DRV8701: E: nFAULT pin active 1ms when turning bridge ON or OFF

Erik 6023585

Part Number: DRV8701

Device: DRV8701E

When the bridge is activated or deactivated the nFAULT pin is pulled low for approximate 1ms before returning high.

When changing duty cycle or direction, no fault is indicated. No current limiting is in effect since no current chopping is indicated and the fault would be approximately 3ms long, (t-RETRY).

when looking for a potential problem I noticed a strange behavior on the VCP pin. When the H-bridge is disabled the VCP is at 11.2V, but VM is 12V. When the bridge is activated it quickly builds to 21.2V and dropps down to 11.2V when turned off again. Is this a normal behavior? The device is not put in SLEEP mode. UPDATE: The device IS put in sleep mode. Se further posts.

over 5 years ago

0 Erik 6023585 over 5 years ago

Prodigy 235 points

UPDATE:

I captured some more scope images regarding the observation.

It seams that the sleep signal is used (wrong spot on the PCB was probed) and thus the fault at activation is a result of the VCP < V CPUV I presume.

Below capture:
Y: Enable B: VCP P: PH G: nFAULT

But when disabling the H-bridge the fault is triggered again according to: (Same color coding as above but going from 100% duty cycle to sleep)

I could not see a reference in the datasheet about how to put the device in sleep, must the EN be pulled low before SLEEP? Could this be the cause of the fault at turning off the driver? (See below update.)

UPDATE:
The fault is flagged even if EN is low when sleep is activated or disabled. What could cause this?