AN2680 datasheet(10/15 Pages) STMICROELECTRONICS

10 / 15 page

Software flow

AN2680

10/15

0 to 100% as the measured temperature increases from Tos to Tmax. Tmax is the value of the

temperature set through the firmware at which the fan runs at maximum speed.

Thus to control the duty cycle of the PWM signal a linear relationship is established between

the measured temperature and the duty cycle of PWM. As the measured temperature ramps

up, the duty cycle is also moved towards 100%.

The linear relationship with temperature is controlled by the following conditions:

●

Temperature < threshold value; duty cycle is made 0% and thus fan is OFF.

●

Threshold value <Temperature < Tmax value; duty cycle is ramped linearly towards

100%, thus fan runs at variable speed.

●

Temperature> Tmax value; duty cycle is made 100%, thus fan runs at maximum speed.

The duty cycle is handled by writing in the registers of the PWM peripheral of the

microcontroller.

Figure 5.

Software flow diagram for alarm control

Power up the system

Initialize the I

communication

Configure the Temperature

Sensor Device

Alarm LED

Measure the temperature

(T)

Measure the temperature

(T)

Alarm LED

OFF

YES

Is Alarm

LED ON?

YES

T >= Tos?

T <= Thys?

AN2680 Datasheet(PDF) 10 Page - STMicroelectronics