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DRV8801: VpropI conversion factor off

Corentin BAZILLE
Prodigy 40 points
Part Number: DRV8801

Hello everyone !

I am currently working on integrating a DRV8801 into a design for driving a low-impedance, brushed DC motor at around 12V. I would like to use the VpropI output to get current readings but I have been unfortunate in doing so.

I have followed the data sheet's recommended RF filter at the VpropI output and am reading it with an ADC. The value I am reading is correctly converted from ADC to voltage value ; but once I divide the voltage by 5 to get the current value (since VpropI = 5 x Iwinding), the value I get is about 20 times bigger than the actual current value.

For instance, using an Rsense of about 24 Ohm (current limit at about 21mA) and using a 940 Ohm resistor between OUT+ and OUT-, the reading I am expecting is around 13mA. My power supply shows I'm using 15mA, and the ADC reading I am getting, by reading the voltage at VpropI (1.509V) and dividing it by 5 (0.3018V), is exactly 20 x 15mA...

I hope I am clear. Am I missing something in the datasheet ?

Thanks a lot in advance, any help is welcome.

  • 0
    TI__Mastermind 37683 points

    Hi Corentin,

    Thank you for posting to the motor drivers forum.

    Let us do some researching. Expect a reply by 10/14.

  • 0 in reply to Pablo Armet
    TI__Mastermind 37683 points

    Hi Corentin,

    The VIPROPI=5xI_winding formula that's on the datasheet is correct. If the current through the load is 12mA, the VIPROPI voltage should be around 60mA unless the device is damaged or VIPROPI is shorted to another supply. Are you using our EVM or your own board? Did you observe the same error with other units or boards?

  • 0 in reply to Pablo Armet
    Prodigy 40 points

    Hello Pablo,

    Thanks a lot for your quick response.

    I am indeed using a breakout board I have put together, together with a setup on a bread board. I cannot seem to locate any shorting on VpropI or anything that would indicate I am offsetting that reading in any way (although I have noticed that, when the load is not being driven, VpropI does not read exactly 0).

    Unfortunately, due to another factor (the device does not seem to detect power supply shorts under about 11V), my team has deemed the device unfit for our application and we have moved on to another device. Out of personal curiosity, I will try to further investigate this question by putting together another breakout board and try to see if I am seeing a gain of 5, but I cannot give you a clear answer for at least a few days.

    Please accept my apologies for opening this subject without being able to help understand what is happening for now.

    Best regards,

    Corentin

  • 0 in reply to Corentin BAZILLE
    TI__Mastermind 37683 points

    Hi Corentin,

    I understand. Please keep me informed on the findings of your test.

    If you would like to keep testing the DRV8801, we have a DRV8801EVM evaluation board which will be better than using a breakout board.