Wow, ok that is low. Then I'm really close to the limit, with 15mA for LEDs + 10mA CPU.
Interesting what you said about the GPIOs - luckily I do not do any really noisy stuff like PWM on LEDs or like (so switching signals will be only a few microamps). Looking at my design the only GPIOs connected to an external connector directly are the USB DP/DM pins, but I cannot really avoid that without using a separate MCU for USB communication.
I don't mean like PWM and stuff, I mean it could be noise from the CPU core itself too -- anything that draws varying power within the chip.
Now, internal stuff could be down in the microvolts -- could? should? hopefully is? I suppose with a bad enough design it could be in the mV. But yeh, who knows, they never document stuff like that.
Mind, same is true for any other chip too, just that most have multiple power pins, dividing the ground-return impedance by a significant factor (4, 8, etc., i.e. -12, -18, ... dB).
USB is shielded so that's fine. Well, maybe less fine if you're doing USB HID (usually unshielded?), maybe prepare for some optional filtering components if that's the case.
But current rating of "every other pin" is there because of the Rds_on of the output stage transistors.
No such thing with Vdd / GND, at all. Actual current rating is defined, as commented by many, by bond wires and how they exactly connect to the metal layers (power rails) in silicon. Without specifications, one can't know, but assuming it isn't any better than the weak 50-ohm-ish MOSFETs is quite pessimistic IMHO.
Not just Rds(on), also electromigration and stuff there too.
Pessimistic? Sure. I've seen devices rated for supply currents from 10mA to 200mA or more per pin (or probably much more when it comes to big CPUs' Vcore, but that's BGAs). So then do you know which class of design they used, is it the 10mA or the 200mA kind?
Or like, if they don't say what the ESD rating is... what default should you assume, if any at all? Supposedly, 1kV HBM is the traditional minimum. But if they don't even say what standards they're meeting, let alone what type and level... then what?
Tim