I have a PCB (let's call it PCB #1) that has a Li-ion battery as its power source, sourcing 12V to 17V. The power from the battery is used to step down to 6V using a buck converter on PCB #1. A cable connection sends the input power (12V-17V) to the second PCB (let's call it PCB #2). The 12V-17V is regulated to 12V using a non-isolated DC-DC converter. Both the 6V from PCB #1 and the 12V from PCB #2 are sent (using cables) to the third PCB, PCB#3.
Update: added the note regarding 5V DAC outputs.
A 5V DAC sends two outputs to the 12V circuitry (used as control signals for two HV DC-DC converter modules).
My question is whether the 5V return and 12V return on PCB #3 should be joined together? If I do join them, would that not create a ground loop?
Currently I have them separated and I have a copper pour for each. The 12V return is shown in the top image as light green; the 5V return is shown in the bottom image as dark green.
If they should be connected, should I:
- (a) simply join them together and instead of having GND-12V and GND-5V, I'll have GND?
- (b) join them at one spot using a low-impedance connection, i.e. using a 0 Ohm resistor or a jumper?
- (c) join them at one spot using a resistor? (I have personally never done this but it has been done)
- (d) join them together, but keep them separate with a slit in the ground pour/plane?
- (e) should I leave them as is, i.e. separate from each other on PCB #3?
Thanks in advance.