How to achieve real low power?

pierreandre · ‎2013-11-18

Posted on November 18, 2013 at 14:47

I'm looking to build a small application which wakes up the uC each 500ms to handle some software loops, and then go back in active halt mode with RTC (alarm and wake up function enabled) and LCD running with LSE. The firmware is working, but the measured power consumption is way too high (near 35uA).

I've checked that the clock is only distributed on RTC and LCD and that each module are off. There is no interrupt pending and the halt() seems to be correctly executed. The GPIO are configured with a fixed reference.

The problem I see is that RTC_ISR1->RECALPF is always 1, don't understand why this one never goes to 0, and how to modify the code so this flag works.

How should I go further to discover what is drawing current?

fggnrc2 · ‎2013-11-18

Posted on November 18, 2013 at 17:58

Argail,

I was never concerned with achieving the lowest power consumption.

Notwithstanding this, I've got some hints for you.

Have a look at AN3147 ''
Power management in
STM8L and STM8AL
''
which explains the low power details of STM8L microcontrollers.
If your application is small, you can run it from RAM and switch Flash and EEPROM off.
If your main does nothing, while the interrupt service routines do the ''real'' work, you can set the AL bit in CFG_GCR.

Good luck in your quest for every micro-amp!

EtaPhi

pierreandre · ‎2013-11-19

Posted on November 19, 2013 at 15:36

Oh, great, I've passed though the AL bit functionality, I was sad because the MCU return to main in all case. Thanks' a lot for this advice!

pierreandre · ‎2013-11-21

Posted on November 21, 2013 at 13:11

Sometime you want to dig a very deep hole, hide inside putting you hands on your ears and swing back and forth ..

I've placed an ESD foam foil between the uC and the LCD bound together with an elastic, yes.. early stage prototype;), and this was the foam which induces a lot of current drawn.

I've now a more realistic power consumption but way too high for the application, let's go the the uA hunting quest like Indiana Jones...