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DRV8701: DRV8701P Affect output current capability factors

user4370495
Expert 1155 points
Part Number: DRV8701

Dear :

Setting: the frequency=20K,  Rsense=0.01Ω  Vref=2V
So Ichop=2v/20k*0.01=10A.  Rdriver=100K  connect to AVDD.

 I found  when Duty=50%,  I block the motor, and the output current reach 5~6A ,The motor will easily stop .
change the duty to 100%,  I block the motor , the motor will not be easily stop.
Actually, I hope the output current can reach 10A, even the duty reach to 50%, so i think, there maybe something wrong on the sch.
Pls help to confirm this ,thanks

  • 0
    Expert 1155 points

    Part Number: DRV8701

    Dear TI:

    Waveform and SCH.8701P Issues.docx
    Ver .A  the circuit works normal.
    Ver B. Change  MCU(p2p but more flash.)  But the circuit can't work. the motor stop work.
    Note: the sch and pcb layout are all the same. 
    from the waveform, it seems the decay time become longer.
    how can i do to optimize the waveform ,and make the motor move smoothly. thanks

     

  • 0
    TI__Guru 56650 points
    Hello,

    The attached file's SH1 waveform can give us a clue. Good board: the SH1high plateau is flat. Bad board: the SH1 shows a LC resonant waveform after SH1 high. LC resonant means GH1 turns off the high side FET. Does the output current hit the current chopping Drain threshold?
    Could you check SNSOUT and VREF voltage and waveform between the good board and bad board?
  • 0
    TI__Expert 8985 points
    Hi user,

    Is there 100% assurance only the MCU was changed in the hardware?

    No other changes were done to the software?

    There are four columns on the document. Can you specify the differences between each four?

    Is there a fault generated when the motor stops?

    Is it just a motor stall?

    Magnitudes appear different between scopes on columns 1 and 3 of SH2 and GH2. Is this magnitude difference intentional?
  • 0 in reply to Wang5577
    Expert 1155 points

    Dear  Wang:

    thanks for advise. i have double check.
    Ichop= (2-0.05)/20*0,01= 9.75A  (Vref=2.0v). so it can not hit the current chop. snsout in high level.

    the motor can move now, but the current only 3A ,  But the good board can reach 6-7A. 
    Vso=200mv nomal , when block  the Vso=600mv .

    i want to enlarge the current, how the check the circuit,  thanks 
    By the way, the power source can output 10A current.

  • 0 in reply to user4370495
    Expert 1155 points

    Dear  Wang:

    i check  SP and  SNSOUT  Pin ,And found it's OCP protect.
    when i block the motor, i found SP Voltage >1V , so it's trigger OCP Protect.
    SP Waveform:

    SNSOUT Waveform:



    so now i want to change RIDRIVE  Valve. can you give me some advise ?

  • 0 in reply to user4370495
    TI__Guru 56650 points
    Hello,

    OCP has 4.5us deglitch time. If the scope shows 1us/div, I am not sure it is OCP event. Also, waveforms in "8701P Issues.docx" don't match your latest waveform. Would you use 2 or more probes to show few checking point together?
  • 0 in reply to Wang5577
    TI__Guru 56650 points
    Let me close this thread since we don't have any update from 4/2. You can reopen it by posting your update.
  • 0 in reply to Wang5577
    Expert 1155 points

    Dear wang:

    thanks a lot. the problem is resolved. 
    i change the Vref value to 4.8v(connect to AVDD), and change the Rsense value to 5mΩ。 so it work normally.
    I was a little confused  does output current limit and chopping current the same mean?
    thanks.