What are “AC characteristics” in a data sheet?

[vmallet]

Ok I feel a bit silly asking this as I must be missing the ultra obvious...

In a datasheet, what does the “AC” stand for in things like “AC characteristics”, “AC read characteristics”, etc? Example: this atmel datasheet page 5, 6: https://www.futurlec.com/Datasheet/Memory/AT29C040.pdf

With Google I can only find things related to ac/dc current but I want to think this is something different here.

(Edit: removed weird url tag)

[AVGresponding]

Normally it would mean Alternating Current.

The link you supplied is blocked, without more information it's difficult to give a definitive answer.

[Siwastaja]

DC characteristics are unchanging, steady state parameters: such as quiescent (no-operation) current consumption, or the recommended supply voltage range.

AC characteristics are anything where voltages/currents change (quickly enough): such as propagation delays for digital circuits, bandwidth for analog circuits, etc.

[rstofer]

It's regrettable that the datasheet emphasizes the AC nomenclature.  True, the signals are alternating but the more typical datasheet won't be written that way although AC may still show up

http://users.ece.utexas.edu/~valvano/Datasheets/MCM6264.pdf

That's just a datasheet I grabbed without spending any time looking for others.

Anyway, AC characteristics are those things that vary with time like the Read Cycle, Write Cycle and so on.

OTOH the datasheet if very clear about what is being discussed; AC Read Characteristics, AC Byte Load Characteristics and so on.  In every case, they are timing specs.

[GerryR]

It's a shame that it is stated that way, instead of "Pulse / Timing Characteristics."  AC really refers to something totally different.

It reminds me of a company (big company!) that started designating Input Modules as sinking or sourcing as to whether they were sinking or sourcing current to the sensor, rather than what was needed to stimulate the input from the sensor.  I believe they are the only company making such modules (for PLC's) that does it that way to this day, but they are a big company....!  Inputs should always be specified by what it takes to stimulate them by the sensor, not as to what they are supplying to the sensor.

It looks like this will go on forever with the "AC" designation, as well.

[vmallet]

Very helpful, thanks for all the replies. So it is indeed the standard AC that's being abused a bit in this context. Good to know

[coppice]

IC data sheets have always used the term AC characteristics when they usually mean dynamic characteristics. Perhaps the earliest op-amps, which used bipolar supplies and had genuine AC characteristics, started the whole thing, and nobody changed to a more appropriate term when single supply devices became dominant.

[Siwastaja]

Note that this practice is not limited to component datasheets.

While the original, and possibly "official" definitions for AC and DC are alternating/direct current, there is a totally different definition, which may be hard to find explicitly.

Implicitly, it's widely used: for example, in signal processing mathematics, terms like "DC component" are widely used, even though it's only about numbers representing pixel brightness, for example, and in a spatial domain for example (not temporal, even!), so has absolutely nothing to do with direct or alternating current, or current at all; and sometimes not even about time.

Yes, I think we should come up with completely new terms and reserve AC and DC to describe power distribution systems, as originally intended, but oh well.