For my boards, V5 and V6 - see my earlier board review post, are high performance designs, while V4 is the low cost design. The V6 brings back the mounting holes with 2x full M2 screw holes with many other improvements, at a higher price point. I’m not too interested in trying to make the high performance versions hand-assembly friendly as the reliability of hand assembled boards isn’t great in my experience, and it’s hard to hand assemble high density without accidentally knocking nearby components. But for the V4 boards they are low cost and hand assembly friendly (reflow oven needed), and I have successfully assembled many by hand, and the 8 layer version is within the $2 PCB special offer capabilities from JLCPCB.
RDSon current sensing abuses the fact that most MOSFETs (from well known brands) perform better than the stated tolerance. In my experience parts from Chinese brands don’t overperform and are therefore unsuitable for RDSon current sensing unless you use a per-unit calibration routine with an external current sensor. It also needs temperature compensation to remain usable, so you either have to put external temp sensors close to the MOSFETs or use a board design which acts as a heat spreader alongside the MCU internal temp sensor, meaning low cost goes out the window if you choose RDSon current sensing. Also due to the high voltages involved, building a discreet circuit around it requires using high voltage switches and a ton of passives, therefore is impractical with STM32 internal OPAMPs. There is only a limited selection of chips that can do it, some options are the DRV8323, DRV8353, 6EDL7141 and RAA227063. RDSon current sensing is usually less accurate than other current sensing methods like hall effect and resistor current sensing.
The reason I use RDSon current sensing is mainly because of the zero additional power losses with the additional benefits of easier layout enabling faster switching and less board space. I plan to do a more complete write-up of how RDSon current sensing works and an overview of my implementation once my V6 boards arrive and I implement the RDSon current sensing again as I’ve changed the MOSFETs from V5. I’ll probably post it to OSHWLab within the next 3 months.
Also regarding the split ground it’s generally not beneficial in most designs. The main reason is that high frequency current likes to follow the ground plane underneath, and with good ground plane it won’t spread much. But there are a few exceptions such as motor drivers with sensitive analog circuits, because of high magnitude low frequency currents close to DC, which will spread out across the ground plane and cause different parts of the circuit to see different GND potentials. In this case splitting the GND will block the big low frequency currents from reaching the sensitive analog parts. However, most motor drivers we design don’t have extremely sensitive analog circuitry that will be affected by this, so we can get away with a non split ground. And with multi layer heavy copper PCBs with big solid ground planes, the ground bounce can be mitigated significantly.
The reason I suggest removing split GND is because the split isn’t done correctly here, you need to isolate EVERYTHING between the two GNDs and can’t have signals crossing between them except at the point of the split.
Also I’d appreciate some more reviews of my V6 driver, currently I’m still waiting for JLCPCB to restock an inductor before I can place the order.