So I am doing a layout for a 4 layer PCB 1 ounce/layer. The Chip supports up to 20A (motor controller driver). The application needs about 12 amps max ( I plan it let it go up to 17A in the event of failure, controller force shutdown at 15A. In theory it should shuts down gracefully instead of just burning the trace out)
If I let it go up to 105 degrees (so 25 + 80) the trace width is 167mil on a single outer layer and 434 on a single inner layer as indicated by https://www.4pcb.com/trace-width-calculator.html
I am going need to separate the grounds between micro-controller and the Motor input (motor is noisy, I can't control that.) I was thinking, should run 85 mil on top and bottom traces, and 217 mil on the 3.3v and GND plane for the return current. (Rest will be poly-filled 3.3v for the power plane and board ground GND plane.)
The two ground planes will be tied together with a ferrite bead. Is there any downside to using 217 mil on both 3.3v and board ground layers? Or should I do a 434 mil on the power layer and leave the ground uniform board ground? Or any other suggestions?
The heavy outline is the chip (not exact same model but similar spec, I cant find an exact one with schematic, this one has more features.) So it goes from VCC -> HSA -> LSB -> GND or VCC -> HSB -> LSA -> GND depending on the direction of the motor. It's two half bridges.
I have no control over the FETs in the chip itself - it’s all built into the driver chip. Remember, the outline itself is a driver chip; I have no control over what is used on the inside. So what I have is battery (Vcc) to the diver, and it gives me outA, outB, gndA, gndB. The PWM isn’t in the wrong place, it just shows it as an input in that diagram. I think the lower FET in that diagram is telling the user how to wire for reverse battery protection. So the current goes from battery -> (into PCB) to chip -> (on pcb) HSA -> (off pcb to) motor -> (on pcb) LSB -> GND (out back to battery.)