slide 10 - you name your own 'power use profile' terms that are not in step with vendors names?? Seems to add yet another level of confusion ...
RUN -->> ACTIVE??
DEEP SLEEP -->> STANDBY??
Low power is very important for the reasons stated in class 1 as well as environmental and social reasons relating to energy use and lifestyle social determinants. An interesting and perhaps, at first glance, 'fun' application is monitoring or controlling temperature in a refrigerated vehicle I suppose. Perhaps there are bragging rights for keeping Eskimo pies at constant and sub-zero temperatures driving across the desert. Perhaps a better total energy efficiency is to eliminate the application.
Good engineers, being good citizens and wise stewards of the planet's energy sometimes might want to consider recommendations for a broader conservation of energy and resource utilization at the higher system levels.
@John- Shelf life was included on my slide since I just did a screen capture of the Energizer video. They probably include it since it is important to their end customers- probably not as important to us as designers (unless our designs have batteries in them and then sit on the shelf for a long time in inventory. Seems like it would be uncommon however.
@John- The currents in Table on slide 12 are estimates from the data sheet. These can be measured using a number of techniques- ammeter, capacitor to via a shunt resistor and a scope. There are issues with each of these techniques I cover in a previous class so take a look at previous PPTs/audios if you want more details.
On batery capacity that varies with drain rate- you are correct and it can be difficult to use manufacturers data (typically in graph form as you say) but it is possible to do some estimates that 'bound' the lifetime using these graphs. Not as accurate as you might wish, but should be accurate enough for most applications (you should be able to show that you can run for at leasy 2 years- for example- but may not be able to say exactly how much longer than 2 years).
So the avg current can be determined. But to find lifetime you need to know the real battery capacity. Data sheets won't tell you the capacity directly, because a batteries capacity (mAh) varies tremendously with the drain rate. Even if they give a graph it's on a low resolution log-log scale and it's practically impossible to determine the capacity at YOUR load -- especially if your load varies, for example if current varies with battery voltage. How do you know a battery's capacity?
On the topic of 22-year battery life, Jack Ganssle wrote a good article about the (multi-)decade from a coin cell claims from manufacturers. His take was that things like the capacitor leakage (which I see is mentioned in this PPT) and other possible nanoamp leaks (also I would add, like Warren just did, battery life and self-discharge) make multi-decade runtimes on coin cells more or less impossible.
The mcu is only one part, and sometimes a small part, of the power puzzle.
While you are waiting feel free to post any questions you have from previous classes or topics you are most interested in about todays topic- Extending battery lifetime. I will try and address them during todays class.
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