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DRV8701: No Output

Prateek Verma70
Prodigy 50 points
Part Number: DRV8701

Hello Everyone,

I am developing a Motor Driver Circuit using DRV8701P for one of my projects.

Unfortunately, I am not getting any output pulse on Gate pins. I am sharing my schematic for the same. 

In the schematic, IDRIVE resistor is not fitted. Also, I have tried different combinations to make it work such as removing R2 and shorting R3 & R_SENSE. Still no Output.

  • 0
    TI__Guru** 114905 points
    Hi Prateek,

    When you expect the pulses on the GLx and GHx pins, what are the voltages around the DRV8701?
    nSLEEP
    nFAULT
    AVDD
    DVDD
    VCP
    VM

    nSLEEP is connected to the Sense Block. Is it driven to a logic high to enable the DRV8701?
  • 0 in reply to Rick Duncan
    Prodigy 50 points

     Hi Duncan,

    The connections I have given are:

    INPUT:-

    nSLEEP = 5V .. Yes, it is driven high to enable the DRV8701.

    VM = 12V

    IN1 = 5V & IN2 = 0V [GND]

    OUTPUT:-

    nFAULT = 0V

    AVDD = 4.95 V

    DVDD = 3.27 V

    VCP = 21.9 V

    V in GLx = 0.03V and V in GHx = 0.01V

    For Vref, I have tried different combinations 1. Potential divider setup in which I am getting 3.25V for R2 = 2K and R3 = 3.3K 2. Shorting Vref to AVDD, Vref = AVDD.

    After trying out many different configurations, as mentioned in the datasheet, I still haven't come up with any solution. I have really confused since this being a comparatively simple circuit I don't understand what I am messing up.

    Thank you for your acknowledgment. Do let me know if you have any suggestions. :)

     

  • 0 in reply to Prateek Verma70
    TI__Guru** 114905 points
    Hi Prateek,

    Thank you for the information.

    Since nFAULT pin = 0, a fault is being reported. The two most likely faults are OCP and PDF (see Table 7 of the datasheet).

    Please check the nFAULT pin with a scope to determine if the nFAULT pin is releasing every 3ms for a few us. This is confirmation that the fault is OCP or PDF.

    Next please check the GLx and GHx outputs to determine if they are driven properly.

    Also, please note pins 14 and 15 of the DRV8701 are incorrectly labeled in your schematic. Pin 14 is IN2 and Pin 15 is IN1.

    If you need additional assistance, please provide scope captures of the nFAULT rising as the trigger and the following signals pairs:

    GL1, GH1, and SH1
    GL2, GH2, and SH2
  • 0 in reply to Rick Duncan
    Prodigy 50 points

    Hi Duncan,

    I have probed the nFAULT pin. After pressing the Autoset button on scope I am getting these outputs. I am not sure what do these comply. Please have a look at it and tell me your view.

    Also, I have thoroughly reviewed the OCP and PDF Faults and believe its not PDF because none of the gate pins are shorted to VM, GND or SHx. Most importantly, I have not yet connected the FETs just measuring the output on Gate pins so I doubt it could be OCP.

    Thank you.

  • 0 in reply to Prateek Verma70
    TI__Guru** 114905 points
    Hi Prateek,

    Thank you for the additional information and the scope capture.

    The scope capture shows nFAULT going low for approximately 3.2ms. This is consistent with an OCP event.

    Also the OCP is monitoring the voltage from VM to SHx. Without the high side FETs, the VDS voltage can be much higher than 1V. This is probably the reason for the OCP faults.

    Please connect the FETs and retry.