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DRV8350F: Separate VM from VDRAIN for STO SIL2

Part Number: DRV8350F

Hi,

I have an application, where I need SIL2, that means one safety channel is required. I use a STM32F7 with integrated

safety features, compatible to SIL2 and now the safety channel needs to be designed together with the DRV8350F.

From the datasheet it is possible, to separate VM and VDRAIN, that means, I can disconnect VM to disable the gate power

for the MOSFETs, but there I have some questions. When VM is disconnected and VDRAIN has still power, are the

gate voltages pulled to GND? Further, can I use a PMOS to disconnet VM from VDRAIN to implement a STO and if so,

what is the current raiting for VM?

Kind Regards,

Sebastian

  • Hi Sebastian,

    Yes you can power VM and VDRAIN independently. 

    There was a similar question a few weeks ago that you may find interesting, I'll link it here

    As for what happens if VM is disconnected and VDRAIN still has power:

    If at any time the input supply voltage on the VM pin falls below the VVM_UV threshold OR voltage on VDRAIN pin falls below the V VDR_UV, all of the external MOSFETs are disabled. This is gone over in the post I linked.

    As for the max current rating for VM, I found this on the datasheet. This is assuming a nominal power up of VM = VDRAIN = 48V

     

    I hope this answers your questions. Please let me know if there's anything else I can assist you with.

    Thanks,

    Michael

  • Thank you, good to know that.

    So I tought about something like this for a STO:

    Do you think one STO channel can be designed like this? 

  • Hi Sebastian,

    Generally we can not review schematics outside DRVx. However the logic you have implemented in this schematic does look correct. Once PWR_EN goes high then the PNP FET will turn off power to VM. I'd recommend simulating this.

    Best,

    Michael