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I'm building a RS485 transceiver module and I wanted to isolate the power and data. I am going for a solution wiht a digital isolator (such as TI ISO7721DR) and a power isolator followed by a RS485 transceiver on the isolated side, but everything needs to be really cheap and very small in terms of height because of mechanical constrains.

I have eliminated RS485 transceivers with built-in signal and power isolation (such as Analog ADM2682E) because they are insanely expensive, from $9 to $15 a pop.

I am then looking at solutions like the TI SN6501, but they require transormers that are absolutely massive in terms of height and overall board area.

Is there any solution that would be suitable for that?

Thanks

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    \$\begingroup\$ How small is small and how cheap is cheap? Put some numbers to your requirements; no one wants to play go fish with suggestions. \$\endgroup\$
    – vir
    Commented Jul 1, 2021 at 21:17
  • \$\begingroup\$ Actually putting pricing constraints on an answer would probably make it a shopping question and off topic. If your just asking for a design then go for it. \$\endgroup\$
    – Voltage Spike ♦
    Commented Jul 1, 2021 at 21:39
  • \$\begingroup\$ So what about other isolated RS-485 tranceivers that can even make their own isolated power? A word of warning though, an isolated RS-485 tranceiver will float, and thus in addition to the data wires A and B, it also requires the ISO_GND to be used as bus common reference. \$\endgroup\$
    – Justme
    Commented Jul 1, 2021 at 21:39

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I just built a circuit around this, and I went with the scheme below initially. I ended up using this circuit (which is high profile with the converter).

enter image description here

Almost all COTS (commercial off the shelf) DC DC converters will be high profile or large area because modules and\or magnetics take up area. You could use this for the converter: https://www.analog.com/media/en/technical-documentation/data-sheets/ADuM5010.pdf . If that doesn't work, then you may have a problem, because a search on digikey indicates that this is the lowest cost module at 4$ with a profile like this, and by the time you add in the cost of a transceiver and digital isolator (at least extra 2-3$), there is no way you can become comparable to ADM2651.

I went with the ADM2561, it's expensive from digikey but 6$ from other distributors in qty 10.

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