DRV8873: DRV8873HPWPRQ1 - nFAULT status unable to reflect updated status of Open Load with 12usec nSLEEP low pulse and nOL tied to low

Hi Subramaniam,

When the nSLEEP reset pulse is mentioned in the datasheet, it appears to be intended for the DRV8873S (SPI version) only.

Resetting the nFAULT may require entering/exiting sleep or power cycling.

We will contact the design team for confirmation. Please expect a reply by Jan 7th. 

Hi Subramaniam,

The design team has requested that I gather additional information, which I plan to do today.

Please expect the next reply by Jan 9th.

Hi Subramaniam,

I responded to you directly, but have found the following:

1) The nSLEEP reset pulse does clear an open load passive fault in the DRV8873H

2) The nSLEEP reset pulse also clears an open load active fault in the DRV8873H.

3) The open load active appears to be checked any time the low side FET is turned off.

The type of load used (pure resistive vs inductive) can affect operation in active mode. If the energy in the inductor does not create a voltage above Vola, the open load active fault will assert.

Dear Rick,

I have responded to your reply.

Further can you clarity the pulse width on nSLEEP pulse being 12uSec on the waveforms, from volt/div of 50us/div, with interpolation I understand it to be 12usec.

Also the device under test is it hardware version at your end, since you replied in last thread the only SPI version. Please clarify does the hardware version of the device requires to be sent to sleep mode to reset the nFAULT status?

Thanks and Regards,

Subramaniam

Hi Subramaniam,

Further can you clarity the pulse width on nSLEEP pulse being 12uSec on the waveforms, from volt/div of 50us/div, with interpolation I understand it to be 12usec.

Yes, the pulse width is ~12us. Please refer to section titled "nSLEEP Reset Pulse" and the figure titled "nSLEEP Reset Pulse". A pulse less than 5us does clear the fault, and a pulse greater than 20us may cause the device to begin to enter sleep mode.

Also the device under test is it hardware version at your end, since you replied in last thread the only SPI version. Please clarify does the hardware version of the device requires to be sent to sleep mode to reset the nFAULT status?

The device tested is the hardware version. Initially, I did not have the hardware version available.

The nFAULT status of the hardware device can be reset using the nSLEEP reset pulse (5us to 20us).

Assuming the DRV8873H-Q1 exits sleep mode with the outputs static:
If the device exits sleep mode with an open load, the open load passive detection will assert the nFAULT.
Connecting the load at this point does not clear the fault because the open load is checked when exiting sleep mode.
Sending the nSLEEP reset pulse will clear the fault, but does not re-check for open load.

When operating a pure resistive load the open load active detector may issue a fault if there is not enough parasitic inductance to cause the voltage to exceed Vola. If this is the case the nSLEEP reset pulse clears the fault once the load is no longer driven.