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I was working on a solar power supply that will switch to battery backup when solar is insufficient, powering an lpc2103 and a couple sensors. Unfortunately, I haven't been able to find any information on the 2103's power consumption at lower clock speeds, though. The datasheet mentions ~41mA at 70MHz with power enabled on all peripherals via PCONP, but I only need to run around 24MHz tops and don't need to have everything running.

Would anyone be able to offer at least a guess at what kind of power consumption to expect at 24 or 36MHz with say a one timer (to wake the device up intermittently), and maybe I2C enabled?

I was able to find this App Note on 2138 power consumption, but I expect the 2103 is significantly lower, and this is also at the maximum clock speed: http://www.nxp.com/acrobat/applicationnotes/AN10421_1.pdf

Is it reasonable to expect running at 24MHz instead of ~70MHz would consume about 1/2 as much power, for example?
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On Thursday 10 September 2009, kevin_townsend2 wrote:
> I was working on a solar power supply that will switch to battery backup
> when solar is insufficient, powering an lpc2103 and a couple sensors.
> Unfortunately, I haven't been able to find any information on the 2103's
> power consumption at lower clock speeds, though. The datasheet mentions
> ~41mA at 70MHz with power enabled on all peripherals via PCONP, but I only
> need to run around 24MHz tops and don't need to have everything running.
>
> Would anyone be able to offer at least a guess at what kind of power
> consumption to expect at 24 or 36MHz with say a one timer (to wake the
> device up intermittently), and maybe I2C enabled?
>
> I was able to find this App Note on 2138 power consumption, but I expect
> the 2103 is significantly lower, and this is also at the maximum clock
> speed: http://www.nxp.com/acrobat/applicationnotes/AN10421_1.pdf
>
> Is it reasonable to expect running at 24MHz instead of ~70MHz would consume
> about 1/2 as much power, for example?

More or less. Power consumption scales linearly with clock speeds except at
the extremes. P is a function of rise/ fall time (and gate capacitances, bulk
resistances, external loads etc), hence the number of these transitions will
be greater with an increasing clock f. However the bulk resistance + external
load stays constant and P will have this constant term. So dropping to say
7Mhz will not drop P to 1/10.
Also wether the controller actually works at a substantial lower clock depends
entirely on the internal architecture.

--
Rgds
JTD
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______________________________
Stellaris® MCU Family: New Parts, New Package, New Price.


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--- In l...@yahoogroups.com, jtd wrote:
>
> On Thursday 10 September 2009, kevin_townsend2 wrote:
> > I was working on a solar power supply that will switch to battery backup
> > when solar is insufficient, powering an lpc2103 and a couple sensors.
> > Unfortunately, I haven't been able to find any information on the 2103's
> > power consumption at lower clock speeds, though. The datasheet mentions
> > ~41mA at 70MHz with power enabled on all peripherals via PCONP, but I only
> > need to run around 24MHz tops and don't need to have everything running.
> >
> > Would anyone be able to offer at least a guess at what kind of power
> > consumption to expect at 24 or 36MHz with say a one timer (to wake the
> > device up intermittently), and maybe I2C enabled?
> >
> > I was able to find this App Note on 2138 power consumption, but I expect
> > the 2103 is significantly lower, and this is also at the maximum clock
> > speed: http://www.nxp.com/acrobat/applicationnotes/AN10421_1.pdf
> >
> > Is it reasonable to expect running at 24MHz instead of ~70MHz would consume
> > about 1/2 as much power, for example?
>

You can achieve very low power consumption if you place the LPC2103 in power down, use the RTC timer to wake it up every second or very minute. For I2C, you might connect the I2C clock to one EINTx interrupt pin to wake up the LPC on I2C input ( you might loose the first data )

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> You can achieve very low power consumption if you place the LPC2103 in power down, use the RTC timer to wake it up every second or very minute. For I2C, you might connect the I2C clock to one EINTx interrupt pin to wake up the LPC on I2C input ( you might loose the first data )

Thanks for the tip. That's basically what I was planning on doing ... I only need to wake up every 15 minutes or so to check all the sensors, log the results, fire them off to the router, and go back to sleep. With something like a 60:1 duty cycle (active maybe 1 minute per hour tops) I'm sure I'll consume hardly any power. But for something like the 'router' devices that need to be on 24/7 it's another matter, and I'm having a hard time figuring out what kind of power consumption to expect in that situation (and I don't have a meter I trust enough to make small measurements like that).

Someone suggested to me something in the order of 10-15mA should be normal, which sounds about right to me. At 24MHz I should be a ways away from the 40mA 'typical' value in the datasheer (@70MHz everything enabled). Just wondering if anyone here has any real world experience to confirm that rough number.

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