AM26C31: HTL drivers

Hi Wouter,

So what voltage are you looking at with HTL - I am asking because usually that can surpass the ratings of standard RS-422/RS-485 voltages. Basically do you need above 5V signaling - the AM26C3x family of devices is powered from 5V and the single ended interfaces are 5V pins - the differential output is not as robust on the driver - so it really can't handle a high voltage short - RS-422 only requires the receiver to be more robust - driver doesn't have to be.  If they need higher than 5V signaling my team doesn't have a good part. 

As far as pure RS-422 goes you will not be seeing new "RS-422" devices from us - this is because RS-485 is electrically compatible (it is actually better in every way to be honest) so RS-485 devices will still be made. The AM26C31 is still popular because it is a 4 channel driver only (the 32 is the receiver) and it works really good for what it needs to do- most of the RS-485 devices are single channel which for encoders/motors (where we see this used a lot) the four channels is usually required. 

Really I wouldn't suggest anything other than the AM26C31 - it was redesigned a couple years ago (still compatible with older systems - but there may be some typical behavior changes) in order to continue selling it into the future - i.e. it shouldn't be going away anytime soon. The other quad part is the basically the same as the C31 but it operates at 3.3V - it is the AM26LV31E. 

As for ESD protection - TI doesn't really have a lot of good offers for protection devices on RS-4xx interfaces - they are usually way more expensive than "cheap" diodes and the performance gains are mixed at best.  You need to have a positive clamp probably 5V to a little higher - the abs max is 7V on the bus - the negative clamp needs to clamp the bus above -0.5V during strikes. There is some level of integrated ESD protection - but external would still be needed in most industrial applications. Generally we suggest like an SM712 type diode - but those only work for RS-485. 

So I guess my questions would be the following:

1. What votlages do you need to signal at

2. How many channels do you need - do you need all four? 

3. Is there a specific ESD protection you have in mind - are there concerns with EFT and/or surge as well in system?

A lot of the applications that we do fit into in this space will use the AM26C31 for 5V signaling and the AM26LV31E for 3.3V signaling. I will note that the AM26LV31E does have much better ESD (that is what the "E" really means on the end) - it actually have IEC 61000 4-2 ratings and not just HBM - and they are about 4-5 times higher on the LV. However that only works if you are communicating with the device with a 3.3V micro and the swing will be less. 

Ultimately - depending on application needs it may be better to set you up with RS-485 as it is way more robust and also loosens limitations around protection diodes (i.e. you use SM712 diodes or similar - the 712 diodes are what should be used with RS-485 - TI for whatever reason has decided not to pursue 712 diodes - so anytime you see "can be used for RS-485/RS-422" on our diodes for you need to take that with a huge grain of salt - because it is case by case basis and will not apply to standard transceivers - only more advanced ones - that is why 712 diodes still are standard). That assumes that the voltages match for application - usually I see HTL and think much higher level signaling  but I want to verify with you if this is the case here as well.

Best,

Parker Dodson