DRV8704: Weird Gate driver behaviour

Hi Oleksii,

Let me do some research on your question and I'll get back to you within a business day.

HI Oleksii,

Apologies for the late reply.

Has this behavior been observed in more than one IC?

You mention in the linked post that the motor only works in one direction. Is this issue only occurring when driving in one direction?

Can you share the driver schematic?

More than one. Changed both driver and MOSFETs, nothing works. xOCP flag raised everytime Im trying to move motor - and its quite reasonable because all MOSFETs receiving ON signal. But why is that so - no idea

P.S. 470 uF capacitor on +Vm added while testing

Alex,

Thank you for sharing the schematic.

The schematics looks good to me. Although it looks like the switching node of each of the half-bridges is not connected to xOUTx node. Maybe it's not shown well on the schematic. I'm sure this is a diagram error but can you double check.

Can you measure AOUTx and BOUTx, nFAULT? Can you take another waveform showing A1HS, A2LS, AOUT1, nFAULT while AIN1=HIGH.

If the MOSFETs are not being enhanced properly, there will be high RDSon which would explain the OCP fault. Seeing the waveforms I requested below will give me a good idea if this is the case.

Yellow - nFault

Violet - A1HS

Cyan - A2LS

Green - AOUT1

Hi Alex,

Thank you for the waveform.

It looks like the high side FET begins to turn off when the command is given to turn off the low-side FET. This causes the RDSon of the high side FET to increase which increases the VDS and causing the OCP fault.

Is this same behavior also happening on the other half-bridge?

The next step is to understand why the High-side FET begins to turn-off. Can remove the FETs and retake the waveform (similar to the one you sent). However, instead of measuring OUT1, measure AIN2. I wonder if the FETs are somehow affecting the gate voltage.

That was channel B, here is in2 instead of out1

now,here is what I got on another channel

and only gates:

and diagram without MOSFETs

Alex,

Pablo is out of office today.  He will reply tomorrow.

Regards,

Ryan

Hi Alex,

Thank you for the waveforms. Is the waveform without the MOSFETs taken on channel A or B?

From the waveforms, it looks like only channel A is having the issue with the gate voltages. It could be the device is damaged. Have you tried replacing this IC with a new one? does that solve the issue?

That was channel B, channel A without MOSFETs looks exactly the same. It seems like this is MOSFETs issue...