High power consumption in StandBy mode

[tuomas]

Posted on March 21, 2012 at 16:53

Hi

I have my F205 (and F405) going to StandBy mode and waking up properly. I have confirmed that from the PWR_CSR register's SBF flag and also the 25MHz HSE is turned off properly according to an oscilloscope (I don't have LSE). But I'm getting quite high power consumption and I have no idea why. Here's a blog post with an image of the board to get some idea about the stuff in it:

http://snowcap.fi/blog/2012/01/24/control-board-pcbs-arrived/

The board takes around 24mA when running (power led on and an user led blinking). In StandBy mode it takes about 5.5mA with the power led on. According to my measurements and tests the leds take a bit over 1mA each. This is measured by bypassing the 3.3V regulator and providing 3.3V directly. Here's the code I'm using to go to the StandBy mode:

1.
SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;
2.
PWR->CR |= (PWR_CR_PDDS | PWR_CR_LPDS | PWR_CR_CSBF | PWR_CR_CWUF);
3.
RTC->ISR &= ~(RTC_ISR_ALRBF | RTC_ISR_ALRAF | RTC_ISR_WUTF | RTC_ISR_TAMP1F | RTC_ISR_TSOVF | RTC_ISR_TSF);
4.
5.
sc_led_on();
6.
__WFI();

Any suggestions about lowering the power consumptions? Thanks.

[tuomas]

Posted on March 22, 2012 at 18:53

My main concern here is if I've done everything I should to properly go to the StandBy mode.

I would appreciate if somebody knows if the code in the previous post should be enough or if I'm expected to do some pinmuxing or shutting peripherals explicitly down.

Thanks.

[alok472]

Posted on March 23, 2012 at 08:57

My suggestion is to refer to the standard peripheral library example for the Low Power Modes. You can run the example on yr board to check the consumption

[tuomas]

Posted on March 24, 2012 at 08:44

Thanks for the suggestion. I actually tried those quickly but couldn't get them to run on my board.

But it looks like it is a problem in our board after all. Although it doesn't have much extra, we soldered a board with the bare minimum and that one takes something in the uA range. So now we need to review the schemas again.

Thanks.

[simonlee0311]

Posted on March 24, 2012 at 11:32

Do you stop the crystal? 

Normally, I will suggest you checking your HW first.

All of GPIO should be at stable state without any floating.

As your measure result, I think the current is caused by crystal, maybe.

[Tesla DeLorean]

Posted on March 24, 2012 at 16:16

Do you stop the crystal?  Normally, I will suggest you checking your HW first.

 

All of GPIO should be at stable state without any floating.

 

As your measure result, I think the current is caused by crystal, maybe.

I believe the OP clearly stated he turned the HSE off, and frankly I think the internal RC's suck more current anyway, which is why the LSI doesn't maintain the RTC from VBAT.

The biggest current draws are likely to come from the GPIOs, and the state of things they are attached too.