I'm designing a general purpose Arduino shield pcb and right now I'm struggling to find a proper ground layout.
ICs on the board: 12->5V and 12->10V @5A switching DCregulators, several H-Bridge motor drivers (rated at a max 1.8A), a TEC driver (rated at max 3-6A ),a pair of octal-switch SPST, a pair of shift registers and a DAC among some op-amps, FETs and BJTs.
I'm following Ott's guide for grounding mixed signal pcbs. I've got the basics down, but the main issue is that the TEC driver's datasheets implies the existence of a Power Ground on the PCB and considering all the large currents flowing out of the DC regulators, I realize it can be quite relevant. I'm also not sure if the motor drivers should be part of this power ground plane (the 10V rail is supposed to power DC motors driven by the H-Bridges).
My questions: are the digital ICs (Shift registers, SPST switches, digital side of the DAC) really that noise sensitive that a noisy ground would compromise their behaviour? (I suspect only the DAC). If that was not the case, I could just use a common Digital/Power ground.
I'm considering a power ground (DC regulators, Motor drivers) with two bridges: to digital ground (SRs, Switches) to an analog ground (TEC driver), and additionall a bridge between the digital ground and a second analog ground (with the DAC and analog input pins). Would there be any ground loops with such a configuration?
Best Answer
Wow, Well we could spend hours discussing ground.
I'm not that much of an expert, but I have made lots of mistakes. First I would say there are two "ways" to think about ground. At low frequencies (DC to audio) the "star" ground concept is useful. Here I'll draw a picture, with big heavy lines for paths with a lot of current. And then bring all those separate paths to one point. (the point where power enters the circuit.)
The idea is to keep the high current's out of the more sensitive parts of the circuit.
At higher frequencies ~10 MHz and above, one starts thinking about a ground plane that is everywhere. With lots of ground connections between the case and the ground plane. At the higher frequencies on is not so much worried about the DC drop in the ground lines, but the inductance of the ground. You want the fast signal wires to have a (continuous) ground plane underneath them that carries the return current.
I'm sorry I haven't answered your question. Whether you have a loop or not depends on how you lay it out. And a small ground loop on a pcb may not be that bad.
The best thing is to build it and try it, and remember that you may have to "fix" the ground.