

Hardware and Firmware Issues in Using Ultra-Low Power MCUs - pietrofmaggi
http://www.ganssle.com/reports/ultra-low-power-design.html

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keenerd
Just wanted to say that everything in this article about the MCU, capacitors
and diodes is spot on. (I don't do work with coin cell batteries, but I do
have experience with using very small rechargeables and very small solar
panels.)

To add to it, don't use zener diodes for over-voltage protection. They are
extremely leaky. And if you need high value MLCC capacitors you are better off
making them yourself from a stack of (more common) 10uF ceramic caps.

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fpgaminer
Articles like these are great. For those working with ultra-low power MCUs,
it's a gold mine of knowledge, data, and wisdom. For everyone else (like me),
it finds value as an inspiration. The article stands as an example of what
good engineering looks like; the kind of attention to detail and depth of
thoughtfulness we should strive to pour into our own projects.

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sp332
Noob question: why doesn't dropping the voltage increase the current?

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VLM
Positive resistance (like a resistor) not negative resistance (like constant
power output active power supply)

One way to look at it is the power in cmos gates is all burned up fighting
capacitance. You can run a cmos ram in sleep mode for years off a watch
battery, but they'll take "serious" power at MHz speeds.

Think of charging a capacitor and watch the voltage across the cap as it
charges. As electrons trickle in (thats the current) the voltage slowly rises.
It'll take longer to charge that cap up to 5 volts than 3.3 volts. (edited to
add, next step in analogy is you could make that cap charge up to 5 volts just
as fast as it charged to 3.3. volts by cranking up the current...) So by
analogy in your cmos gates the higher the voltage you charge a binary one up
to, the larger the current spikes to get to that voltage representing a binary
one.

There are resistive losses, but not much. Those are positive resistances, too.

So everything comes up positive resistance aka "higher voltage = higher
current" not the other way around.

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yuhong
I wonder if it is possible to actually design a battery that has 20-30 years
life.

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keenerd
Sure, here is one that has been going for 175 years:

[http://en.wikipedia.org/wiki/Oxford_Electric_Bell](http://en.wikipedia.org/wiki/Oxford_Electric_Bell)

