THVD1420: hot plug-in

Hi Fujiwara,

Yasushi Fujiwara said:

Does it mean this device can be insertion/extraction of RS-485 cable even if equipment are powered on.

It is possible for the device to be plugged into a live bus. But the system needs to be designed properly to ensure the device isn't damaged....

The device itself has it's receivers and drivers disabled with internal references, so it should not see a glitch when plugged in nor should it generate a glitch since it's drivers should be disabled. The system designer should ensure these pins are not enabled immediately after the hot insertion occurs. A simple RC circuit on these enable pins would help prevent turning them on too early during the insertion event.

The PCB traces themselves will have some form of capacitance that will get charged when you plug into though, which could still glitch the RS-485 bus. The point here is the device itself shouldn't case a glitch if designed properly though the PCB parasitic could result in a glitch on the existing powered bus. 

Yasushi Fujiwara said:

At this time, device will not get damage. Is my understanding correct?

You still need to ensure that the device does not see voltages outside of it's absolute max values. If the differential pins exceeded +/-16V, the device itself could still get damaged. 

Additional reading below for hot insertion for differential lines. Please make note about the best practice listed in figure 2 of the document.

https://www.ti.com/lit/an/slla107/slla107.pdf?ts=1708462083622&ref_url=https%253A%252F%252Fwww.google.com%252F

-Bobby