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drv8811 problem

hardik padhariya
Prodigy 150 points
Other Parts Discussed in Thread: DRV8811

hello frndz.....

i m working on arduino board...

i have made it prototype

when i connect a motor and give an input motor does not rotate...and when i increase the current it starts rotating without any input...

what i measure is that when motor not connected..

voltage on pin 6 and 9  is 3.03 but when i connect the motor voltage on pin 6 becomes 2.46v and on pin9-1.91v...

and i also measure on original arduino board ,after connecting the motor voltage on pin6 and 9 remains same...

i also put an match pair resistors on these two pins but the situation is same...

  • TI__Expert 7455 points

    Hi Hardik,

    Could you post an schematic of your implementation? It will make it easier to determine what may be going on. Thanks!

    Best regards,

    Jose Quinones

  • in reply to Jose Quinones
    Prodigy 150 points

    Hi Hardik,

    Could you post an schematic of your implementation? It will make it easier to determine what may be going on. Thanks!

    Best regards,

    Jose Quinones

    0070 003 Gubbels Engineering Mendel.pdf
  • Intellectual 840 points

    There seems to be a wiring problem.  On the ATMEGA644ATQFP44 pin 6 is shown to be tied to ground and should not be 2.46V

    Also Pin 6 and Pin 9 for all 3 DRV8811 show resistor and capacitor to ground.  The Datasheet indicates they are Bridge A blanking and off time adjust and Bridge B blanking and off time adjust. I would remove power and check the resistance to ground on both sides of the 220k resistors and to check that Ground for V+ is actually connected to the same power suply as the ATMEGA644ATQFP44 since a ' floating ' ground can cause this kind of issue as well as blow components.

  • in reply to hardik padhariya
    TI__Expert 7455 points

    Hi Hardik,

    Sorry I took so long to provide an answer to this post. The schematic looks good on the DRV8811 side, but there are a few things I can point out:

    1. The RC network has a resistor which is too big, I would start with something in between 12K and 47K. I am not certain what value the cap is, but if it is 220 pf, then that is too small. I would try something like 800 pf to 1000 pf.

    Have in mind that the TBLANK will be equal to 1400C. At 220 pf, your TBLANK is 308 ns. With such a slow time, it is possible for the current regulation to be triggering on noise, in which case you will never be able to get a decent current buildup.

    On the other hand, the resistor and the cap configures the TOFF with the equation TOFF = RC, which gives us 48.4 us. With a TIME OFF so large, the fastest frequency you can possibly have (if TON = 0s) is 20.661 KHz, which most likely will result in some audible noise as the TIME ON has to be something larger than 0s.

    I would try changing those caps and resistors and that may fix the problem. Let us know if that's not it.

    Best regards,

    Jose Quinones

  • in reply to Jose Quinones
    Intellectual 840 points

    I thought i recognized the schematic.  http://www.reprap.org/wiki/Generation_6_Electronics I highly recommend reading the full page and if you have an IRC ( internet chat ) program contacting the one mentioned on that WIKI.  If you purchased the board in question, the section admits that there has been issues so careful checking the board may resolve the issue along with doing your own calculations on each of the DRV8811 capacitor/resistor pairs at pin 6 and 9.

    Good luck with the project, mine is currently stalled trying to decide on how to do the x and z axes in wood.

  • in reply to Eric Blenner-Hassett
    Intellectual 840 points

    I was digging in the alternate electronics section and found that one of the other versions uses the same driver IC

    http://reprap.org/wiki/R2C2_RepRap_Electronics

    You may want to look in the schematics and see what they did to adjust the A4988 as this workaround most likely would apply to your situation for the DRV8811.