I need to isolate the SPI communication between two chips.
The bottleneck of the communication is on the slave, which apparently can handle up to 2MHz SPI clock frequency.
My idea is to do this isolation using optocouplers. On this first attempt, I used the 4n35. It was just not working, so I looked on the datasheet and I saw the chip takes 10 us to rise and 10 us to lower the signal (on the worst case). This makes its use pointless.
Can someone suggest me an optocoupler that can:
- be fast enought for this purpose (2MHz, but 1MHz is also acceptable)
- be easy to buy and not expensive
I searched over the internet for an optocoupler that met those requirements, but I couldn't find one that was most recommendable.
I'm open to suggestions on how to isolate the communication in a different way, if it's practical.
Best Answer
Borges, there are isolated devices made specifically for digital isolation and even for SPI busses. Texas Instruments and Analog Devices both make these. It's capacitive or magnetic isolation instead of optical isolation. Here is a link to popular device:
ISO7241C @ TI.com
It's also available on digikey:
ISO7241CDW @ Digikey