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UCC27201A-Q1: Bootstrap Soft Charge Problem

Firat Dede
Prodigy 10 points
Part Number: UCC27201A-Q1

Hi,

I designed one mosfet motor driver with this UCC27201A-Q1 IC. And at inputs I am using Pic16F1824 5V PIC. 

I am trying to use 15 Khz PWM to High Input and logic input lo Low input (0V or 5V). But High side mosfet is not fully turn on due to bootstrap charge problem.

I changed frequency from 1kz to 28khz with several values no change.

Also changed bootstrap capacitor with 100nF to 1uF values no change. I have oscilloscope, When I probe bootstrap capacitor I am seeing saw style voltage signals like some leak of soft charge.

My pwm cycle is usually %80-85-90.

But bootstrap is not charging. What I am doing wrong?. Here my circuit. I only draw half bridge, other half is same. 
Should I give PWM to low input too?

  • 0
    TI__Expert 7395 points
    Firat,
    Thanks for your interest in TI here. I've contacted the relevant product group. You should hear from them soon.
    Regards
    John
  • 0
    TI__Intellectual 2910 points
    Firat,

    I am sorry to hear that you are experiencing undesired behavior in your design. I do not see an issue with your circuit schematic. I understand tat you have tried a few different changes and the behavior remains. Could you please share an oscilloscope screen capture, showing HI, LI, HB, and HS? Also one with HI, LI, HO, and LO, would be informational. What is the HI/LI dead time?

    Please try running without the TVS diode. There is a possiblity that the high-side diode is starting to conduct and causing an undesired current draw on the HB supply. If this resolves the issue, we can look at a different approach to protect the gates.

    We could also take look at the layout. The bootstrap cap should be located as close as possible to the driver HB and HS pins. Also, at least one of your VDD bypass caps should be as close as possible to the VDD and VSS pins on the UCC27201A-Q1 device.

    Looking forward to your update.

    - Daniel