I put the TVS on the other of the 10R (or polyfuse), to lessen the currents it experiences. Contrary to TI's circuit with SMBJ43CA TVS, at ~500pF.
There's a reason they put the TVS at the line side, not at the transceiver side of the resistors: that's because if you do it your way, the TVS appears in parallel to the internal protection diodes of the IC.
Who knows how the current will share between them? (hint: external TVS have higher voltage drop than built-in ESD diodes...) The 10R resistors make sure the most of the energy gets dissipated in the TVS, not the IC.
Reminder that RS-485 devices do not have ESD clamp diodes. They have a wide line voltage range: -8 to +12V or thereabouts. The question is, which diode pulls in first: the internal ESD zener, or the external one?
The internal one will most likely* have a comparable V(I) curve to any other TVS, so it's not so bad putting another in parallel as long as it's lower -- or separated by the resistor, which indeed is to isolate the current somewhat.
*Unless it's a snapback device, not uncommon in ICs as far as I know, but hard to find isolated in the wild;
one of the few examples. Anyone know if transceivers use these internally, or how to tell?
For transient protection, personally, I just toss on a SMAJ6.0CA from ground to each line. Or a higher voltage (9 or 12 say) if more range is required (e.g. industrial EMC spec -- combined with using a wider-range transceiver like the ones mentioned above, to tolerate the higher Vpk).
Bidirectional is better than a unidirectional device, because under normal conditions, we can expect the signal to bounce negative, even with common grounds, and such a condition will cause bit errors.
(I didn't discuss this earlier as the subject was sustained overvoltage.)
I'm a bit "ehh" about protecting a TVS with a PPTC -- even the small chips let through a
lot of energy, and even as robust as TVSs are, they can only take so much (10s, maybe 100s mJ for an SMA size part). And at the ratings needed here (~100mA fuse rating, >=32V maximum allowed drop), you need a fair size (read, slow) chip, offhand I think 1206 or so?
Another excellent use case for hybrid TVS-PPTCs -- these heat up the PTC with a TVS, giving actually reliable protection. They're hard to find stocked, though.
Tim