Chassis Gnd connection
I need some help with grounding approach and the TVS diode connections.
Chassis-GND PCB-GND Bonding
I am currently tying PCB GND to Chassis_GND using a 100 Ω resistor + 0.1 µF capacitor + ferrite bead in paralleL.
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Is this RC + ferrite arrangement appropriate for bonding digital ground to chassis ground?
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Should the TVS diodes return to Chassis_GND or PCB GND in this design?
TVS Diode Return Path
All I/O lines (Hall, FW, RV, RGB, etc.) use unidirectional TVS diodes referenced to Chassis_GND.Is it correct to route TVS return to chassis ground instead of PCB GND?
12 V & 5 V Output Protection
For the auxiliary 12 V and 5 V rails, I used Polyfuse (resettable fuse), Series ferrite bead, TVS diode to chassis ground
- Is the placement of the TVS after the polyfuse and bead correct?
- Should the TVS diode be referenced to chassis ground or PCB ground?
1 answer
You need to be clear about what problem you are trying to solve.
for clipping incoming signals to safe levels, use the ground as close as reasonably possible to whatever is receiving the signals. That would probably be your circuit board ground in this case.
If you are trying to reduce radiated emissions from your box, the reference ground should be the chassis as close as possible to where the cable enters the conductive chassis.
In some cases you may want both. For example, if you have signals inside a shielded cable, then make the hole in the chassis as small as possible and tie the shield to that chassis as close to the hole as possible. In this case, you do NOT want to bring the cable all the way to the PCB inside the box and terminate the shield there, even if the PCB ground is ultimately tied to the chassis. At high frequencies, a roundabout path is not the same as a direct and short path.
In the example of the shielded cable, the signal wires then proceed past the chassis to the PCB. Then you clamp the signals there against the PCB ground.
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