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DRV8353R: -350mV undershoot at pin 27 (SDO for SPI Communication)

Ben G
Prodigy 110 points
Part Number: DRV8353R

I'm currently getting around a -0.35V undershoot at my SDO pin and was hoping to figure out what is causing it and if it's a problem. I have a termination resistor that eliminates the undershoot at the side of my controller, but is the undershoot harmful to the motor driver?

Additional information:

Fall time = ~1ns

Pull-up resistor = 1k to 3.3V

  • 0
    TI__Mastermind 21805 points

    Hello Ben,

    That may indicate some ground bouncing. The pin itself is self-protected by the open drain MOSFET body diode so I do not have a concern about the voltage level. Does the undershoot only occur when the SDO pin is switching or does it correspond to cases when the motor is running? Is the SDO ground common between the DRV8353R and the MCU? If not, where are they connected?

    Thanks,

    Matt

  • 0 in reply to Matt Hein
    Prodigy 110 points

    Hi Matt,

    Thank you for the prompt reply. To answer your questions, the undershoot only occurs when the SDO pin is switching. I have not tested the signal with a motor connected thus far. The DRV8353R and the MCU are referenced to the same ground plane. 

    -Ben

  • 0 in reply to Ben G
    TI__Mastermind 21805 points

    Hi Ben,

    Any significant capacitance, either due to components or long traces between the MCU and DRV? It could just be due to the parasitic inductance and capacitance of the trace.

    I don't have any concerns about this voltage causing any issues to the DRV.

    Thanks,

    Matt

  • 0 in reply to Matt Hein
    Prodigy 110 points

    I don't see much capacitance between the MCU and DRV. The trace length is 1721mil with a delay of 293ps. No external capacitance was added to signal path and my MCU's pin capacitance is ~5pF. 

  • 0 in reply to Ben G
    TI__Mastermind 21805 points

    Ok, either way I am not concerned with you damaging the driver.

    Thanks,

    Matt