Consumption considerations

AN2687

14/22

Doc ID 14296 Rev 1

4

Consumption considerations

The number of code lines the MCU has to execute to drive the LCD is the same whatever

the CPU frequency. It is then easy to understand that the faster the CPU clock, the faster

these code lines are executed, the less they represent in terms of CPU load, and the less

the MCU consumes.

In order to reduce consumption with both methods, the PCKEN (peripheral clock gating)

also be decreased, especially in the first method (as the contrast can be compensated for by

software) to further reduce the consumption.

The consumption values obtained with the first method (at 3.3 V) are given in Table 2.

Note:

These typical values are given for guidance only. The LCD driver consumption is obtained

by subtracting the consumption of the MCU executing the LCD driver function and the

consumption of the MCU executing an empty loop (with all I/Os configured as output low

level).

The consumption values obtained with the second method (at 3.3 V) are given in Table 3.

Note:

These typical values are given for guidance only. The LCD driver consumption is obtained

by subtracting the consumption of the MCU executing the LCD driver function and the

consumption of the MCU executing an empty loop (with the MCU in AWU mode with all its

I/Os configured as output low level).

Table 2.

First method - consumption (Timer 2)

Clock master

Consumption of the MCU

executing LCD driver (mA)

Consumption of the

LCD driver (mA)

Consumption of the MCU

executing an empty loop

HSI

2.38

0.3

2.08

HSI/2

1.73

0.38

1.35

HSI/4

1.45

0.49

0.96

HSI/8

1.3

0.7

0.6

LSI

1.17

0.94

0.23

Table 3.

Second method - consumption (AWU)

Clock master

Consumption of the MCU

executing LCD driver (mA)

Consumption of the

LCD driver (mA)

Consumption of the MCU

executing an empty loop

HSI

1.08

0.36

0.72

HSI/2

1.12

0.4

0.72

HSI/4

1.26

0.51

0.75

HSI/8

1.34

0.58

0.76

LSI

1.02

0.33

0.69