Part # Application Notes Communications And Networking Computer Power Supply Data Storage Devices Factory Automation Instrumentation Me datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: Fan speed controller based on STDS75 or STLM75 digital temperature sensor and ST72651AR6 MCU


Part Details:

AN2680 Application note Fan speed controller based on STDS75 or STLM75 digital temperature sensor and ST72651AR6 MCU Introduction This application note describes the method of defining the system for regulating the speed of the 5 Vdc fan using an ST72651AR6 microcontroller and digital temperature sensor STDS75 or STLM75. The sensor measures the temperature data and communicates this data to the microcontroller. Based on this temperature data, the microcontroller issues a PWM signal with varying duty cycle to the fan for regulating its speed. The key features of the system are: Microcontroller with I2C interface and PWM peripheral to communicate with the sensor and for regulating the fan speed Digital temperature sensor to measure the ambient temperature 5 Vdc fan to show the speed regulation Section 1 highlights the features of the STDS75 or STLM75 sensor and explains its interfacing with the microcontroller. Section 2 explains BLDC fan management and PWM signal control to regulate the fan speed. Section 3 focuses on the hardware setup and in Section 4 the application flow of the system is defined. February 2008 Rev 1 1/15 www.st.com Contents AN2680 Contents 1 Digital temperature sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Theory of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Interfacing of sensor with the microcontroller . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 Configuring the sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.4 Alarm signal behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 BLDC fan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 Principle used for fan speed control using PWM . . . . . . . . . . . . . . . . . . . . 5 2.2 Method of fan speed control using a power MOSFET . . . . . . . . . . . . . . . . 5 2.2.1 PWM control using transistor at low side drive . . . . . . . . . . . . . . . . . . . . 5 3 Hardware setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1 Description of the hardware setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1.1 Sensor - microcontroller connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1.2 Microcontroller - fan connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4 Software flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.1 Description of fan control logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.2 Description of alarm control logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11


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