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UCC27201: UCC27201 High Side HO is not Switching, when HI is high . HO Pin remains low when HI pin driven to High

vinay H
Prodigy 15 points
Part Number: UCC27201

Hello,

We are using UCC27201 in one of our application, HO pin of  UCC27201 remains ZERO W.R.T HS always, when HI is driven with high Signal also.

Attached the schematic below

As per device logic table. If HI pin - High & LI pin - Low, I couldn't see the HO pin - High at PWM_OUT1. We getting Zero always at HO W.R.T HS.

Kindly help with above issue we are facing..

Regards,

Vinay 

  • 0
    TI__Prodigy 286 points

    Hi Vinay,

    What are you using to power LI/HI? More specifically, what voltage are you applying to these input pins? Additionally, are you able to receive an output from LO? 

    In order to properly address what is actually happening with your driver, I will need to know more information regarding the schematic. If you can provide more information, I believe I can help you solve your issue.

    Best,

    Avery

  • 0 in reply to Avery Atchley
    TI__Prodigy 286 points

    Hey Vinay,

    Following up on my previous response: the situation you have described sounds like a bootstrap bias issue. In order to solve this issue, you will need to switch on the LI to charge the bootstrap capacitor so that when HI is turned on, there will be a high enough bias between HB and HS that turns on your HO pin. Please reference this article for more information regarding bootstrap circuitry. 

    Hopefully this resolves your issue.

    Best,

    Avery

  • 0 in reply to Avery Atchley
    Prodigy 15 points

    Hi Avery,

    For HI/LI Voltage is coming from Microcontroller which will be 3.3V.

    The below cases signals provided to HI/LI and observed at HO/LO

    Case 1:  HI - 3.3V & LI - 0V & observed the HO side 0V wrt HS and LO - 0V wrt GND.  

    Case 2: HI - 0V & LI - 3.3V & observed the HO side 0V wrt HS and LO - 12V wrt GND.

    In our application we used 2 drivers for H - Bridge

  • 0 in reply to Avery Atchley
    Prodigy 15 points

    If i required HO to turn ON, Is both LI and HI needed to Turn ON?

  • 0 in reply to vinay H
    TI__Prodigy 286 points

    Hi Vinay,

    Turning both HI & LI on at the same time will not turn HO or LO on. This will prevent a shoot-through from occurring, thus protecting the device. Please try the following test and see if it works: 1) Send a pulse to LI to turn LO on then off. 2) With LI now off, send a pulse to HI. Measure the voltage on HO.

    When working with half-bridge drivers, you should aim to turn only one input on at a time. In this case, you need to first turn LI on to charge the bootstrap capacitor. This will allow the bias across HB and HS to rise above the threshold to turn HO on.

    Let me know if this does not work.

    Best,

    Avery

  • 0 in reply to Avery Atchley
    Prodigy 15 points

    Hello ,

    We have tried the both the cases, still its not working.

    First LI is turned ON for 1sec & then OFF, 200msec delay.

    next HI is turned ON, but HO is not turning ON.

    HO is measured wrt HS showing 0V.

    Regards,

    Vinay H M

  • 0 in reply to vinay H
    TI__Prodigy 286 points

    Hi Vinay,

    When powering HO, can you check the voltage drop across HB-HS? Please let me know if this value is close to zero. We can trouble shoot from there.

    Best,

    Avery