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DRV8840: FAULT

Stephen Burns
Prodigy 10 points

Part Number: DRV8840

We are using the DRV8840PWPR in one of pcb assemblies.  If an overcurrent condition is created will the Fault pin stay at a logic low until the power is cycled to the VM pins? Note our Reset pin is pulled high so I can't issue a reset from the micro.  I am trying to test this scenario by intentionally creating an over  current condition but, I think its the over temperature fault thats occuring because it will go back to working after it cools down.  If I am correct, I believe the device will recover automatically from an over temperature condition but not from an over current condition.  Also, I do have the Sleep pin connected to the micro, but according to the data sheet I don't think that will make it recover from an over current condition.

 

  • 0
    TI__Genius 9800 points

    Hi Stephen, 

    Thank you for asking your question.

    The device has undervoltage (UVLO), overcurrent (OCP ) and overtemperature (TSD )protections. 

    The nFAULT remains low when OCP happens and it will be cleared if either nRESET pin is applied, or VM is removed and re-applied.

    For TSD and UVLO, the nFAult will be release when temperature goes below the safe level, and VM rises above UVLO threshold. 

    The nSLEEP low will put device in low power mode and disable H-bridges, gate drive charge pump and V3p3OUT regulator. 

    1- How the nRESET is pulled up? Is it pulled up to V3p3OUT, if yes, when nSLEEP goes low, it will disable the regulator and nRESET goes low too. 

    2- How the OCP is created? 

    Regards

    Mojtaba

  • 0
    Prodigy 10 points

    The RESET pin is pulled up through a 10K resistor to 3.3V.

    I have tried creating an overcurrent condition in two different ways.

    1.  This application uses a rotary actuator to rotate a valve open / close.  I install a valve that is too hard to rotate within our current limits.

    2. I install a jumper to short the output drive. 

  • 0 in reply to Stephen Burns
    TI__Genius 9800 points

    Hi Stephen, 

    Thank you for the update. 

    Stephen Burns said:
    The RESET pin is pulled up through a 10K resistor to 3.3V.

    Is it external LDO or it is taken from the 3p3OUT oin?

    Stephen Burns said:
    1.  This application uses a rotary actuator to rotate a valve open / close.  I install a valve that is too hard to rotate within our current limits.

    Device has current regulation which is set by ITRIP, if the BDC is stalled it will regulate the current at ITRIP. 

    Stephen Burns said:
    . I install a jumper to short the output drive. 

    Are you shorting the output to GND?

    Could you please capture, nFAULT, nRESET, OUT1, load current waveform when you short the outputs, 

    Best

    Mojtaba

  • 0 in reply to Mojtaba Afshar
    Prodigy 10 points

    The RESET pin is pulled up to an external LDO not the V3p3OUT pin.

    I am not shorting it to GND.  I am shorting OUT1 to OUT2.

    I believe you have answered my question which is;

    If I have an overcurrent event then the nFAULT will go to a low state and remain there until I cycle power to the VM pin.

    I believe my testing is only creating an overtemperature fault because my pcb does not provide enough heat sinking capability to allow time for the overcurrent fault. Every time I create a fault condition, it clears itself and goes back to working without me cycling power to the VM pin.  The nFAULT pin only stays in the low state for brief period of time. Note this is not a problem.

    We do monitor the nFAULT pin with the micro.  I just need to be able to instruct the user to cycle power if and when we actually do create an overcurrent condition.

    Thanks for your help!