ST4485EB : Requirement for external TVS diodes for this RS485 chip

[Nilav]

Is it required to put external TVS diodes along with the ST4485EB RS485 IC on the A and B lines? I see the datasheet and notice that there is in-built ESD protection as shown in the data sheet snapshot below. 

Please advise. 

 

[Peter BENSCH]

 

The ESD protection mentioned in the data sheet of the ST4485EB refers to touching the RS485 lines and is guaranteed in accordance with the ±15 kV human body model and ±8 kV IEC 1000-4-2 contact discharge model. However, depending on the requirements and environmental conditions of your system, there are additional standards such as IEC 61000-4-4 and IEC 61000-4-5, which require stronger protection, so that TVS diodes make sense.

The ST4485EB tolerates a differential voltage of ±14V on its lines, so that you can use a bidirectional TVS with 14V clamping voltage depending on the specified pulse profile (e.g. 8/20µs). You could use e.g.:

• SMAJ6.5CA (single bi-directional TVS, 1x per A and B line against GND) or
• ITA6V5B1 (TVS array, can protect 2 RS485 pairs)

Hope that helps?

Regards
/Peter

[Nilav]

Thanks @Peter BENSCH this information really clears my doubts. Appreciate your help.