THVD1520: THVD1520DR Schematic Review

Hi Chinmay,

So a few things:

1. Why do you have a full bridge rectifier on a communication line that is in no way standard to RS-485 and after doing RS-485 applications for years I have never once seen anyone do this - what are you trying to do. 

2. Considering those TVS diodes are connected to the DC outputs of the rectifier I don't know what you are trying to do -  - so what are you trying to do. I can't give you recommendations when those diodes are not doing anything from the RS-485 side - if you are trying to protect the RS-485 bus get rid of the rectifier and just have TVS diodes connected from A to GND and B to GND. Generally speaking the most common TVS diodes for RS-485 are going to be SM712 diodes or something extremely similar but I believe SM712 are usually the cheapest. 

3. Ferrite beads are not required by RS-485 - so if you use them you need to pick them based on applications - generally speaking ferrite beads are the last type of EMI protection we add to an RS-485 bus because they generally aren't that helpful - in ways that a split termination or filtering caps are. So there is no recommended value because we don't typically recommend ferrite beads to be used - and if they are it is going to be extremely application dependent. 

Please let me know what you are trying to do with this application - because at this point I am not sure of the end goal and usually something like RS-485 where it looks pretty much identical in every application - when there are major deviations like this I'd like to understand what you are trying to do because general RS-485 advice may not help you if you are doing something more novel. 

Best,

Parker Dodson