AN1014 datasheet(12/25 Pages) STMICROELECTRONICS

12 / 25 page

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HOW TO MINIMIZE THE ST7 POWER CONSUMPTION

The variation of RPU with temperature and VDD is given in the datasheet.

6.2.2.1 Wait Mode

Methodology: A resonator oscillator is used with fosc at 4 / 8 MHz. PLL*2 is disabled. So, fosc2

is fosc/2. All peripherals are in reset configuration except the ports. So, the SMS bit in the

MCCSR is reset to 0. The CP1 and CP0 bits in the MCCSR are also reset to 0 and hence FCPU

is fosc2. IS21 bit of EICR is cleared and IS20 bit of EICR is set to 1. All Ports are in Push-Pull

Output with low level except PF1 (which is used for charging and discharging the capacitor).

Measurements:

Table 8. Consumption IDD (Wait Mode) for Cext = 1 uF at TA = + 25 °C

6.2.2.2 Slow-Wait Mode

Methodology: A resonator oscillator is used with fosc at 4 / 8 MHz. PLL*2 is disabled. So, fosc2

is fosc/2. All peripherals are in reset configuration except the ports and the SMS bit in the

MCCSR is set to 1. The CP1 and CP0 bits in the MCCSR are set accordingly. Hence fCPU is

fosc /4, fosc/8, fosc/16, fosc/32. The IS21 bit in the EICR is cleared and IS20 bit in the EICR is set

to 1. All ports are set as Push-Pull Outputs with low level except PF1 (which is used for

charging and discharging the capacitor).

Measurements:

Table 9. Consumption IDD (Slow-Wait Mode) for Cext = 1 uF at TA = + 25 °C

fOSC(MHz)

fCPU(MHz)

IDD at VDD = 4.5 V

IDD at VDD = 5 V

IDD at VDD = 5.5 V

3.64 mA

4.06 mA

4.63 mA

5.44 mA

6.16 mA

6.91 mA

fOSC(MHz)

fCPU(MHz)

IDD at VDD = 4.5 V

IDD at VDD = 5 V

IDD at VDD = 5.5 V

40.125

1.38 mA

1.55 mA

1.78 mA

4 / 8

0.25

1.68 mA

1.93 mA

2.19 mA

4 / 8

0.5

2.24 mA

2.51 mA

2.88 mA

4 / 8

2.80 mA

3.17 mA

3.53 mA

3.68 mA

4.16 mA

4.68 mA

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