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DRV8301: Vds sense circuitry working

Shashank more
Intellectual 650 points
Part Number: DRV8301

I am using DRV8301 to drive a 800W BLDC motor.I wanted to know how Vds sense circuitry work? (I mean all the concepts like Vds sense sampling rate, sampling time and how Vds voltage value is determined?)

I asking about this because while using OCP my MOSFETs sometime TURN ON correctly but sometime do not!! (even if Vds is less than Vds trip point). So, I think if i know about Vds sense working then i would be able to select MOSFETs capable to work with OCP enabled.

This information is not given in the datasheet.

  • 0
    TI__Guru** 114905 points

    Hi Shashank,

    How are you using the VDS monitor? Please note section 7.3.4.1 of the datasheet.

    The VDS monitor is not intended for precise current regulation.

    VDS is monitored when the FETs are enabled. If the VDS is exceeded for ~1.5us, the fault will disable the FETs depending on the OCP_MODE selected.

    You can use current limit mode or report only mode as described in section 7.3.4.1 and monitor the nOCTW pin. This will help you determine when the VDS monitors triggered.

  • 0 in reply to Rick Duncan
    Intellectual 650 points

    Rick,

    Thanks for the reply.

    Lets take a scenario, suppose i give high input at INH_X or INX_L pin then the IC would give high output at GH_X (VDD+GVDD) or GL_X (GVDD). As you said if VDS is exceeded for ~1.5us, the fault will disable the FETs depending on the OCP_MODE selected.   So, my MOSFET should turn ON within ~1.5us if not then the fault will be detected because if MOSFET do not completely turn On then Vds would not be equal to ~ 0V, Vds would be greater than Vds trip value.

    I am using IRFP260N which have Turn-ON delay time = 17ns , Rise time = 60ns , Turn-OFF delay time = 55ns and Fall time = 48ns. These are in nano seconds!!!. So, my MOSFET should turn ON or IC should not give fault of OCP. But here IC is not turning mosfet ON and giving fault.

    Can you please explain why this is happening?

  • 0 in reply to Shashank more
    TI__Guru** 114905 points
    Hi Shashank,

    The FET timing parameters are only part of the timing. The GL_x and GH_x source and sink current settings of the DRV8301 affect the slew rate of the FET. This in turn affects the RDSon and VDS.

    It is usually best to monitor the nOCTW pin and work backwards in time using a scope. It is important to monitor the VDS at the pins SH_x with respect to PVDD1 and SL_x of the device. With the nOCTW pin, you can narrow down the cause of the fault.

    I suggest you try current limit mode, which will limit the current but not assert a fault. If you capture some scope shots, it should be easier to explain.