When ESD protection is done between connector and magnetic transformer, I think the bidirectional diode is best suited since the signals are bipolar.
Why unidirectional diodes are applied in reference designs?
Ethernet ESD protection between connector and magnetic transformer, bidirectional or unidirectional?
\$\begingroup\$
\$\endgroup\$
2
-
1\$\begingroup\$ We don't know what reference designs you are looking at so we can't answer why reference designs use unidirectional diodes in your opinion. It seems the topic and body are two different questions. \$\endgroup\$– JustmeCommented Dec 9 at 7:37
-
\$\begingroup\$ ti.com/lit/pdf/tidrap1 \$\endgroup\$– RasoolCommented Dec 9 at 18:10
Add a comment
|
1 Answer
\$\begingroup\$
\$\endgroup\$
The TI design has an error anyway, so the part being unidirectional or bidirectional is irrelevant in that example.
As Ethernet is a transformer coupled isolated interface, the connector side of magnetics must never have ESD diodes that clamp to chassis (or any other) ground potential. And in your example by TI they have just done that. It will not pass the tests, as it should withstand 1500 VRMS or 2250 VDC between Ethernet interface and e.g. metal chassis.
Indeed, if you are going to put ESD protection to the connector side of magnetics, there must only be one protection device across one pair, each pair being protected individually.
It must also allow having both polarities over it, so a bidirectional device with equal threshold in both directions makes sense, but also the asymmetry of unidirectional device may not matter much if the threshold voltage is above Ethernet voltage levels.
