TRS3232E: Schematic Review

Hi Anne,

I reviewed the TRS3232 schematic.  Why are there 1-kOhm series resistances on the RIN lines?  Generally I wouldn't recommend this since it will cause some loss of signal amplitude.  (It will form a divider circuit with the input resistance of the RS-232 receiver, which is typically 5 kOhm.)  Other than that, I didn't have any major concerns.

I did see that there was a note that a TVS was not needed on RIN since it can support higher voltages.  I wanted to point out that TVS diodes are generally intended to clamp transient over-voltages like ESD strikes, though, not to clamp DC voltages.  If you need to protect against higher DC voltages, then you should double-check the TVS capability and if needed implement extra protection.  If you are just protecting against ESD, you might see if there is a transceiver whose internal ESD protection is sufficient.

I also noticed you are using level translators to communicate with a 1.8-V IO.  You might consider using TRS3122E as the transceiver instead of TRS3232.  It can be powered by 1.8 V directly, or it could be powered by 3.3 V and a 1.8-V logic supply can be used.  In either case external level translators would not be needed.  The TRS3122E also integrates level-4 IEC 61000-4-2 ESD protection on the DOUT and RIN lines, so it may eliminate the need for the TVS diode as well.

Also, did you intend to start a new thread with your DS160PR410 question?  If so, you can put it in a new thread by clicking "More" underneath the post and then selecting "Split."

Regards,
Max