Robert Rolf wrote:
> So they fabricate a current source that gets turned on to enable
> 'weak pullup'.

I don't think so.  Most likely it's just a P channel high side FET
deliberately made small to have a high on resistance.  In that case it looks
more like a resistor than a current source.

The main distinction of "weak" is that its current is intended to be small
enough to be within the normal sink capability of external components
driving the pin.  The pullup is also designed to tolerate the output
externally held low indefinitely, which is something the standard strong
pullup is not rated for.


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