DRV8323: VGHx goes higher than spec

Hi Biter,

Thank you for posting to the Motor Drivers forum!

Would it be possible for you to share a schematic of you board setup? 

The DRV device's pre-drivers (for both HS GHx and LS GLx) are supplied by the charge pump, so it could be possible that the charge pump is setup incorrectly.

Best,

~Alicia

Hi Alicia.

Here you go.

Thank you very much!

Hi Biter,

Would you mind sharing your schematic in a pdf format so that it is easier to see all of the components?

Best,

~Alicia

40001110-4.pdf
Hello Alicia,

Here you go.

Thank you very much!

Hi,

biter terbi said:

As you can see the GH goes to 13.5V, which is out of spec for this driver:
(Vmax = 13.5V)

Saying GHx = 13.5v and out of spec is not quite correct without knowing the voltage at SHx pin. The driver output GHx such that (GHx - SHx) = 13v to turn on the upper FET.

Please post waveforms of GHx and SHx together.

Brian

Hello!

The waveforms I'm posting are measured from SHx to GHX, otherwise the voltage would be much higher.

Do you want me to measure SHx to GND?

Thank you!

Biter,

just to make sure we cover the basics, are you using tip & barrel measurement technique for collecting those curves?

biter terbi said:

Yellow is GH->SH and blue is GL->SL

As you can see the GH goes to 13.5V, which is out of spec for this driver

Max is 13.5v, and I don't see (VGH - VSH) more than 13.5v in the scope pic below -- less than the measured 13.4v; so why saying it is out of spec?

Also, most FETs have max Vgs at 19v, so 13.5v is nothing to concern as far as the FET, and the VCP is internally generated and so you don't have any control about it.

Brian

Hello Brian.

13.4V is pretty close to 13.5V, I'm burning drivers in a sporadic way. This is a very controlled measurement, it may not show what really happens when the motor is out in the street.

Also, 19V is the MOSFET's max, the driver can only hold up to 13.5V.

Please tell me your commets.

Best regards

Lenio,

Yes I am. I'm using those pigtails and also made a contraption with a coaxial cable to measure a little further from all the EMI the power stage emanates. I'll send you a picture tomorrow morning.

Thank you!

biter terbi said:

Even though my capacitors had the same values it seems they're a different quality.

Interesting, as I can't see how a "wrong" cap connected at VM and VCP can cause the upper gate VGH to be higher than 13.5v as the driver regulates this voltage to a typical 11v and 12.5v MAx, even though voltage at CPH-CPL can be 2x of VM.

What is your VM voltage?

Brian

I made a mistake, it was the capacitor between CPH and CPL, I'm sorry for the confussion!
Vm is 42V

Hi Biter,

I am glad that you were able to resolve the issue. I am going to close the thread for now.

If you have any additional questions on this topic, please feel free to reopen this thread.

Best,

~Alicia