Battery consumption for MCU

[ELECTRONIC_BUGGER]

Hi,

I am planning to use Battery CR2032 for MCU application.
I have decided to go with STM32L031x6

I would like to check mAH consumption of MCU to make sure battery is capable (CR2032 Battery Capacity is 220mAH) for certain hours or days.
Can you please help me how to do the calculations.
From controllers-
I am using Internal CLOCK, one SPI protocol, one I2C Protocol and 3 GPI (Interupts) and 1 ADC

I need general power consumption to start for battery?

Regards
Bharat

 

[danadakk]

Does ST have a power estimator tool for its processors ?

 

[KlausST]

Hi,

You say "protocol" .. which in most cases is software. I guess you mean interface.
But none of these interfaces consumes significant power as long as idle
And when active the I2C pull up resisitor draw current ... and in both cases thecommunication partner will draw current.

Regarding MCU: It depends on so many thinks, one can not give yu ayn current consumption "expectation".
A 100% active MCU on 72MHz may draw by a factor of 1000 more than a 1MHz MCU 99% in power down.
Not to mention all periferals.

Usually every MCU manufacturer provides in the datssheets about current consumption under various conditions. Usually they additionally provide documents regarding "low power consumption" techniques.

In mayn cases the periferals draw more current that the MCU.

Klaus

 

[ELECTRONIC_BUGGER]

Hi,
Thanks for your reply.

Still how to calculate avaerage power consumption?

 

[FvM]

As mentioned by KlausST a low power uC application will stay most of the time in power save modus, typically with nA quiescent current. You need to plan intended uC activity and estimate power consumption. That's impossible without knowing application details.

 

[danadakk]

Just a suggestion, contact ST Micro support and ask if there is a power estimator tool and/or
application note on power estimation .....

 

[doraemon]

Hello!

As said above, contact the microcontroller maker might be a good solution. And if you want to save
time, the RTFD method might be useful. Open the pdf, search for power consumption or simply consumption.

I used to design portable measurement devices, mostly with MSP430 (TI's low power chip). The power
consumption is mostly proportiional to the CPU frequency, and in MSP430 case at that time, it was 250 µA/MHz.
Now with a CR2032 (again, data out of my memory) I think the typical discharge was in the range of 1 mA.
This would limit the frequency to 4 MHz for MSP430, supposing there is no other power consuming component.
And that kind of button battery is always the bottleneck for portable applications.

So to reply your question, a rule of thumb for a very low consumption µC is 250 µA/MHz. No idea with ST
although I use it heavily. Maybe 1mA/MHz or more because the one I'm using is a very big beast (H7x, double core).

Dora.

Hi,
Thanks for your reply.

Still how to calculate avaerage power consumption?

 

[ELECTRONIC_BUGGER]

So, i just checked and Controller frequency is 32MHZ, so could it 32mA consumption.
If i reduced frequency, then can i save battery to drain fast?

 

[betwixt]

Current consumption is mostly due to the charging and discharging of the thousands of capacitances inside and outside the MCU. The faster they have to charge, the more current needed to do it so yes, dropping the clock speed will drop the consumption. Beware of other internal timers and modules that might need configuring to off state and current flowing to and from the I/O pins, they all contribute toward the total.

Brian.

 

[FvM]

As mentioned above, long battery life can be only achieved by putting uC in power save (sleep) mode for most of the time and waking it up only for short intervals. Higher operation frequency can be compensted by shorter active time and does therefore not necessarily affect average current consumption. Careful configuration of all peripherals is necessary, as explained by betwixt.

 

[danadakk]

ST Ap note, not your specific CPU but principles apply :

https://eng.auburn.edu/~nelson/courses/elec5260_6260/slides/Chapter3%20Power%20Mgmt.pdf

Regards, Dana.