How to isolated a 3.3V signal

[viktor2113]

Hi,

I'm working on the design of a board with RS-485 with an isolated transceiver, so I need to isolated the supply (3.3V). How can I do it? I couldn't find any component to do it (only the RSZ-3.33.3HP but it's too big for the size of the board I'm working on). I have checked Dc-Dc isolated converters and so.
Any idea?
I checked maxim, ti and many other manufactures and nothing...
Thanks so much,
Victor

 

[Harald Kapp]

I have checked Dc-Dc isolated converters

That's what you need.

You can buy them as modules e.gh. from Recom, Traco and othes, or build it yourself using any of the appropriate DC-DC converter ICs from the manufacturers you named.

I checked maxim, ti and many other manufactures and nothing

Unbelievable. What did you check for? These manufacturers will not sell you the complete converter but the controller ICs to build your own converter. You'll have to look into he data sheets and application notes to find sample circuit designs.

 

[KrisBlueNZ]

I doubt you'll be able to transfer any significant amount of power across the isolation barrier in much less space than the RSZ-3.33.3HP. The size of the transformer is the critical factor, and going to less tightly integrated solution will just make it bigger.

 

[viktor2113]

Hi,
Thanks for the answer.
I found something really interesting.
It's a IC with signal and power isolated. The ADM2582E from Analog Devices.
So I would say my problem has been solved.
Thank's again

 

[KrisBlueNZ]

Wow! Yes, it looks like you've solved your problem! Good work!

That's a neat device. It uses "chip-scale air-core transformers" operating at 180 MHz to transfer signals and power across the isolation barrier. The power isolator can supply 55 mA and the device can drive a fully loaded RS-485 bus. It's packaged in a standard 20-pin wide SOIC. And it's surprisingly cheap! (USD 10~15 from Digikey.)

Thanks for letting us know about this device

 

[viktor2113]

Yes! I was also surprised about the price, let's play with it

 

[KrisBlueNZ]

Yes, please let us know how you get on.

 

[Harald Kapp]

With that chip take care and observe the application notes. These chips tend to generate nasty EMC noise and need careful layout.