THVD2410: Schematic review

Hi Caspar,

1) How long is the bus going to be for COM1? 

There is no termination present on the schematic which is strongly advised for both terminal nodes (start and end nodes). If this isn't a start or end node it does not need to be terminated. However in relatively short busses with slower devices you may be able to get away with not using the termination - so please confirm if you know the distance. 

That being said - it wouldn't be a bad idea to at the very least add a termination resistor pad that can be placed if needed. 

2) It seems to have a discrete pi filter - generally we don't see a lot of this type of filtering because you are adding a series impedance onto the data line which is something we tend to avoid + caps to ground can be problematic - at the very least they do decrease max bus distance as well decrease the maximum number of nodes on the bus. That being said the data-rate system is running at + the values listed for the filtering components the series is minimal, but the 1000pF capacitors are going to load the bus quite significantly and you will see a decrease in max effective bus length (at worst case signal, fundamental frequency, which is an alternating bit stream (010101..) at 115.2kbps)  the capacitor will  have a ~2600 ohm impedance - which is a pretty significant load and could decrease max bus length - but by itself shouldn't cause issues for transceiver) . If this does occur shrinking the 1000pF (C1124,  and C1125) may be necessary. 

 Beyond that I don't see a lot of issues - my main concern is lack of termination, but depending on system setup that may be okay. The 1000pF capacitors on the pi filters will degrade max distance , but once again based on system setup and length this may be okay and not an issue. Adding a termination resistor pad and being aware that you may need to shrink your filter components slightly would help moving forward in case customer finds they need to make these small changes. 

So please let me know on the length of the bus so I can better tell how much you actually need the termination and how problematic those 1000pF caps could be.  

Best,

Parker Dodson

Hi Parker, I think the Termination resistor to be shown in the second picture. (C1102, C1104 and C1106)

Can't you find the second picture in E2E's system? Maybe I'll post it again.

Sorry, R1102, R1104 and R1106.