± usage and absolute sign ambiguity

Question

This is from the Datasheet for Texas Instrument's NE5532:

Does this mean I can safely supply Vcc- = 0V, Vcc+ = 30V, and let all other voltages swing within that range?
If that's the case, then that would be one of the ways I've been reading these datasheets the wrong way. Values would usually show up like this:

I used to think that that meant the absolute maximum potential difference between the supply pins should be 22V.

Why is it expressed as ±22V when they could just say 44V?
Why use the ± symbol at all?
Why say 'absolute' then present a negative value?

Answer 1

You are almost right.

One other very important characteristic is the common-mode range: In conventional opamps this must not get closer to the supply rails that ~2V. For the NE5532 it is shown as below. Note that when supplying +/-15V the device is only guaranteed to work if the inputs are in the range of +/-12V. A typical device will go about a volt further than that to +/-13V.

The device won't be damaged if either input goes to either the positive or negative rail but it won't function as an amplifier. In fact with some devices, the gain may actually reverse and the negative feedback will turn positive causing latchup.

Most opamps of this type have traditionally been used with dual supply rails so the convention is is to describe the supplies as +/-. You could use it as a single supply but the inputs and outputs wouldn't be able to go to ground.

Some amplifiers, commonly referred to as single-supply devices do allow the inputs to go down to ground. Others referred to as rail-to-tail allow signals (input, output or both) to go to either supply and the device still operate. There are often compromises in the operation of such devices though so you need to study the datasheet catefully.

Also be very careful about the distinction between the maximum ratings where the device may suffer damage and the values shown in the characteristics table where the conditions required for normal operation are described

Answer 2

The devices require split supplies for maximum large signal output with 2V lost for headroom to each rail.

This is why the “marketing spec” up top is 32Vpp for +/-18V supply or 36Vpp. However the recommended use is +/-15V perhaps for power dissipation reasons driving a 600 Ohm load. These are the “Engineered specs”. We use these terms because marketing like to stretch the ratings but don’t say the load rating, whereas the “eng specs” do. I say this from speculation and past experience in the industry.

Answer 3

Well part of the problem is you're focusing on the "absolute" part and trying to interpret it in the mathematical sense as "absolute value" without paying enough attention to the fact that it is paired with other words to form "absolute maximum rating".

Trying to apply the mathematical definition of "absolute value" to the phrase "absolute maximum rating" is nonsensical because a discrete maximum value cannot be both positive and negative, and a range is always positive anyways, so the mathematical definition can't apply here. That means the "absolute" in this case is more of the regular English definition. As in "absolutely do not exceed these maximum limits."

It's almost like trying to apply the mathematical definition of "absolute" to the phrase "absolute power corrupts absolutely." Does that mean having negative levels of power corrupts you? It just doesn't make sense.

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The reason they probably don't list it as 0-30V is generally you can't operate right at the rails and most op-amp circuits operate very near GND (due to negative feedback and virtual GND) so listing 30V implies you can operate near GND, in a way.

Single supply opamps (and rail-to-rail) that can operate right to GND (or very near GND) do list their supply voltage as just 5V. Dual supply typically cannot operate close to the rails (just different design priorities) and do not list their voltages this way.