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I am wondering if ADUM1285CRZ is Bidirectional or unidirectional digital isolator. It says it is Bidirectional, but the block diagram says otherwise. enter image description here

Tha datasheet block diagram shows one direction isolators.

As far as i know, when a digital isolator is bidirectional, internally it functions like this:

enter image description here

Image from: https://www.analog.com/en/analog-dialogue/articles/digital-isolation-solutions-to-design-problems.html

So its functional diagram should be similar (aka for each channel, a dual FR transmitter/receiver).

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    \$\begingroup\$ I would say that having one unidirectional channel in both directions across the isolation barrier counts as a bidirectional isolator, even if each individual channel is unidirectional. The claim of bidirectional communication applies to the whole family, not to any one individual IC, so that can be assumed to be talking about the ADuM1281 and ADuM1286, not the -0 and -5 variants. \$\endgroup\$
    – Hearth
    Commented Feb 19, 2021 at 16:30
  • \$\begingroup\$ @Hearth It can't be bidirectional, because if you use it as such, you defeat the isolation. I think "Bidirectional" just does not apply for these two PNs. \$\endgroup\$
    – Eugene Sh.
    Commented Feb 19, 2021 at 16:33
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    \$\begingroup\$ I've rolled back the edit because it erased critical context for why this claims bidirectionality. \$\endgroup\$
    – Hearth
    Commented Feb 19, 2021 at 16:34
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    \$\begingroup\$ Yes, Hearth is right. I thought the different device family had no meaning to be shown on the question, but it turns out it is the answer to the question! \$\endgroup\$ Commented Feb 19, 2021 at 16:36
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    \$\begingroup\$ Overall bidirectional parts are available, but not bidirectional channels. \$\endgroup\$
    – DKNguyen
    Commented Feb 19, 2021 at 16:37

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I would say that having one unidirectional channel in both directions across the isolation barrier counts as a bidirectional isolator, even if each individual channel is unidirectional. The claim of bidirectional communication applies to the whole family, not to any one individual IC, so that can be assumed to be talking about the ADuM1281 and ADuM1286, not the -0 and -5 variants.

Datasheets often try, especially in the headline sections, to make the most appealing claims about the product that they can manage. Just like any marketing material, you should completely ignore this information and go directly to the fine print--or at the very least, you should use the headline information for nothing more than determining if it's worth the trouble of reading the full datasheet.

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  • \$\begingroup\$ "Datasheets often try, especially in the headline sections, to make the most appealing claims about the product that they can manage" Unfortunately, it looks like they do, and create such misconceptions. \$\endgroup\$ Commented Feb 19, 2021 at 16:37
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    \$\begingroup\$ @ChristianidisVasileios It's marketing! Just like any marketing, you should ignore it entirely and read the fine print. \$\endgroup\$
    – Hearth
    Commented Feb 19, 2021 at 16:39
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    \$\begingroup\$ @ChristianidisVasileios This isn't a new thing; all the way back to the dawn of electronics you would see datasheets that talk about how their product is excellent for X use or has really great Y characteristic, and then only later in the fine print would they mention that it's actually terrible for W use and has abysmal Z characteristic. \$\endgroup\$
    – Hearth
    Commented Feb 19, 2021 at 16:55
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    \$\begingroup\$ @ChristianidisVasileios I think it's just common sense to be honest. It's fairly evident the the first time you see a datasheet address a family of parts rather than just one. \$\endgroup\$
    – DKNguyen
    Commented Feb 19, 2021 at 17:09
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    \$\begingroup\$ @Christianidis V -- It is, loosely speaking, "bidirectional" in the context of a situation in which you are trying to isolate a pair of single ended Tx/Rx UART lines, and "data is going both ways". That is a common use of that chip. Per your other question from earlier today, you could very well apply the 1281/1286 on the UART side of the FT232 and get effective isolation from your USB. I feel your frustration about some misleading stuff in datasheets. There are a lot of things they don't teach you in school, some even more annoying. \$\endgroup\$
    – Pete W
    Commented Feb 19, 2021 at 18:07

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