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.
Use an OA with "shutdown":
Hello Steve,
If Fred's solution is too expensive you could use a pnp transistor in the supply that has a Schottky plus series resistor connected between base and ground. That'll let go when the voltage drops too low.
However, this cheap trick will make the 1V cutoff a bit "mushy" and will continue to draw a little base current until you are further down the Vbe curve.
Best might be to let the micro monitor the voltage and turn off everything if below 1V. You'll also need a pnp to switch the opamp supply as FETs won't cut it at these low Vgs levels. Well, a pnp is cheaper anyway. Whatever you do make sure that the opamp inputs and outputs are not driven into unhealthy regions when its power is turned off.
Regards, Joerg
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.
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
In article , Fred Bloggs wrote: [...]
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
Hello Tim,
Probably not. You are right, 1V is too low for the usual micro. But Fred's suggestion of powering the opamp through an IO port is a good idea. As long as the code will turn power off to the opamp when the micro detects that the voltage gets too low for its own sake. Kind of like how a laptop goes from standby to hibernate when the battery begins to fade.
Regards, Joerg
Hello Fred,
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
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