AnsweredAssumed Answered

TJA1100 MDI interface failing

Question asked by Luke Morton on Nov 1, 2017



I am using the TJA1100 PHY in a hardware configuration as described in v0.2 of the AH1310 application hint, that is:


Connector -> 100nF series capacitor -> common mode choke -> TRX_P and TRX_M pins of TJA1100, with series termination and a TVS diode on the connector side of the capacitor.


With this arrangement, the device usually works fine, but I have been finding some cases where the TRX_P and/or TRX_M lines have shorted to ground, and the device no longer works correctly.


I notice that later versions of the AH1310 application hint suggest different hardware arrangements between the connector and the TJA1100, for example adding ESD protection on the TJA1100 side, and adding a low pass filter between the common mode choke and the TJA1100. Is all this needed, or could it relate to the issue I'm seeing?


It's worth noting that I have been unable to duplicate the problem by deliberately exposing the circuit to an ESD event, or by hot-plugging the connector.


All of the failures I have seen up to this point are with boards that have been known to work in the past, and suddenly stopped working (many, possibly all, while in use).