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Valued Contributor III
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Grounding recommendations

Hello. I am using the Cyclone III FPGA starter board and a Terasic THDB-HTG breakout board for interfacing to my circuit. I would like to know what is the recommended way to ground this board. My circuit is chassis ground referenced. Right now I have a chassis ground wire running from a screw mounted to the standoff mounting hole on the starter board. Any tips? Thanks

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Valued Contributor III
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Before you power anything up, just measure make sure the two ground planes (your circuit and the dev board) are truly at the same potential. Otherwise, I foresee smoke and a little hole in that little Cyclone III. 

 

Is your circuit going to be powered seperate from the dev board? That presents a different set of problems. 

 

Jake
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Valued Contributor III
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Hi Jake. Yes the grounds are all at the same potential. My circuit is powered from separate supplies - but all ground related, tied back to the chassis. Is that going to be a problem? __Dave

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Valued Contributor III
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Earthing is a complex question and you should check my recommendations, as I give no warranty. You have safety & EMC to consider. I think: 

 

1) Connect your power supply 0V to Chassis in one place. If you have more than 1 you'll get earth loops; if more current flows down one connection then another, or if you have a bad connection that is resistive, you'll get a local rise in the GND voltage. Bad for signals. 

 

2) Do above close to the power supply. Your power supply outputs may be floating and often 50Hz and other frequencies will be present in both the +ve and 0V outputs; so you won't notice them in your circuit as they cancel out. But for EMC, and if you have signals coming from outside this is bad as they'll are referenced to Chassis Earth and will see the rippling 50Hz (or other ripple). Referencing earth to 0V near the power supply ensures those ripple's are killed close to the source and don't make EMC problems.  

 

3) Use a star topology for connecting your power supply to different boards, or groups of circuits. If you daisy chain your power, and have hi power consuming circuits at the end of the chain, everything between them and the power supply experiences the current ( and noise) they generate at their 0V and +ve references. 

 

4) Keep reference 0V away from power 0V. If you have analog references, wire these separately to the best source of 0V reference (usually power supply), keep the wire clear of the power carrying leads and the local variations of GND they make because of high current and resistive connections, solders, crimps, etc. 

 

I'm sure other people will add to these. 

 

Brent.
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