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DRV8302: Wrong current measurement

Thilo Binder
Prodigy 170 points
Part Number: DRV8302

Hello,

now my Motors work fine with my DRV8302 application, but the current measurement varies with the  change of the operation voltage.

Example: with  24V Operation Voltage, the device switches off  when   current increases  above 15A (Potentiometer adjust  on  OC_ADJ -Pin ) . With the same adjustment and 30V Operation voltage, the device switches of above 11A. The measured values on  SO1 and SO2 are also wrong. . I double checked the correct wiring and refered to the design in DRV 8302 Datasheet. What can be wrong there?

Regards

Thilo

 

  • 0
    TI__Guru 62730 points

    Thilo,

    Thanks for posting on the MD forum!

    Could you please share your schematic?

    You mention that SO1 and SO2 are wrong, what values are you measuring and what values are you expecting?

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 170 points

    Hello Adam,

     

    i made the tests without commutating the motor, because i cannot work with high currents with a rotating motor under laboratory conditions. (Maybe that is the mistake?). In my example i have the following conditions:

     

    Q5: PWM, Q6 inverted PWM, Q2 always on.

    Result:

    30V supply voltage, PWM adjusted to 15A supply current:

    SO2: 1,08V DC (0 A Voltage is 1,6V)

    SO1: Pulse similar to PWM above 1,6V, Vpp: 1,36V

     

    24V supply voltage, PWM adjusted to 15A supply current:

    SO2: 1,12V DC (0 A Voltage is 1,6V)

    SO1: Pulse Similar to PWM above 1,6V, Vpp: 1,24V

    I expected always the same voltages , because current is always the same.

    Or did i understand something wrong?

    Regards

    Thilo

     

     

  • 0 in reply to Thilo Binder
    Prodigy 170 points

    Shunt resistor value: 0.002R

  • 0 in reply to Thilo Binder
    TI__Guru 62730 points

    Thilo,

    To me these results seem fairly similar especially given the potential error of the CSA, the variance of the sense resistors, the variance of the board parasitics and similar.

    With very small sense resistance it's fairly common to have difficulty measuring small currents (15A small as compared to 100A which this small sense resistor is usually used for).

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 170 points

    Ok,

    i'll  try to compensate this by Software.

    And thank you very much for the quick Response in those troubled times.

    Regards

    Thilo