DRV8323: Current sensing over rds_on => SOx voltage anomalies at higher currents

Prodigy 210 points

Replies: 27

Views: 444

Part Number: DRV8323

Hi together,

I have some voltages anomalies at the current sense outputs of my design. I'm using the measurement over the rds_on (SH_x, SNx).

At higher currents the output goes to "0" (=3V) for 5µs, afterwards the signal ist back as expected. The phase current doesn't have these spikes, so the driver seem to work.

Spikes start at ~80A phase current.

Green is the voltage on SOB,

Red is the current measured with clamp meter.

The DIS_SEN =1b, so the fault is ignored. Is there another protection of the SOA output? Or can you explain what happen in these 5µs?

Rgds Martin

27 Replies

  • Martin,

    Is it possible for you to try a slightly smaller sense resistor?

    Regards,

    -Adam

  • In reply to Adam Sidelsky:

    Hi Adam,

    As I mentioned I'm using the rds_on of the low side mosfets for current measurement (2 parallel => rds_on 0.5mR) and I can't change to a sense resistor, because of the PCB space.

    Do you have an explanation for these "spikes", is this a known issue with the rds_on measurement?

    Rgds Martin

  • In reply to Martin Fuchs7:

    Hi,

    Are there any updates on this issue?

    Rgds Martin

  • In reply to Martin Fuchs7:

    Martin,

    It's hard to say exactly what is causing the spikes but I can tell you that using the FET RDSON for current sensing is not usually recommended. The RDSON from one FET to the next can change quite a bit and the RDSON also varies with temperature.

    Have you checked if you are violating the input max or min for the CSA input?

    Regards,

    -Adam

  • In reply to Adam Sidelsky:

    Hi Adam,

    The problems with the RDSON are known and compensated in via software. I didn't find any information, that RDSON measurement isn't recommended with the DRV8323 Driver.

    I checked the CSA input voltages and they are within the spec values.

    Rgds Martin 

  • In reply to Martin Fuchs7:

    Martin,

    Did this issue get resolved? Sorry for the delay here.

    Regards,

    -Adam

  • In reply to Adam Sidelsky:

    Hi Adam,

    For me it's no really resolved. I still have no answer to the questions:

     "... Is there another protection of the SOA output? Or can you explain what happen in these 5µs?"

     Rgds Martin

  • In reply to Martin Fuchs7:

    Martin,

    Have you checked the status of the VREF/VM supplies at the time of the 5us dip? Are you using the SPI or hardware version of the device?

    Regards,

    -Adam

  • In reply to Adam Sidelsky:

    Hi Adam,

    I'm using the SPI device. The VREF/VM are ok, the phase current is still flowing during the dip.

    By the way: on the revision history of the index *c* data sheet is no information, that the mechanical data has changed.

    Rgds Martin

  • In reply to Martin Fuchs7:

    Martin,

    Are you reading or writing any SPI signals when the dip is seen?

    What about the CAL pin during the dip?

    Can you share your schematic?

    Regards,

    -Adam