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HOW TO MINIMIZE THE ST7 POWER CONSUMPTION

6.2 EXAMPLE 2: APPLICATION WITH PERIODIC WAKE-UP

This example provides a method for measuring the average current consumed by the micro in

different modes while it cycles continuously through “wake-up” and “sleep” periods. The

measurement is done using the following configuration.

6.2.1 Measurement Configuration

- The PF1 port (through which an external interrupt is applied to MCU) is configured as pull up

interrupt.

- The sensitivity of the interrupt is configured as rising edge.

- Then the capacitor is charged and immediately the MCU is put into the corresponding mode

(Wait, Slow-Wait, Halt) by calling a “WFI” or “HALT” instruction and setting some bits.

comes out of low power mode.

- The capacitor is then discharged by setting the PF1 port to Push-Pull Output at low level and

a small delay is then provided to let the capacitor discharge fully before charging it the next

time.

- The MCU is again put into the corresponding low power mode and the same process is re-

peated. The current consumption is measured in continuous interrupted mode.

- In Option Byte, PLL*2 is disabled, CSS is also disabled and LVD is Off.

Figure 2. Hardware Setup

6.2.2 Consumption

The consumption mainly depends on how frequently the MCU wakes up from different low

power modes. The Wake-Up time in turn depends upon the RC time constant. The value of

PF1

mA

ST72324