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Topic: connecting vss to gnd? (Read 860 times) previous topic - next topic


G_M is right about the Star connection, the best way to avoid ground loops, the way
to connect muliple loads together.

On a single pcb with both uC and h-bridge, use 2 power input points on opposite sides
of the board. Connect h-bridge power on one side and uC power on the other. Use a
"single ground trace" only to connect the 2 sides together. It needn't be super wide, as
it will be carrying only minimal current. This trace will provide the return path for the
current-sense resistor ckt, so you needn't add any extra ground traces/etc.

If you ever want to power both sides using only one power source [may or may not work
well, due to motor noise], connect it to the h-bridge side to keep the high current flows
on that side of the board.


Ok, so just one connection between the two, but is there any importance as to where that connection should be? I basically have two separate ground planes separated by a few millimeters,  i can add maybe a 16mil trace anywhere? Like middle or top
should I try and keep it closer to the circuit that needs the ground or should it not matter?


Even though I said there won't be much current in the "single" gnd trace connecting
the 2 sides, I always use 50-mil traces for grounds. Limits the trace resistance, and you
never know when someone will hook up the power on the wrong side, and pass 2-Amps
through your little 16-mil fuse [umm, trace].

You probably want the single point gnd connection located near to the 2 points where
the external power sources connect to the bd. This way any motor noise will not be
passing through all the rest of the onboard circuitry.

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