ISO1450: ISO1450 transmit distance questions

Hi Andy,

Thanks for reaching out. Please see my inputs below,

Andy Liu3 said:

1. What is the maximum communication distance ISO1450 can transmit?

The maximum communication distance that one can achieve on RS-485 bus depends on multiple factors, please do take a look at the below FAQ that provides a relationship between the cable length and datarate. You can take the readings in the plot as an approximation to determine the maximum achievable communication distance for customer datarate.

https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/713416/faq-what-is-the-speed-vs-length-correlation-for-isolated-rs-485/

Andy Liu3 said:

2. How many devices can be mounted on ISO1450 at most

RS-485 standard defines support upto 32 loads which each node defined as a unit load while the devices in the present time support much higher number of nodes. ISO1450 only acts as 1/8th the unit load thereby allowing support for upto 256 nodes. If you have all ISO1450 or similar devices with 1/8th unit load on the bus, you can support upto 256 nodes on the bus.

Andy Liu3 said:

3. Is the matching resistance(between A and B pin) of ISO1450 related to the communication distance, or how does the matching resistance match the distance?

The termination resistance isn't directly related to the distance but is necessary to achieve error free communication over RS-485 bus. Please do checkout the below FAQ for more information on this.

https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/713418/faq-when-do-you-need-termination-on-an-rs-485-bus-and-what-are-the-advantages-and-drawbacks-to-the-system/

You could also share the below two application notes with customer for more information on this topic.

http://www.ti.com/lit/slla070
https://www.ti.com/lit/pdf/slla431

Let me know if you have any further questions, thanks.

Regards,
Koteshwar Rao