power consumption after shutdown

Richard A. Smith richard at laptop.org
Mon Feb 16 14:41:25 EST 2009

Richard A. Smith wrote:

> The instrumented setup only has a current measurement resolution down to 
> about 1mA.  So there's room for a lot of error in that measurement. 
> Looking at the schematics I see that there are quite a few other parts 
> that share the 3.3V rail with the EC so 1mA or so seems reasonable.
> I've started a long term measurement test using the ACR guage inside the 
> battery.  I'll check it on Monday.

Based on a long term (44 hour) test I've measured that the average draw 
of the XO when powered off is 1.64 mA.

Although this seems to match my previous measurement it actually does 
not.  This is a measurement of the battery voltage rail.  So 1.64 mA * 
6.68V = 11mW.  I was expecting a number half of that.

The previous measurement was on the suspend 3.3V rail which would be 
5.3mW so there's 5.7mW unaccounted for.  Some of this is probably the 
switching regulator since I doubt its very efficient in this range.

In any case Leaving the battery in the XO will cost you about 1.3%/day.

Richard Smith  <richard at laptop.org>
One Laptop Per Child

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