DRV8350: VDRAIN to VCP Waveform

Could you help on above thread question!

And also, one more question. Since customer has offered some system sample to end customers, and that cap connection is between VM and VCP.

We found there is a 45.5V voltage between VM to VCP. is there any risk in the device? thanks.  

Hi Brian,

Could you please provide your full circuit schematic? We believe that while there may be some normal dipping on VCP during startup, what is shown in the waveform isn't the most typical.   If you could also provide the waveforms on VM, VDRAIN, CPH/CPL that would be helpful too. 

Brian Wang0928 said:

And also, one more question. Since customer has offered some system sample to end customers, and that cap connection is between VM and VCP.

We found there is a 45.5V voltage between VM to VCP. is there any risk in the device? thanks. 

For this case, is VM tied to VDRAIN? The capacitor (VCP) should be from VCP to VDRAIN, not VCP to VM.  And VCP should rest typically 8-12V above VDRAIN and can reach an ABS max of VDRAIN + 16V.  If VM is low but VDRAIN is a very large value, as long as VCP stays within spec in relation to VDRAIN then there should be no problem. 

Please let me know if I can clarify anything further. 

Best Regards,

-Joshua

Hello Joshua,

Thanks. 

In this case, customer will take your suggestions to modify the schematic. However, before that they need to convince end customer why the circuit configuration needs to be modified. So Customer would like to know how come some pins could be damaged and become low impedance when cap is connected between VCP to VM pin.

So far customer mentioned they don't find any risk on the waveform even the input voltage is up to 60V during power on. Please see the tested waveform as attached file.  

VCP to VDRIAN Analysis.pptx

Regards

Brian 

Thanks. We still do not understand how the device was damage with some pins. are they related to the configuration of charge pump VCP-VDRAIN capacitor? if not so, what could make it happened?

Customer needs to offer more info. logically to explain to end user. Very thanks. 

Regards

Brian

Hi Brian,  

Thanks, let me look into this a bit more as to better help explain some of the potential causes and cautions.  

Best Regards, 

-Joshua

Is that possible please help on this questions! Thanks. 

Hi Brian, 

I apologize for the delay. 

From the information given I believe there may be other factors that are leading to the shorting being observed. The most likely cause is the voltage/current on VCP (I-VCP) is exceeding the maximum rated values. Can you please confirm that the voltage on VCP does not ever increase past the Abs-max value of VDRAIN+16V? And that the current, Ivcp, is as expected under these conditions:

There are not many reasons VCP would short outside of these violations. For thoroughness, can you provide the IDRIVE setting used as well as the full schematic? I would like to confirm there are no additional circuit component issues. 

Best Regards,

-Joshua 

Thanks.

Please find the ppt files as attached and find out the root cause possibly.

Very thanks.

DRV8350 Analysis_20231017.pdf

Regards

Brian

Thanks Brian, 

I notice immediately that the IDRIVE setting is set pretty high (450/900mA) and the fast switching may be putting additional stress on VCP. We actually recommend using the lower IDRIVE settings, so can you test the same setup/waveforms with IDRIVE set to 50/100mA (source/sink)? 

Also I notice that the supply capacitor DC13 is 4.7uF when we actually recommend >= 10uF, which may not be directly related to this but might be helpful to change for proper device operation.

Best Regards,

-Joshua