SN65C1168E-SEP: Device response to short circuit conditions at input

Colin Tombari said:

If a device that is sending data to the transceiver shorts, will this cause residual damage to the transceiver?

No, RS485 is quite robust. The standard was defined assuming the pins could be shorted to Vcc/GND/or each other. The receiver network for these device also have an attenuation network that dampens what it actually sees on the CMOS inputs (or BJTs for older devices). So a simple short to Vcc/GND/AtoB will not damage our device both if it's driving or receiving the signal as long as the pins do not exceed the abs max ratings.

Colin Tombari said:

Would a fault like this be able to propagate through the transceiver and affect equipment on the other side?

If both A and B pins were shorted to each other and then to Vcc/GND? or Y-Z then the differential voltage would effectively be 0. So the device would not really be able to see the incoming signal. a differential signal between -200mV and +200mV for this device is undefined. So it may or may not propagate the issue through. 

Colin Tombari said:

Are there any protections in place to mitigate this?

Using a device with an internal fail safe feature would help. Two types of internal fail safe are the ones that push Vth+ below GND (so if a short occurs Va-Vb = 0V but Vth+ is below GND, then R will remain high) and a timer based fail safe that can detect when the voltage sits between 200mV and -200mV and will force Rout high after a set of amount of time between those two voltages.

THVD9491-SEP (I assume you need SEP) has the second one. This one will allow an issue to propagate through but will set Rout back to a logic high after 10ms. The advantage with this set up is the Vth+ and Vth- are more symmetrical and the Vhysteresis is wider than the other type of internal fail safe.

-Bobby