Ground plane under H-Bridge, or not?

[Mercury]

Hi guys,
I have 30V 50A MOSFET H-Bridge (at about 20kHz PWM), as well as a MCU with a 12-bit ADC on a 4 -layer PCB. The bridge is on the top layer and the MCU is on the bottom layer, but not directly under the bridge. The bridge will for sure generate disturbances which might influence the ADC. There are three routing scenarios that I'm considering:

- SPlit the ground layer into two regions, one for the bridge and one for the MCU. The regions would be connected at a single point
- Route the bridge in the top layer and the internal signal layer and run the ground layer underneath the bridge area
- Route the bridge in the top layer and the internal signal layer but the ground layer avoids the mosfet area

My PCB stack-up is Top, Middle, Ground, Bottom. So, what would you guys recommend me to do, in order to minimise the noise from the bridge?

George

 

[marce]

Without a fyull schematic I would not give an opinion, as that is all it would be, an opinion. In this situation I would examine all the data sheets and look carefully at my layout topology. These jobs are quite often the most painfull to lay out, but also the most fun.
On previous similar designs I have used on ground plane with some strategic slots to minimise stray current paths, and also had layouts where there was no grounds under any switching nodes (these were higher frequency where capacitive coupling was a concern).
Sorry to be non specific, but as stated these sort of designs can be finiky.