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DRV8816: DRV8816 strange voltage shape of voltage over R SENSE

Wojciech Trocinski
Prodigy 20 points
Part Number: DRV8816
Other Parts Discussed in Thread: DRV8801

Hallo!

I am using DRV8816 EVM to test the DRV8816 motordriver IC. I want to use the VPROPI pin to control the current through the motor ( i know that it is not measuring anything during fast and slow decay). I have added a RC filter (6k2 1nF) and disconnected the on-board MCU to use my Synergy s124 for generating PWM (20Khz). The vpropi signal however was far from block shape of the PWM. I wanted to see how much influence the motor has on the signal so i replaced it with a resistor. The measurments can be find on the picture.

upper signal - VPROPI

lower signal - R SENSE

VPROPI cant keep up with the PWM, i blamed the build in opamp but i also measured the voltage across R SENSE and its not a block either. Could someone explain to me what is causing that delay?

  • 0
    TI__Guru** 114905 points
    Hi Wojciech,

    Can you provide a little more information?

    What resistor value was used when you replaced the motor with a resistor?
    Is there any capacitance on the the outputs?
    Is the lower signal (R SENSE) measured at the output of the SENSE pin?
    What is the value of the SENSE resistor?
  • 0 in reply to Rick Duncan
    TI__Guru** 114905 points
    Hi Wojciech,

    It has been some time since we last heard from you. We are assuming you have resolved your issue, and are closing the post.

    If you need further assistance, please reply to the post or select "Ask a related question" if the post is locked.
  • 0 in reply to Rick Duncan
    Prodigy 20 points

    Hi,

    Firstable i would like to apologize for the late anwser. I solved my problem but unfortunately found a new one. The non-ideality of the voltage measured on R SENSE was caused by inductance of the resistor that i was using to replace the motor. No i am using a low-inductance resistor and the voltage measured across R SENSE is a block as i expect it to be. However the VPROPI signal is still far from wat i want it to be, it still has the same shape:

    (Upper signal = VPROPI, lower signal = filter output)

    I decided to remove the filter. This is vpropi now:


    (VPROPI)

    It seems that my filter is causing the problem, but why? First problem is that the 3db frequency should be higher than it is now but why is the VPROPI signal (signal infront of the filter) so odd? My first tought was that it is maby caused by internal resistance of VPROPI?

    Could you maby provide some more informations on the VPROPI circuit? The datasheet of DRV8816 doesn't say much about it.

    Kind regards!

  • 0 in reply to Wojciech Trocinski
    TI__Guru** 114905 points

    Hi Wojciech,

    Please refer to the post: 

    The VPROPI circuit of the DRV8801 and DRV8816 are very similar.

    We will include this explanation in a future datasheet edit.