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drv8811 stop

sng conrad
Prodigy 30 points
Other Parts Discussed in Thread: DRV8811

Hi sir,I have this problem with some of my drv8811 ics. seems at sometime, the ics can function ans drive the steppers but someitmes, it hust stops functioning despite the right signals being sent from my mcu. i have to resolder the legs of the drv8811 and maybe the supporting components and sometimes afetr doing this, the ic starts to succesfuly control the stepper motor again. can anyone shed some ligjt on this?

i am pretty sure the schematic and circuit is corect elae i wont expect the steppers to orj at all. i dont think this is a thermal shuntdown isue as wel as the steppers just stops functionng even before running,.. 

thanks for any advise on this...

my email raddy@singnet.com.sg

conrad

  • TI__Expert 7455 points

    Hi Conrad,

    This could be an over current problem. What is the application voltage and what current are you trying to drive?

    It is also very important for the PowerPAD to be soldered properly into the board.

    One last item which must be taken under consideration is that although the schematic may be 100% correct, the layout still plays a role, so it would be wise to make sure there are no areas which can induce sensibilities into the design.

    Best regards,

    Jose Quinones

  • in reply to Jose Quinones
    Prodigy 30 points

    hi jose,

    thanks for your advise,

    i think the rc may be the issue. the capacitor i am using at the moment is 220p and 220k which is too small and too huge. i will try to change the cap to at least 1nf and 10k tomorow and see if that is the issue.

  • in reply to sng conrad
    TI__Expert 7455 points

    Hi Conrad,

    Those values are definitely off the range. I would try to limit the Rx to no less than 12K ohms. The cap at 1000 pf is a good choice.

    I hope this solves your problems.

    Best regards,

    Jose Quinones

  • in reply to Jose Quinones
    Prodigy 30 points

    HI Jose,

    thanks for the advise. I just tested with a change in the R&C values this morning, and the steppers are working very fine now..

    Now i am solving a +5v supply noise issue i believe as sometimes, a reset is done to my ain MCU halfway during the running process.

    I believe a simple cap along the +5v and GND line will solve this.

    The steppers are also on the noisy side, but i think such a cap will also soften the motors.

    Thks

    Sincerely,

    Conrad

  • in reply to sng conrad
    TI__Expert 7455 points

    Hi Conrad,

    Glad to hear it is working better now. For motor noise, you will want to play with the DECAY pin. Fast decay is usually noisy due to ripple current, but if you get a good ratio, noise is reduced considerably.

    Here is a video I recorded some time ago showing the effects of the DECAY pin on the winding current. http://www.youtube.com/watch?v=Wf8rN3bV8XM&list=UUNTi4Drb3WqJ68Zdcudo4zg&index=6&feature=plcp. Feel free to fast forward to time 3:50 where I show how the current looks and what DECAY does to it.

    Best regards,

    Jose Quinones