5V to 2.5V coupler / galvanic isolation

Hello people,

I'm designing an ECG circuit with a digital output that is supposed to be hooked up to an FPGA board, but I have a bit of a problem. My circuit operates at 5V, whilst the FPGA only operates at 2.5V and I also want to galvanically isolate the two. I initially thought I might be able to get an optocoupler to do the job, but it seems there are no optocouplers that will operate with a supply of less than 2.7V. One option would to be to use some sort of a voltage converter (probably switched capacitor) from 2.5V to 2.7V, but this just seems awfully complicated. Anyone have any better advice on other components that might do the job?

Oh, yeah I am using an SPI interface, so I'm going to need something that is bi-directional and has three channels..

Hi , you can use the optocouplers at 5V or 3.3V and a 5 v tolerant buffer like 74lcx245 as level shifter to 2.5V. If you can use a 5v power supply from the FPGA side this is simple , if not , use an insulated 5v to 5v converter like AM1/4L-0505S-NZ from AIMTECH or similar.

Hey mdorian, you are my hero, that should do the trick, thank you so much!d