Power & Ethernet Through the Breakaway

The same pogo boundary has to carry both 48 V ground power and Ethernet, which is kind of an awkward combination. They fail in completely different ways, so I did not treat them like one routing problem.

48 V Path

For the power side, the number I actually care about is the resistance of the entire assembled path:

ground connector → ground PCB → pogo contacts → vehicle PCB → vehicle connector

A trace-width calculation does not know anything about pogo/contact resistance, so I measured the finished interface pin to pin instead.

Umbilical power path schematic — The 48 V path through the breakaway interface.

Measured power transfer

Before

48.0 V

After

47.7 V

0.3 V total drop across the complete assembled umbilical path.

The useful result is the simple one: with the real boards and contacts in the loop, I only lost 0.3 V across the full path.

Ethernet Path

Ethernet wants basically the opposite thing from the power path: not huge copper, but a clean differential transition and a sane return reference.

I kept the pair transition compact, preserved pair assignment through both PCBs, minimized unnecessary stubs, and kept the path referenced as it crossed the connector region.

I checked Ethernet through the fully assembled pogo interface so the test included the real contact geometry, not just two PCBs sitting on the bench.

Umbilical Ethernet and ESTOP schematic — Ethernet and ESTOP/control paths through the same interface.

Umbilical Ethernet routing — Differential-pair routing through the compact breakaway PCB region.

Protection

Because the umbilical is repeatedly handled during integration, the externally exposed power and Ethernet paths include transient/ESD protection close to the interface.

The idea is to eat the ugly cable/handling transient at the interface instead of letting it wander deeper into the avionics stack.