What is the pin? ADC? For what purpose? What is the source impedance and bandwidth? (50Ω I guess given the generator, but beyond that?) What is your input circuit, or your circuit overall?
I was in the hope of getting information on what a pin can withstand.
At least all other STM32s I've looked at, pin characteristics are reasonably well documented in the data section -- give it a look. You will need the IO pin type/class from the pinout section, then cross-reference that with the allowed pin injection currents, voltage ranges, etc. Note that analog inputs (or pins near an analog section) typically stipulate zero injected current, else the analog stuff may read incorrectly -- charge injection into the internal circuitry messes everything up, and maybe it reads wrong by some counts, maybe whole bits in any position (or comparators gain offset, or work slower, or flip state, or the PLL messes up, etc.).
Anything that's rated as -0.3 to VCC+0.3V (or 0.5 or 0.6 are sometimes seen on MCUs), can be assumed to have input clamp diodes to the supplies. 5V-tolerant pins may be absolute (-0.3 to 7V, say), or VCC-relative, suggestive of the type of ESD structure used there (i.e. zener to GND, or zener or diode-strapped FET to VCC, etc.).
If current injection is allowed, and doesn't mess up any nearby peripherals, it is safe to rely on that as a feature -- but be careful that only that much current is used, including transiently, and respect totals across IO banks or whole chip. Mind also that using clamp diodes typically increases Icc, because they're usually actually BJT structures clamping to VCC/GND with the collector to the opposite side, i.e. the pin current is drawn from both rails, not strictly one (as a true diode would do).
A TVS diode doesn't distort signals (TVS diodes are used on all inputs / outputs on any piece of quality equipment). A TVS diode is similar to a zener diode but with better surge handling capacity. Also, never clamp signals to power rails using a diode. You don't want to push power from an unknown source into your power supply.
Well, it certainly does distort some signals. It wouldn't be a TVS otherwise!
I guess you meant as signals that are intended, nominal range, as opposed to unexpected noise or surge; but those are signals in the general sense as well, so it pays to specify.
Nothing wrong with clamping to supply per se, but one must have a complete list of potential hazards you are protecting against. For example, clamping ESD into a supply of more than a few uF is fine, almost regardless of load current; but clamping, say, a telecom surge, or a cross-wired input, is a different matter.
Clamp diode arrays often include a supply TVS as well, which can be biased by the signals themselves (TVS left unconnected), or tied with the supply which also provides clamping to the circuit generally.
Clamp diodes are generally acceptable for analog purposes, but the impedance does matter, as well as bandwidth and linearity. Zener/TVS are less preferable as they have a softer knee and higher capacitance. Very small clamp diodes (<1pF Cj) are available for broadband applications (e.g. USB3, HDMI, etc.), which would also do well on high impedance and high bandwidth analog signals.
Tim
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