DRV8847SEVM: DRV8847S nFault Pin

Hi Rui,

How are you testing the undervoltage lockout?
Is it possible the voltage is dropping below the UVLO supply falling level and then rising above the UVLO supply rising level? This would cause the nFAULT to assert and de-assert?
Are you monitoring the nFAULT bit with a scope? If not, please confirm nFAULT with a scope.

Hi Rick,

I used a scope to monitor the nFAULT pin.

I turned down VM power supply from 12V to 1V, sometimes the nFAULT pin wasn't pulled down, sometimes the nFAULT pin was only pulled down for a short time and then restored high level.

Thanks a lot!

Hi Rick, 

I test DRV8847S UVLO protection today. I find that when VM voltage down to 2.569V, nFault pin turns down.

However, when VM voltage down to 2.3V, nFault pin turn up again.

I think when VM voltage down to 2.3V, DRV8847S stop working, so MOSFET cannot work to drive nFault pin down.

DRV8847S UVLO function can only work between 2.3V and 2.569V, is it right?

Thanks!

Hi Rui,

Thank you for the additional information.

We are investigating the operation as VM continues to drop, and should have a reply by Tuesday.

Hi,

The UVLO voltage range is only 2.3V to 2.569V. If voltage fast down to 2.3V, the nFault pin will not go down,  which means UVLO protection not work.

It may not  supply efficient UVLO protection in customer circuit. Will we improve UVLO protection of DRV8847S?

Thanks a lot!

Hi Rui,

There are no plans to change the UVLO circuit of the DRV8847.

We have provided the customer comments to the team for future designs.