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Original question:

DRV8307: Motor not starting up at -15C

DRV8307: Motor not starting up at -15C + Extra Info

Robert Gilmore
Prodigy 30 points
Part Number: DRV8307
Other Parts Discussed in Thread: DRV8308,

Tool/software:

I have a design that functions well at temperatures -10C or higher. However, I have test that consistently fails on multiple samples at -15C. 

The motor simply does not start up, and the motor driver faults out. I can raise the temperature, power cycle, and the motor driver will operate again.

Can TI evaluate the schematic attached, for any risks at low temperature. Is this an issue that you have seen before?

I have monitored the FAULTN signal and it never goes low to indicate a fault. One interesting point is that this fault occurs when I power the device from a switch (i.e. a harsh switch on), while when powered on from a bench power supply and the voltage rises more gently, the fault does not occur. 

On the same device, I have a 2nd TI motor driver - this time DRV8308. It never faults out in this way at cold temperatures. 

  • 0
    TI__Genius 15225 points

    Hi Robert,

    Not sure what could be happening here but it'd be interesting to see some waveforms of VM, VCP and nFAULT at start up?

    Regards,

    Yara

  • 0 in reply to Yara Al Shami
    Prodigy 30 points

    Hi, here is nFAULT at start up, at -20C.With a connection by switch.



    Here is is when I press the bench PSU button and the voltage ramps slower. 

    I will try to get you VCP and VM. 

  • 0 in reply to Robert Gilmore
    TI__Genius 15225 points

    Hi Robert,

    looks like the peak value of nFAULT in the first waveform is somewhere around 6V-8V correct? You could be damaging your fault pin:

    Feel free to post VCP and VM as soon as you capture them.

    Regards,

    Yara

  • 0 in reply to Yara Al Shami
    Prodigy 30 points

    Hi Yara, 

    Here are some start-up plots at room temperature (approx. 20C), while starting up with a switch. 





    Here they are at -20C




    I observe a faster rise time, but similar peak. What do you make of these plots? Any Insights?

    Thanks, 

    Rob

  • 0 in reply to Robert Gilmore
    TI__Genius 15225 points

    Hi Rob,

    Looking at your previous waveform of nFAULT can you confirm whether I've labeled it right? nFAULT reaches 8V? and it looks like there are some transients that I've circled in red.

    even on your new plots nFAULT is already at 2V before the VM starts ramping up. Are you measuring nFAULT with respect to GND?

    That would tell us whether you're really violating an abs max or not.

    Regards,

    Yara

  • 0 in reply to Yara Al Shami
    Prodigy 30 points

    Hi Yara, 

    I am confident that the spikes you have circled are only noise picked up on long wires that are exiting a thermal chamber to allow for oscilloscope probing. Since this, I have improved the coupling with GND by running a GND wire adjacent to the signals of interest, which has cleaned up the plot.

    Here's some more plots. The first one is when I connect a switch to the positive supply to the device at -20C.




    This is when I connect a switch to the negative supply at -20C.

    In both cases, the motor would not start, but when started from the power supply button, it worked normally.


    I'm not certain why the signals appear to have 2V offset, I assumed this was floating. I will look into this as it may have something to do with my test setup. 

    If there any other plots, or information I can provide to you - please let me know. 

    Thank you, 

    Rob

  • 0 in reply to Robert Gilmore
    TI__Genius 15225 points

    Hi Rob,

    I'd be interested in seeing waveforms of the gate pins during start up.

    also I noticed this E2E thread is referenced in your original question:

    https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1441571/drv8307-motor-not-starting-up-at--15c

    Did you change your gate resistors?

    Regards,

    Yara

  • 0 in reply to Yara Al Shami
    Prodigy 30 points

    Hi, 

    On this PCBA, we have a DRV8308 and a DRV8307

    The DRV8308 drives the same MOSFETs (Vishay SI7938DP-T1-GE3) as the DRV8307 which works normally at cold temperatures. 

    The DRV8308 has 0 ohm gate drive resistors, while the DRV8307 has 68 Ohm gate drive resistors.

    The load seen on the DRV8308 FETs is higher (max 10A) to the the DRV8307 FETs (max 1A).

    I'll try to get some scope plots. This is challenging due to needing to run long lengths of wire out of the cold chamber we are using.

    Rob

  • 0 in reply to Robert Gilmore
    TI__Genius 15225 points

    Hi Robert,

    Any update on gate output waveforms? Could capture UHSG-U, U-GND, ULSG-GND?

    Regards,

    Yara