Micropower amp disabling

[Reg]

What is the correct way to disable one (of two) op-amps in a micropower
package and no, I cannot use a single package micropower op-amp?
I need to keep the quiescent as small as practical.
thanks
Reg

 

[Spehro Pefhany]

What is the correct way to disable one (of two) op-amps in a micropower
package and no, I cannot use a single package micropower op-amp?
I need to keep the quiescent as small as practical.
thanks
Reg

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

 

[Eeyore]

What is the correct way to disable one (of two) op-amps in a micropower
package and no, I cannot use a single package micropower op-amp?

Which device ?

I need to keep the quiescent as small as practical.

What do you mean by 'disable' ? You can connect the output to the inverting
input and ground the non-inverting input typically. That'll keep it from
misbehaviour.

It's very unlikely you can turn off the internal currents though if that's what
you were thinking although in the dim distant past I've seen devices that can be
'gated'.

Graham

 

[D from BC]

What is the correct way to disable one (of two) op-amps in a micropower
package and no, I cannot use a single package micropower op-amp?
I need to keep the quiescent as small as practical.
thanks
Reg

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

 

[whit3rd]

What is the correct way to disable one (of two) op-amps in a micropower
package

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.