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DRV120: Current drop to zero after peak and then attempts to recover back to the HOLD level.

Chad Southwell
Prodigy 90 points
Part Number: DRV120
Other Parts Discussed in Thread: DRV110

Rpeak = 100k

Rhold = 100k

Rosc = 200k

Ckeep = 1uf

Vin = 24Vdc

Cbypass = 4.7uf/50v

Fluid Valve = Parker 002-0010-900

Current probe TCP0020

Current drops to zero at random intervals. Any tips?

  • 0
    TI__Expert 4940 points
    Hi Chad,



    I have contacted our expert regarding this issue, you'll question will be answer soon.



    Regards,

    Costin
  • 0
    TI__Intellectual 1965 points

    Hi Chad,

    I see the issue you are having. Is your setup the same as before, where there were no issues at F_PWM=5kHz and 10kHz?

    I'm curious about the low-frequency oscillations in the current, particularly at the peak current. Can you post a close-up of the peak current waveform and the OUT voltage, showing one cycle of the low-frequency oscillation?

    Additionally, can you post the relevant schematics of your circuit?

    Best,

    Grant

  • 0 in reply to Grant Falkenburg
    Prodigy 90 points

    Hi Grant.

    I went back to the 20kHz osc. just so we can see the initial problem. I'm thinking the inductance is messing with the PWM behavior during the HOLD state. That being said, and upon reading the description on how device works during HOLD, I fail to understand why the HOLD state is failing. I'm juggling several design flows at this time. If you have some suggestions please let me know and I tweak the design.

    The wire connection to the fluid valve 22awg, stranded wire, 4 inches long.

    Thanks,

    Chad

  • 0 in reply to Chad Southwell
    TI__Intellectual 1965 points

    Hi Chad,

    May I suggest one change to your schematic: use a fast recovery diode for D1. It could be that the diode's slow turn-on time is causing voltage spikes on the OUT pin, which is only rated for 28V. The STTH2R06 diode used on the DRV110 EVM has the same SMA package as the MRA4004 you are using.

    I would still like to see a close-up of the low frequency current oscillations. Having low frequency oscillations is not uncommon for the DRV110, but typically the peak current of each oscillation (not to be confused with the peak current setting) should be constant.

    Best,
    Grant

  • 0 in reply to Grant Falkenburg
    Prodigy 90 points

    Grant,

    Thanks for the diode suggestion, I'll give it a shot this week and let you know.

    Chad

  • 0 in reply to Chad Southwell
    TI__Intellectual 1965 points

    Hi Chad,

    Sounds good. Should that not solve your issue, please provide the scope captures of the low frequency current oscillations and the OUT pin voltage.

    Best,

    Grant

  • 0 in reply to Grant Falkenburg
    Prodigy 90 points

    Grant,

    The fast diode did the trick, I had a MURS160T3 laying about.

    Using the same resistor values (20kHz osc), only change was the diode.

    The circuit does sing at about 10kHz during the PWM hold state of the design.

    Chad

  • 0 in reply to Chad Southwell
    TI__Intellectual 1965 points

    Hi Chad,

    Excellent! I'm glad that switching the diode solved your issue.

    Regarding the 10kHz ringing, you can try changing the PWM frequency between 15kHz and 25kHz to find a more stable value.

    Please let me know if you have any more questions.

    Best,
    Grant