather than being referenced to ground, I believe you will see the device working as expected.

    Best,

    Alex Weaver