Electronics project notes / EFuse
Confusingly, E-fuses refer to a few distinct things, and some related history.
We can coarsely put them into two or three groups:
Power management/protection
One group is a power protection and management device of some sort, but a somewhat fancier take on it than polyfuses or fuses that burn through once:
E-fuse can refer to ICs that automate limiting current, and/or cutting off current.
Might be "programmable", but often only in the sense that you can change the current it triggers at via external resistors, but nothing more complex than that
There are also fancier protection devices - this is where terms like 'Hot-swap (voltage) controllers' and 'PMIC' also turns up
- things that do overvoltage cutoffs (and undervoltage), short circuit protection, inrush current limiting, and/or reverse polarity protection
- hot-swap voltage controllers are more about a specific purpose: making it safe to plug a board into an already-powered bus.
- PMICs do not just protect, but may also do (some subset of) voltage scaling, source selection, battery charging, brown-out warnings, etc.
https://en.wikipedia.org/wiki/Power_management_integrated_circuit
One-time writing
Another group is about writing once:
There are in-IC traces that are designed to be opened by burning it, once
- e.g. as a means of one-time writing, used for things like storing production-time calibration, or serial numbers
- this is one of a few ways to have one-time programmability
https://en.wikipedia.org/wiki/EFuse
In the context of micro-electronics, antifuse is the same idea,
but the write operation shorts a connection (become conductive) rather than opens it
https://en.wikipedia.org/wiki/Antifuse
Some micro-eletronics even use a combination of the two - and this is one approach to do PROMs, PLDs, and ASICs(verify)
Nearby, useful, yet potentially confusing concept
The above anti-fuse idea probably(verify) comes from doing the opposite of a fuse: shorting something with failure.
Consider that some christmas lights (seemingly more the older, screw-bulb type) would continue working even as single bulbs burned out.
This is because there is something in parallel with each bulb that will will carry the current, where previously it didn't (or mostly didn't -- the details deserve a separate page)
Arguably again: https://en.wikipedia.org/wiki/Antifuse
And then there's e.g. AVR's low-level settings being called fuses[1]
- this seems purely in reference to the one-time configuration
- seemingly meant to be a reference to something low level enough to that affects boot
- confusing because actually, they can be changed many times
- because instead of being one-time traces
- they are actually backed by a small, reserved portion of the internal EEPROM/Flash(verify)