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I designed in a Everspin MRAM. Had to take it back out when we learned that the small magnet, to activate a reed switch, near the MRAM would destroy it. It di

I designed in a Everspin MRAM. Had to take it back out when we learned that the small magnet, to activate a reed switch, near the MRAM would destroy it. It did not just lose a few bits, the device was forever dead. We are talking Refrigerator Magnet level field in close proximity. Great technology as long as no magnetic fields are close to the device.

Brian_K_White 2y ago
Ok in looking into this for https://github.com/bkw777/WP-2_IC-Card?tab=readme-ov-file#m-ram-512k-card https://github.com/bkw777/WP-2_IC-Card?tab=readme-ov-file#m-... Everspin claims to be internally shielded for between 25 to 125 gauss depending on the temperature rating and package type (pdf included above). In my case using the parallel interface and TSOP-II package, the Industrial version is the best and is supposed to resist up to 125 gauss. And a fridge magnet is around 100 gauss (obviously they vary widely but I found a random chart that placed fridge magnet at 100). Also magnetic fields drop off with an inverse-cube law so even a small distance drastically weakens the field. So in many applications with a chip inside of some product like a vintage computer, the chip is likely to be at least an inch away from any exterior surface, and often a magnet or coil will also be inside of some other enclosure like a speaker, adding yet more inches of distance. So even the commercial version at only 25 gauss shielding is probably fine in most cases. In my application above it's a thin card with essentially no distance from the exterior to the chip, so any bare exposed magnets like a fridge magnet, or the pretty strong magnet in the base of a flash light right on my desk here, can easily come to within 1mm from the chip. If the shielding claims are true then at 125 gauss the card should be ok even with a mild magnet laying right on the card. Setting on top of something like a speaker should be fine since the speaker magnet is suspended in the center of a box. But I still have to generally avoid magnets or electromagnets. Maybe it can stand up to my fridge magnets, but that flashlight is quite a bit stronger. If you are designing a pcb and can make changes and have room, a common steel rf shield should help a lot as long as it's made of mostly iron or nickel. mu-metal is best but a common plain steel shield should be almost as good since steel is mostly iron. They do sell them in generic form not just custom made: https://www.digikey.com/short/zm42wjmc https://www.digikey.com/short/zm42wjmc
kjs3 2y ago
I did not know that. That's a showstopper for...a lot of use cases. Thanks for the warning.
Brian_K_White 2y ago
Wow that is a biggie, than you. And they are expensive. I have an external memory card for a vintage portable word processor that the full bom ends up about $100 for 512k to build one, and something like over $30 of that is just the mram.

Brian_K_White 2y ago

Ok in looking into this for https://github.com/bkw777/WP-2_IC-Card?tab=readme-ov-file#m-ram-512k-card https://github.com/bkw777/WP-2_IC-Card?tab=readme-ov-file#m-... Everspin claims to be internally shielded for between 25 to 125 gauss depending on the temperature rating and package type (pdf included above). In my case using the parallel interface and TSOP-II package, the Industrial version is the best and is supposed to resist up to 125 gauss. And a fridge magnet is around 100 gauss (obviously they vary widely but I found a random chart that placed fridge magnet at 100). Also magnetic fields drop off with an inverse-cube law so even a small distance drastically weakens the field. So in many applications with a chip inside of some product like a vintage computer, the chip is likely to be at least an inch away from any exterior surface, and often a magnet or coil will also be inside of some other enclosure like a speaker, adding yet more inches of distance. So even the commercial version at only 25 gauss shielding is probably fine in most cases. In my application above it's a thin card with essentially no distance from the exterior to the chip, so any bare exposed magnets like a fridge magnet, or the pretty strong magnet in the base of a flash light right on my desk here, can easily come to within 1mm from the chip. If the shielding claims are true then at 125 gauss the card should be ok even with a mild magnet laying right on the card. Setting on top of something like a speaker should be fine since the speaker magnet is suspended in the center of a box. But I still have to generally avoid magnets or electromagnets. Maybe it can stand up to my fridge magnets, but that flashlight is quite a bit stronger. If you are designing a pcb and can make changes and have room, a common steel rf shield should help a lot as long as it's made of mostly iron or nickel. mu-metal is best but a common plain steel shield should be almost as good since steel is mostly iron. They do sell them in generic form not just custom made: https://www.digikey.com/short/zm42wjmc https://www.digikey.com/short/zm42wjmc

kjs3 2y ago

I did not know that. That's a showstopper for...a lot of use cases. Thanks for the warning.

Brian_K_White 2y ago

Wow that is a biggie, than you. And they are expensive. I have an external memory card for a vintage portable word processor that the full bom ends up about $100 for 512k to build one, and something like over $30 of that is just the mram.