STM32F Standby PowerManagement

[michael239955_st]

Posted on February 09, 2014 at 16:40

Hi,

in my project a 2.8V voltage regulator is connected to the VDD pins of the STM32Fxx device. VBat is directly connected to a 3V battery.

After reset the mcu processes some tasks and after that the controller falls into a ''deep sleep'' (Standby Mode). But before i want to disable the 2.8V voltage regulator by the PC13 pin.

How can i reactivate the regulator when the mcu wakes up from the standby mode (by RTC alarm after some seconds)?

What happend when the mcu wakes up and there is no VDD power supply available because the voltage regulator is still disabled?

Greetz.

[chen]

Posted on February 10, 2014 at 10:47

Hi

You need to read BOTH the reference manual and the data sheet for the specific device that you are using.

''Standby Mode'' is the lowest power saving mode and what can wake it depends on the variant. (see the ref and data sheets!)

Are you talking about the internal regulator?

I think everything you are asking is in the reference manual and datasheet. In the reference manual - try section ''Power Controller (PWR)''.

Bear in mind that when coming out of 'Standby Mode' the processor will be reset (Thanks to clive1 for clarifying this!). There is a register which can determine what caused the reset, see the  ''Power Controller (PWR)'' section

[michael239955_st]

Posted on February 10, 2014 at 11:19

Hi,

sorry that was not my question.

I know the functionalty of the standby mode and the wake up sources.

There are three special pins (PC13, PC14, PC15). This pins are activ in standby mode.

I want to put the external 3.3V LDO (supply for VDD /AVDD) into a power down mode.

Therefore PC13 is connected to the EN pin of ther external LDO.

Before entering the MCU standby mode, PC13 pin is set to low and the LDO is disabled.

Now my question:

What happend when the mcu wakes up from the standby mode followed by a reset, but the external LDO is still disabled, because PC13 is still low...so there is no power supply for VDD/AVDD until PC13 is set high.

[chen]

Posted on February 10, 2014 at 11:55

Hi

'' Before entering the MCU standby mode, PC13 pin is set to low and the LDO is disabled.''

Does PC13 stay low when in Standby mode? I was under the impression that the processor is in reset state when in Standby mode and therefore all the IO pins go to their default state (I could be wrong though).

''What happend when the mcu wakes up from the standby mode followed by a reset, but the external LDO is still disabled, because PC13 is still low...so there is no power supply for VDD/AVDD until PC13 is set high.''

Well with no power - the processor cannot work.

You will have to re-design the circuit so that the wake signal to the processor also latches the external regulator ON as well.

[trevor23]

Posted on February 10, 2014 at 12:09

Basically the battery needs to supply VDD when the regulator is off (or not powered). What exact processor are you using? There will be development board for this processor that will have this powering arrangement so look to those for examples.

[michael239955_st]

Posted on February 10, 2014 at 14:09

I want to use the STM32F051x.

The 32F051 Discovery Board is useless, there is no power management.

''The VBATpin powers the RTC unit, the LSE oscillator and the PC13 to PC15 IOs, allowing the RTC to operate even when the main power supply is turned off.''

''When the RTC domain is supplied by VBAT(analog switch connected to VBAT because VDD is not present), the following functions are available:

• PC13, PC14 and PC15 can be controlled only by RTC or LSE''

That means this pins are enabled in standby mode.

So i can use a pullup resistor to the EN pin of the external LDO.

Before entering standby mode, PC13 pulls down the EN pin, the LDO is off.

The state of PC13 is stable (low) until exiting standby mode.

''After waking up from Standby mode, program execution restarts in the same way as after a Reset (boot pin sampling, option bytes loading, reset vector is fetched, etc.)''

So the PC13 pin is in HighZ mode and the external LDO is enable?

I'am right?

Would that work??

[trevor23]

Posted on February 10, 2014 at 14:37

D

oes PC13 have an external pull up or pull down resistor?

PS: mentioning it was a F05xx device in the beginning might have got us here quicker.

[Tesla DeLorean]

Posted on February 10, 2014 at 17:51

A weak pull-up would appear to be where to start.

What's the current draw when the internal regulators are off?