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DRV8701: AVDD and DVDD are not Generated after Motor Is connected

Naman Vaidya1
Prodigy 205 points
Part Number: DRV8701

Hi, 

I am using the DRV8701E series and on the assembly, we check that the AVDD and DVDD are generated 4.8V and 3.3V respectively, we then connect a 24V Motor. I am using STM32 to generate the PWM and Direction on the EN and PH pin for DRV but as soon as I connect them the AVDD and DVDD disappear. Even after doing the disconnection, I am not able to get AVDD and DVDD. 

I don't see physical damage on the IC so don't know if it's blown internally. I have a full H bridge system and using NTMFS5C628NLT1G MOSFET.. Also my IDrive is selected for 68K setting to AVDD  Is there any fault that I am triggering which is causing this any advice would be very helpful. 

  • 0
    TI__Guru 55605 points

    Naman,

    Can you please share your schematic?  

    What is the status of the nSLEEP pin?  It should be high and connected externally to a GPIO on your MCU or to an external source <5.5V.  

  • 0 in reply to Ryan Kehr
    Prodigy 205 points

    Hi Ryan,

    Thanks for replying back. I am attaching my schematic. My nSleep pin is powered externally to 4.5V for now but in the schematic, it is going to a RJ45 cable which is connected to a micro which will be pulling it high to 3.3V once the driver starts working properly. 

  • 0 in reply to Naman Vaidya1
    TI__Guru 55605 points

    Naman,

    When the device is in the SLEEP state, AVDD and DVDD will both be zero.  Unless the device is damaged somehow or not getting power from the VM connection, AVDD and DVDD should be as you measured before.  I don't understand how applying PWM/direction commands could cause this to happen.  

    Do you have another board you could check out or try replacing the IC?  You can scope the VM, nSLEEP, and nFAULT pin to see if you are getting a fault condition.  You will need to pull nFAULT up to an external supply like your 4.5V supply to ensure it reads properly since it is currently connected to DVDD.

    Also, I noticed you are paralleling FETs at the output.  We recommend isolating the gates of the paralleled FETs with a 10ohm resistor.  I see 0 ohm in there now. 

  • 0 in reply to Ryan Kehr
    Prodigy 205 points

    Hey Ryan,

    Thanks a lot.

    I try your suggestions, yup I was getting confused the same way why would pwm and direction command damage the ic.

    I am on vacation for a while but will update you on the progress after 22 Nov.

    Naman

  • 0 in reply to Naman Vaidya1
    TI__Guru 55605 points

    Naman,

    OK.  I am going to go ahead and close this for now.  When you return, you can repost.  If the thread is locked due to inactivity, you can click the "Ask a related question" up above and it will start a new post based on this thread.

    I hope you have a nice vacation!