simpliest 1Mode 7135 "driver"

Hey Guys!

What is the simpliest circuit to use AMC7135 to drive LED?

this?

a switch between somewhere and it runs??

afaik:
*7135 just limits the current
*the Led takes “it Vf” according to the Amps
*the 7135 has to “burn” the Volts that are the difference to the Cells

Yep.

Can you put the switch between V+ and VDD, possibly with a resistor to GRD? Or would that allow parasitic drain?

There is parasitic drain if you switch Vdd but leave the cell in the circuit. How much depends on the individual 7135 as they are inconsistent in this.