AN1605 Datasheet, PDF(1/7 Page) STMicroelectronics – USING AN ACTIVE RC TO WAKEUP THE ST7LITE0 FROM POWER SAVING MODE

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AN1605 Datasheet, PDF (1/7 Pages) STMicroelectronics – USING AN ACTIVE RC TO WAKEUP THE ST7LITE0 FROM POWER SAVING MODE

AN1605

APPLICATION NOTE

USING AN ACTIVE RC TO WAKEUP THE ST7LITE0 FROM

POWER SAVING MODE

by Microcontroller Division Applications

1 INTRODUCTION

This application note investigates the power consumption during the operation of a typical ap-

plication which puts the MCU (ST7Lite0) in HALT mode and wakes it up at regular intervals by

an external interrupt generated by an active RC circuit.

It also lists the typical consumption values and the parameters on which this consumption de-

pends. The internal Pull up (Rpu) of an I/O port is used for the active RC to minimise the

number of external components. The value of the Rpu varies with the supply voltage of the

MCU and with temperature. Externally, only one capacitor is used.

The ST7LITE0 clock source is configured by option byte to be internal RC with PLL*8. All

measurements are taken at ambient temperature.

1.1 HARDWARE SOLUTION

Figure 1 shows the Hardware setup used to measure the consumption (IDD) at different power

supply voltages.

Figure 1. Hardware Setup

PA0 EI0

VDD

RPU

CEXT

1.2 POWER CONSUMPTION

The power consumption depends mainly on the time period between each wakeup from HALT

(external interrupt interval). The wakeup time period is controlled by the RC time constant. The

value of the Cext is fixed but the internal pull-up value varies with the MCU power supply

voltage and with temperature.

AN1605/0403

1/7

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