Op amp brownout circuit

[Steve Morgan]

I am designing an Atmel-based circuit with an associated single supply
op amp. I do not want the op amp Iq to deplete batteries any further
than down to about 1V after the programmed micro brownout.

Note that the batteries are not to be manually switched off.

What is the simplest way of doing this?

Thank you,

Steven

 

[Fred Bloggs]

I am designing an Atmel-based circuit with an associated single supply
op amp. I do not want the op amp Iq to deplete batteries any further
than down to about 1V after the programmed micro brownout.

Note that the batteries are not to be manually switched off.

What is the simplest way of doing this?

Use an OA with "shutdown":
http://cache.national.com/ds/LM/LMV341.pdf

 

[Tim Shoppa]

Best might be to let the micro monitor the voltage
and turn off everything if below 1V.

Do the new Atmel microcontrollers go that low? Last I checked their
brownout stuff kicks in around 1.8V. (That is pretty good compared to
some others... but I'd still love to hear of something at 1V.)

Tim.

 

[Ken Smith]

In article <42195092.1070009@nospam.com>,
Fred Bloggs <nospam@nospam.com> wrote:
[...]

I think an even cheaper trick would be to power the OA through an ATMEL
I/O pin or use a TinyLogic gate to power it.

Yes, IIRC, the ATMEL chip can easily sink enough current to switch the

ground side of the op-amp power connections.


If you don't need much performance from the op-amp, there are some that
draw very little. The have a gain-bandwidth of only several KHz but the
DC characteristics aren't too bad.


--
--
kensmith@rahul.net forging knowledge

 

[Joerg]

Hello Fred,

I think an even cheaper trick would be to power the OA through an
ATMEL I/O pin or use a TinyLogic gate to power it.

That is an excellent way to do it. However, the bypass cap across the
opamp and maybe across other associated circuitry needs to be taken into
account. The current peak caused by charging and discharging it might
exceed abs max limits. Possibly a resistor in series with the I/O can help.

Regards, Joerg

http://www.analogconsultants.com