Part Number:DRV8701
Hi,
I have been having a few issues with the MOSFET failures that I believe Vref should be protecting against.
Setup:
-24V 24.5A BDC Motor
-24VAC toroid rectified to 34VDC high current supply
DRV8701 Specs:
-0.005 Ohm 5W Rsense
- 3.0 Vref (30A = 5V / 20*0.005)
-Idrive = 100/200
Failure:
Motor runs a few times and then eventually one of the MOSFETS semi-conducts constantly.
Generally it is a high Side MOSFET that fails. Replacing the MOSFET and lowering the Vref by half generally allows it so I can run, but it eventually fails again. Replacing only the high side MOSFET will allow it to work again but fail quickly. I need to replace all 4 MOSFET's and it will operate for a longer duration but eventually fail again.
I've tried multiple different MOSFET's with different specs (all Vdss = 60V+ and Id=70A+) and experience the same failure. I have a feeling the back emf is the cause of the problem but I'm not sure how to go about handling it.
I've included my schematic and layout. Note that the motor driving circuit shows I have flyback diodes but those currently footprints on the PCB. I have not physically added them as per the DRV8701 datasheet.
Any advice is appreciated,
Mat
