LMG3522R030: LMG3522R030 PCB layout kelvin connection problem

Morty Xu

Part Number: LMG3522R030
Other Parts Discussed in Thread: ISO7741

Hi experts,

Here is my customer's LMG3522R030 PCB layout, the kelvin connection between signal ground and Source of GaN is shown in the figure below:

use a trace to connect two coppers instead of vias like the EVM.

According to the previous layout experience of Si MOS, but not sure whether it is applicable to GaN HEMT.

The blue box is signal ground shielding layer, the red circle is the trace of kelvin to the bottom GaN Source.

The top GaN too.

over 1 year ago

0 Travis Williams over 1 year ago

TI__Expert 8960 points

Hello,

I'm having some difficulty understanding your question. Are you asking whether to use a trace or plane to connect your signal ground to the FET source?

Thanks,

Travis

0 Morty Xu over 1 year ago in reply to Travis Williams

TI__Intellectual 1620 points

Hello Travis,

I wonder if this is risky, the customer did not use vias connection for signal ground and FET source as in the GaN EVM board, but used trace instead.

Thanks.

0 Travis Williams over 1 year ago in reply to Morty Xu

TI__Expert 8960 points

Hello,

In this design, is the customer using a digital isolator on the fet shown?

Also, is this the low side or high side FET?

Thanks,

Travis

0 Morty Xu over 1 year ago in reply to Travis Williams

TI__Intellectual 1620 points

Hi Travis,

The customer uses ISO7741 and the high side and low side FET are the trace shown in the above picture.

Thanks

0 Travis Williams over 1 year ago in reply to Morty Xu

TI__Expert 8960 points

Hi Morty,

I recommend switching to using a ground plane instead of trace. This will substantially reduce signal inductance & EMI susceptibility. The digital isolator should ensure that common mode noise next to the FETs doesn't make it back to the analog ground of the circuit.

Ground bounce is almost unavoidable with these fast switching circuits, but the signals being well referenced to PGND should ensure that the digital signals bounce with ground.

Thanks,

Travis

Power management

Power management forum

LMG3522R030: LMG3522R030 PCB layout kelvin connection problem