Hi
I again took a buffer (voltage follower) formed of a generic R2R-IO, unity gain-stable CMOS opamp (MIC7300, TLV9001...). Those supply (or sink) 40 mA and more. But the max. output current depends on the output voltage, so, if we want to continue with that approach, I'd likely add a BJT current helper stage behind the opamp (BJT collector on 5V). We have almost no dynamic demands on that opamp, so disregarding any phase errors we introduce by driving large capacitive and resistive loads, it would work w/o a BJT, but let's see...
Heh, I just prototyped something last weekend for another project with controlled VIO using a mcp6001 and a N-mos pass transistor. ( It sure doesn't have the lower drop-out configuration but I think it's more stable that way ).
So I don't see an external ref voltage input on that PCB... maybe your use case would explain your needs here! ;)
I don't see the need for a external vref input. VDDANA is fine.
Cheers,
Sylvain