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DRV8402 for stepper motor drive

maxthestork
Intellectual 390 points

Hi All,

 

 I hope I am in the right section for this post.  I intend to use the DRV8402 in a stepper drive application where the stepper current will be around 3.5A per phase.   I was curious about the inclusion of inductors in the datasheet discussion and the EVM.  Why are they needed and more specifically would they be needed when driving a stepper that would have 2.65 mH per phase.

 I intend to configure the DRV8402 in full bridge mode. Would I be able to place a current sense resistor in the GVDD _B and GVDD_C lines to control the current in the stepper motor.

 Apologies if these sound like really dumb questions.  Please let me know what further details would clarify the question.

Cheers!

Peter

  • 0
    TI__Guru**** 189401 points

    Hi, Peter,

    Yeah, you got the right forum.

    The output inductors are used to limit the current into our IC in case the outputs are shorted. Without them, our output current limiting won't work, and you will let the magic smoke out of our IC (eg, it will be fatally damaged).

    You can sense current -- I need to find the reference schematic for that. I will post it later today.

    -d2

  • 0 in reply to Don Dapkus
    Intellectual 390 points

    Hi Don,

     

     thanks for the reply.  Yes the magic smoke, sadly I know it well.

     Do you think there is any specific reason for the fact that there is no mention of stepper motors in the datasheet or promo material.  Most times, steppers are mentioned in the possible apps with H bridges.  Just curious.

    cheers

    Peter

  • 0 in reply to maxthestork
    TI__Guru**** 189401 points

    Hi, Peter,

    No, we just left that out. It will work just peachy for steppers. The designers get mad at me when I tell them they're just designing high-current buffers! LOL.

    -d2

  • 0 in reply to Don Dapkus
    Intellectual 390 points

    Hi Don,

     not often that marketing miss a chance to claim something! 

     High current buffer is not very glamorous but while the DRV8402 is a very elegant design, it'd be hard to describe it better in 3 words.

     Were you able to find the schematic suggestion for current sensing in a stepper type app?

    cheers

    Peter

  • 0 in reply to maxthestork
    Intellectual 390 points

    Hi All,

     can anyone comment on the best way to hook up the DR8402 to sense the current delvered to the load?

     Don, did you have any luck finding the schematic?

     

    cheers

    Peter

  • 0 in reply to maxthestork
    TI__Guru**** 189401 points

    Hi, Peter,

    Attached is a drawing that shows how to sense the current --> note, you need to keep the voltage drop across the sense resistor to be less than 0.3V, or you may cause problems with the IC.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 30 points

    Hi Peter, Don,

    We currently use IR2104 and IRF540 FETS in all of our present stepper drives. we just came across the DRV8402. The specs sure look very promising.

    Don, You mentioned that the voltage across R_sense should not cross 0.3v. is it an absolute limit or more like the safe limit? I'm asking coz currently we use two 0.1 Ohm 5 watt resistors in parallel as our sense resistors for each full bridge. So using the same sense setup considering the 0.3V limit you suggested the drive can go up to 6A. Will this setup be able to work flawlessly at 0.3v or do we have to stay 5 or 10% below 0.3v for flawless operation?

    Also according to the datasheet the Recommended Max continuous Power per output pin is rated at 5A. However the Absolute Max current rating per pin is not given. Most steppers we use are rated at 5.5A. So will the IC be reliable at 5.5A?

    Peter, Have you completed the project? Hope you could share with us your experiences using the DRV8204 in Stepper applications.

    Joe!

     

     

  • 0 in reply to Joe Prince Francis
    Intellectual 390 points

    Hi All,

     Appologies for taking so long to reply.

     Don, thanks for the info.  Hope to be able to use it sometime.

     Joe, we eventually used an Allegro chip with external mosfets mainly because the currents we wanted to be able to drive at max headroom was around 6A.  Was not sure the DRV8402 would give us enough headroom.

     Was also a little concerned about the heat at 5A as it was for a portable device app.

     All the best!

     

    Peter