Micropower amp disabling

There is no single 'correct' way for all op-amps. If the consumption is minimum with the output railed then you'd have to create that condition. Some op-amps have inputs that draw current if the differential voltage is very large (more than a diode drop or so so you'd have to find or create a slight voltage to bias the op-amp. Some bipolar op-amps are okay to leave the inputs open assuming the other half isn't doing anything too demanding. I usually connect them as a voltage follower and hook the non-inverting input to something within the CM voltage range, but that probably maximizes the current drain. Or find a use for it!

Best regards, Spehro Pefhany

Disabled as in Vout = Vss or Vout = Vdd?

Perhaps use a mosfet at an input to bring the op amp output to one of the rails.

D from BC

The best way is to use an amplifier intended for this, like LM346; just program the unused amps for zero current. Second best is to look at the schematic and see how the driver stage is biased (output stage will be minimal current draw because you're not connecting a load, and input stages are usually not current hogs). For LM358, it looks like you'd want the output HIGH (so pull down the (-) input).

There's not much current at stake, actually; the shared bias network (current sources and mirrors) of the multiple op amps will draw current under all conditions, and probably will dominate any terms other than the driven output currents.