Hi Carlo,
Thanks for posting your question on E2E. It is an interesting question.
For the fanout, are you talking about an application like this?
http://www.ti.com/tool/TIDA-01365
The way the fanout is implemented will have it's own set of limits to the maximum number of nodes and data rate. You would need to set the logic in the automatic direction control accordingly.
The reference design I linked to is for a 1:4 fanout that works for 200 kbps with automatic direction control. This is done using the SN65HVD3082 RS-485 transceiver. You could replace these with isolated RS-485 transceivers, such as ISO3082, ISO35, or one of our new devices like ISO1410 or ISO1500.
Each of these devices is an 1/8 unit load, which means you can have up to 256 nodes on a bus. The actual number of nodes will also be limited by the bus length, other components on the bus, and datarate. From the ISO35 Datasheet (page 19):
10.2.2 Detailed Design Procedure
There is an inverse relationship between data rate and cable length, which means the higher the data rate, the shorter the cable length; and conversely, the lower the data rate, the longer the cable length. When connecting a node to the bus, the distance between the transceiver inputs and the cable trunk, known as the stub, should be as short as possible. Stubs present a nonterminated piece of bus line which can introduce reflections as the length of the stub increases. As a general guideline, the electrical length, or round-trip delay, of a stub should be less than one-tenth of the rise time of the driver. The RS-485 standard specifies that a compliant driver must be able to driver 32 unit loads (UL), where 1 unit load represents a load impedance of approximately 12 kΩ. Because these devices consists of 1/8 UL transceivers, connecting up to 256 receivers to the bus is possible.
A 1:4 fanout would be possible with the ISO35 at 200kbps. More work would be needed to determine if you could do a higher fanout with a faster signaling rate.
What configuration of fanout are you trying to design? What is the desired signaling rate? What isolation rating do you need?
Best regards,
Dan
