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DRV8301: output waveform issue

Cherry Zhou
Mastermind 22235 points
Part Number: DRV8301

Hi team,

Here's an issue from the customer may need your help:

When output PWM, after connecting to the motor the output side shows the following waveform:

The customer would like to know what's the reason for that. Could you help check this case? Thanks.

Best Regards,

Cherry

  • 0
    TI__Mastermind 26046 points

    Hi Cherry, 

    1. Was this waveform GH_x with respect to GND, or SH_x with respect to GND?
    2. Does the customer report a fault condition? Does nFAULT pin go low or does the FAULT bit get set in SPI?
    3. If so, which fault(s) are reported in the status registers? 

    4. Can the customer share their gate current settings in SPI? Does lowering the gate drive current help or increasing their gate resistor values?

    5. Can the customer share their schematic? 

    Thanks,
    Aaron

  • 0 in reply to Aaron Barrera
    TI__Mastermind 22235 points

    Hi Aaron,

    Thanks for your help.

    Aaron Barrera said:
    Was this waveform GH_x with respect to GND, or SH_x with respect to GND?

    The oscilloscope probe is grounded to GND with respect to the PVDD and the oscilloscope probe input is connected to SH_x.

    Aaron Barrera said:
    Does the customer report a fault condition? Does nFAULT pin go low or does the FAULT bit get set in SPI?

    Due to a design error, the nFAULT pin is not properly indicated, so it is hard  to determine whether there's a fault condition at this time by pin level.

    Aaron Barrera said:
    If so, which fault(s) are reported in the status registers? 

    The SPI status register can check the status normally without turning on the PWM input, but with the PWM on, the acquired state fluctuates significantly and does not properly indicate the fault condition. The customer is looking for the reason as well.

    Aaron Barrera said:
    Can the customer share their gate current settings in SPI? Does lowering the gate drive current help or increasing their gate resistor values?

    Set control register 1 to 0x17C0 (maximum current limit) and control register 2 to 0x180E before starting PWM. The current gate resistance value is 10 ohms, trying to reduce to 1 ohm, but don't help.

    Aaron Barrera said:
    Can the customer share their schematic? 

    And during the measurement, if the B and C phase lower bridge switch tubes are always kept on, does the time input of the A-phase input PWM waveform lower bridge switch tube input signal turn off some of the time, causing some kind of protection? 

    Thanks and regards,

    Cherry

  • 0 in reply to Cherry Zhou
    TI__Mastermind 26506 points

    Hi Cherry,

    Thanks for the response! Would the customer be able to provide a waveform showing the GHx and INHx signal in addition to the SHx signal for the issue that they are seeing? I want to see if the issue is due to the gate not staying on or if there is a different reason. 

    Regards,

    Anthony Lodi

  • 0 in reply to Anthony Lodi
    TI__Mastermind 22235 points

    Hi Anthony Lodi,

    Thanks for your support!

    The GH waveform of the upper bridge arm of the A-phase input PWM is as follows:

    The INH waveform of the upper bridge arm of the phase A input PWM is as follows:

    Phase B leads to the GL waveform of the lower bridge arm is as follows:

    Phase B leads to the INL waveform of the lower bridge arm is as follows:

    Thanks and regards,

    Cherry

  • 0 in reply to Cherry Zhou
    TI__Mastermind 26506 points

    Hi Cherry,

    Thanks for the waveforms! I am seeing some concerning spiking on the input waveforms, and it could be that this is resulting in some brief parasitic turn on of MOSFETs that should be off. Are the inputs being generated by a microcontroller? Are there sources of noise that would be causing these spikes?

    There are limitations in being to analyze the waveforms when the customer is only using 1 probe. It is best to have multiple signals on the same waveform to compare those signals in real time, such as GHA and SHA on the same waveform, and INHA and GHA on the same waveform. If the customer has the ability to use 2 probes, that would help in better analyzing the waveforms to have multiple signals on one oscilloscope capture.

    Regards,

    Anthony Lodi