AN2476 datasheet(25/49 Pages) STMICROELECTRONICS

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AN2476

Power supply and clocks

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1.8.7

Auto-Wake-Up (AWU) from low power mode

The RTC can be used to wake-up the MCU from Low Power Mode without depending on an

external interrupt (Auto-Wake-Up mode). The RTC provides a programmable time base for

waking-up from STOP or STANDBY mode at selectable intervals (using the alarm event).

For this purpose, two alternative RTC clock sources can be selected by programming the

CKRTCSEL[1:0] bits in the MRCC_PWRCTRL register:

●

Low Power 32.768kHz crystal oscillator (OSC32K).

This clock source provides a precise time base with very low power consumption (less

than 1µA added consumption in typical conditions)

●

Internal Low Power RC Oscillator (LPOSC)

This clock source has the advantage of saving the cost of the 32.768kHz crystal. This

internal RC Oscillator is designed to add minimum power consumption (2µA added

consumption in typical conditions).

Table 5.

STANDBY mode functionality

Feature

Functionality in STANDBY mode

RTC enabled

RTC disabled

RTC clock source

LPOSC or OSC32K

None

Voltage Regulators

LPVREG

OSC4M oscillator

Not powered

PLL + Clock Detector (CKD)

Not powered

Flash memory

Not powered

NRSTIN

Yes

External Interrupts

WKP_STDBY pin

RTC Alarm

Yes

Clock Detector

Wake-up latency due to:

MVREG + FLASH + OSC4M

Clock configuration state after wake-up

Reset state

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