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UCC27200: HO remains HIGH even after giving PWM input to HI

Ishan Panchal
Intellectual 640 points
Part Number: UCC27200
Other Parts Discussed in Thread: UCC27201

Hi There,

We are trying to get output PWM's at the HO pin of UCC27200. We have followed the application implementation guide but still we are not getting any output.

We also tried soldering chip on a breakout but no luck. 

Please see attached schematic snap for your kind reference.

Note : Replaced R110 10R with 0R. 

Is there any default setup which the driver needs, to enable the outputs ?

Thanks..!!!

  • 0
    TI__Genius 13216 points

    Hi Alex,

    Thank you for posting your question on E2E. 

    What is HS connected to in your circuit? One cause of this issue may be HS not switching to ground. If HS is not switching to ground, it may not allow the bootstrap capacitor to charge enough in order to overcome the HS/HB UVLO threshold.

    Here is an excerpt about this threshold from the datasheet: "The VHB UVLO disables only the high-side driver when the VHB to VHS differential voltage is below the specified threshold. The VHB UVLO rising threshold is 6.7 V with 0.4-V hysteresis"

    One way to check this would be to measure HB-HS using a tip and barrel probe.

    Thanks,

    Daniel W

  • 0 in reply to Daniel W
    Intellectual 640 points

    Hi Daniel,

    The HS pin is connected to SOURCE of high side FETs. Please see attached PDF of FET section in our circuit for your kind reference. 

    I did checked the HS pins wrt to HB and it remains at VCC level of 12V.

    One thing to consider, we are giving 3.3V logic inputs to HI and LI, but as per datasheet it says CMOS threshold is 5.8V for VCC of 12V. Can this be the issue ? I tried giving 12VCC on HI but the HO didn't go high. At this time, the FETs were connected and FETs supply VDC was given 12V.

    Can we order UCC27201 for 3.3V logic level inputs ? 

    Thanks..!!!

  • 0 in reply to Ishan Panchal
    TI__Genius 13216 points

    Hi Alex,

    Thank you for the additional information. You are correct that 3.3V is too low for the UCC27200 threshold of 5.4/5.8V. However, the UCC27201 has a threshold of 1.6/1.7V and should work with a 3.3V logical input.

    Thanks,

    Daniel W

  • 0 in reply to Daniel W
    Intellectual 640 points

    Hi Daniel,

    Thanks for the confirmation on logic levels..!!!

    As of now, I don't have UCC27201 so I am planning to provide 5V logic inputs to UCC27200 using arduino. As per datasheet for a VCC of 9VDC to the UCC27200 a threshold level of 4.32V minimum would be required. I think this should work without any issue, right ?

    Thanks..!!!

  • 0 in reply to Ishan Panchal
    TI__Genius 13216 points

    Hi Alex,

    I do not see the 9V VDD/4.32V input specified in the datasheet. Could you specify where these numbers are from?

    Thanks,

    Daniel W

  • 0 in reply to Daniel W
    Intellectual 640 points

    Hi Daniel,

    I was referring the graph in Fig.6 where it shows that input rising threshold is nearly 48% for VDD around 8-9VDC. Based on this I calculated the 4.32V level for 9VDC input. But in section 6.5, I noticed that typical rising threshold voltage level is 5.8VDC. Therefore I provided inputs at 6VDC and the driver works fine.

    I do feel that CMOS and TTL logic level chip datasheets should be separate to avoid any confusion.

    Appreciate your kind support and concern. Thank you so much..!!!

  • 0 in reply to Ishan Panchal
    TI__Genius 13216 points

    Hi Alex,

    Thank you for the clarification. I am glad you were able to resolve this issue.

    Thanks,

    Daniel W

  • 0 in reply to Daniel W
    Intellectual 640 points

    Hi Daniel,

    We have the TTL version UCC27201 in house now. We are giving the PWM inputs to Hi pin at 60% duty cycle but still we are facing issues with the High side  output of driver. The HO remains low wrt HS, we have given PWM inputs at 60% duty cycle. The low side driver works perfectly. One thing that I observed is that voltage across bootstrap capacitor remains around 2VDC. The voltage on HB pin is around 12V wrt GND and on HS pin it is around 8VDC wrt GND. Please let me know your thoughts on same.

    Attached is the schemativ of FETs where the gate driver connects, I have already shared Gate Driver section previously.
    Thanks..!!!BLDC FET Connections.pdf

  • 0 in reply to Ishan Panchal
    Intellectual 361 points

    Hi,,,,,
    we have Same issue as above you mention please answer as as soon as possible we are in critical mode of project,
    and Alex if you solve this big issue please revert back as soon as possible.
    please help us!!!!!!!!   

  • 0 in reply to Ishan Panchal
    TI__Genius 13216 points

    Hi Alex,

    The UCC27201 has undervoltage protection for the high side driver which will not allow the driver to turn on if the voltage across the bootstrap capacitor is less than about 6.7V. 

    Please take a scope shot of HS wrt GND and HB wrt HS.

    Thanks,

    Daniel W