Why does LM386 datasheet indicate a recommended operation conditions of +/- 0.4V for Vinput, which is also the abs max rating of that input?

Question

Why does the LM386 datasheet indicate a recommended operation conditions of +/- 0.4V for Vinput, which is also the abs max rating of that input? I thought that absolute maximum ratings should be avoided with a healthy margin (e.g. 20% or so). I notice that Vcc is derated from 15V abs max to 12V recommended operating range.

What is the safe operating range for VI (Analog Input Voltage) for a robust design?

This information is from the TI LM386 data sheet from 2017 found here: https://www.ti.com/lit/ds/symlink/lm386.pdf

Answer 1

The voltage limits suggest that there are effectively back-to-back diodes from each input to ground. One diode is obvious from the internal schematic.

That also suggests that the voltage limit can be exceeded if the current is limited. Probably that limit can be a few mA

In any case, the minimum gain is 20 and the maximum swing is less than 6V so the output will clip before you get to 300mV peak.

Answer 2

We can't know why TI put the same value than in absolute maximum also to the recommended range.

The original National LM386 datasheet only lists the absolute maximum, and there is no recommended range listed at all. Multiple other manufacturers follow this as well.

On the other hand, it is still correct to state that it is recommended to be within absolute maximum range. So as long as you are within +/- 0.4V it is fine and it will work.

On the other hand, it might give a false impression that it is recommended to always use the full range, and that there is no downsides of using the full range.

In practice, the full input range can almost never be used, because the internal gain is at least 20 and the output must be within the limits of supply voltage, as only some LM386 versions accept supply voltage above 16V.

And of course, sound quality can suffer when going too close to the maximum input range, but sound quality may not be the top priority anyway when using LM386.

So for a robust design, you know your supply voltage and chip gain, and so the input voltage must be anyway limited so the output won't clip.