10F222 Wake on pin change

[ruijc]

With that said I really wouldn't want to run it at anything above 5.5V......

I agree...But for that you can just add a diode in series to lower the voltage down a bit.

Regards
Rui

[AvionicsMaster1]

Good idea on the diode. Thanks.

I know what RTFDS says but for what I'm doing I assume the four AAA batteries are putting out somewhat less than 1.5V and typically the four pack is close to 5.6V. After a short period they are below the 5.5V level and stay like that for a long time with only a 3uA draw. They'll last even longer if I can get it down in the nano Amp range.

I've yet to try the ASM sleep but will try soon. Thanks for ideas.

[Charlie]

Brand new batteries will actually put out more than 1.5V. I'd recommend the diode. Also helps for the day you accidentally put them in backwards. Or use NiCDs.

[Demon]

Would a low drop off 7805 help?

Robert

[Charlie]

How low is low? They usually need over a volt. Can you point to a spec sheet?

[HenrikOlsson]

Hi,
I don't really see the point of linear regulator. A 5V one, LDO or normal, will drop out of regulation pretty quick, then it behaves as if it wasn't there in first place - or worse. Using a lower voltage like 3.3V or 2.5V will only turn useful energy into heat in the regulator so that's no good either.

The "best" way would of course be a switching type boost/buck converter/regulator so that the PIC can be fed 2.5V (or whatever) from "any" supply voltage, the good thing about this is that the PIC Draws much less current at lower supply voltages so provided the converter/regulator is efficient you'd get more use out of the batteries. But, it adds complexity so.....perhaps use 3 cells in series instead of 4.

/Henrik.

[Demon]

How low is low? They usually need over a volt. Can you point to a spec sheet?

I haven't used one yet. I checked a few and can't find one that comes even close to what is needed here.

They should call them NAMDO; Not As Much Drop Off instead of LDO.

Robert

[HenrikOlsson]

Hi,
For reference, the LP2950 has a maximum specified drop out voltage of 450mV @100mA load and 80mV @100uA. But like I said, for this application, I don't think using a linear regulator is a good idea.

The quiescent current of the regulator alone (the LP2950 that is) is 75uA which isn't much but it means that the regulator alone pulls like 50-100 times more current than the PIC does when it's sleeping.

/Henrik.