DRV8323: High Side switching causes interference on the Low Side

Josef Alt

Part Number: DRV8323

Hi,

when my customer switches the high side Fet the Gate on the low side fet shows interference. This is also at low IDRIVE values. (Measurement picture below with 30mA IDRIVEP and also low IDRIVEN). With higher IDRIVEP the interference much more bigger.

For the low side FET my customer can increase the IDRIVEP and IDRIVEP and saw no interference by switching..

After layout finished, they were adding a 1µF bypass capacitor between Vin and GND but this did not have any effect.

In layout (pictures available in private session) they realized that the layer under the Vin Pad from the Hide Side FETs is GND potential.

=> Could the issue a capacitive coupling between the Vin and the GND plan under the high side FETs?

=> Any ideas what can be done to reduce the interference?

Thanks

Josef

over 4 years ago

0 Anthony Lodi over 4 years ago

TI__Mastermind 26656 points

Hi Josef,

It is possible that there is some dv/dt coupling through the Cgd capacitance of the low side MOSFET as the high side source switches on. It does seem to be related to the slew rate of the FET since you mentioned that the issue is much worse at higher IDRIVE settings. Another possible source could be ringing on the SPx node of the sense resistor that is coupling in through the Cgs capacitance of the low side FET. If this is the case, a capacitor can be placed from the high side drain to the low side source to help reduce this.

Is the yellow trace showing the high side gate to ground voltage? Or is it showing the high side source to ground? If the yellow trace isn't the high side source to ground voltage, would the customer be able to provide a plot showing the high side source to ground voltage along with the low side gate to ground voltage? I want to see if there is significant ringing on the high side source that could contribute to the issue. Additionally, would the customer be able to provide a plot showing the SPx to ground voltage of the sense resistor to see if there is ringing on that node?

What MOSFETs is the customer using? I am primarily curious to figure out the Qgd of their MOSFETs. What PWM mode is the customer using? In 6x, 3x, and 1x PWM mode there is a strong pulldown current on the low side gate when the high side gate is switching to help avoid dv/dt coupling, however this feature is disabled in independent PWM mode.

Regards,

Anthony

0 Martin Komander over 4 years ago in reply to Anthony Lodi

Prodigy 40 points

Hello Antony,

the yellow diagram is the Gate von the high side FET.
The source,... measurement I will upload the diagrams after measurement.

The used mosfet is the
Vishay SIR870ADP-T1-GE3
https://www.vishay.com/docs/63657/sir870adp.pdf

In SW we use the 1xPWM mode.

1µF Capacitor high side drain to the low side source shows no effect.

yellow: high side drain to GND (24V)
red: low side gate to GND
blue: high side source to GND

Thanks for support an BR

0 Martin Komander over 4 years ago in reply to Martin Komander

Prodigy 40 points

The SPx measurement on Phase A

left rotation:

left rotation zoom in:

right rotation:

right rotation zoom in:

0 Anthony Lodi over 4 years ago in reply to Martin Komander

TI__Mastermind 26656 points

Hi Martin,

Thank you for the waveforms! based on the duration and amplitude of the ringing on the SPx node this seems like it could a result of an issue with the layout of the board. It could be an issue with high inductance in the ground path which is causing ground ringing. Would you be able to provide your schematic and layout for me to review? If you can provide it to Josef I will reach out to him privately over email.

Regards,

Anthony

0 Matt Hein over 4 years ago in reply to Anthony Lodi

TI__Mastermind 21805 points

Hi Martin,

Do you still need help on this thread?

Thanks,

Matt

0 Martin Komander over 4 years ago in reply to Matt Hein

Prodigy 40 points

Hello Matt,

it would be nice if you have any idea for this issue.
I'm already in contact wil Anthony.

Thanks and BR
Martin

0 Matt Hein over 4 years ago in reply to Martin Komander

TI__Mastermind 21805 points

Hello Martin,

Let me get with Anthony on the latest and see if I can provide any additional assistance.

FYI - The team is on holiday due to Memorial Day in the US.

Thanks,

Matt

0 Anthony Lodi over 4 years ago in reply to Martin Komander

TI__Mastermind 26656 points

Hello Martin,

As we have been discussing over email, it seems like there may be a grounding issue on the layout that could be the cause of the voltage spikes you are seeing. I will reach out to you over email regarding a test for you to perform as we try to work towards a solution. I will talk to Matt about the issue to bring him up to speed on where we are at.

Regards,

Anthony

0 Martin Komander over 4 years ago in reply to Anthony Lodi

Prodigy 40 points

Hallo Anthony,
thanks for supporting. I'm on vacation next week. But if you will send me the test I would like to make it 14. June.

BR
Martin

0 Anthony Lodi over 4 years ago in reply to Martin Komander

TI__Mastermind 26656 points

Hi Martin,

I apologize for not sending out the test sooner, I will aim to send it to you over email today. I hope you have a great vacation next week!

Regards,

Anthony

0 Matt Hein over 4 years ago in reply to Anthony Lodi

TI__Mastermind 21805 points

Hi Martin,

Is there further assistance that you need on this thread?

Thanks,

Matt

0 Anthony Lodi over 4 years ago in reply to Matt Hein

TI__Mastermind 26656 points

Hi Matt,

We are continuing to work on this offline over email.

Regards,

Anthony

0 Matt Hein over 4 years ago in reply to Anthony Lodi

TI__Mastermind 21805 points

I'll close this E2E thread since the discussion has moved to email.

Thanks,

Matt

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DRV8323: High Side switching causes interference on the Low Side