Part # Application Notes General Purpose Products ST72325AR9 ST72325J4 ST72325J6 ST72325K4 ST72325K6 ST72325R9 LM135 8-Bit Microcontrol datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: Temperature sensor application using ST LM135


Part Details:

AN2278 Application note Temperature sensor application using ST LM135 Introduction This application note describes how to develop a temperature sensor application using the ST LM135 temperature sensor. Application development was done on a Raisonance REva board. The Raisonance REva board is a universal board with several useful features for application development. It has been designed for quick and easy evaluation of a wide range of microcontrollers. This application uses the ST72325 microcontroller, which is interfaced to REva using a daughter board. The main components required for the development of this application are: ST LM135 temperature sensor ST72325 microcontroller ST24C02 I2C EEPROM ST3232 communication interface Some of the useful features of the REva board are: Digital and analog I/O evaluation features including on-board LEDs, buttons, switches, external analog connector, temperature sensor and potentiometer On-board I2C EEPROM and bus extension connector On-board RS232 driver and DB9 connector SPI, CAN and USB connections (depending on the target device) Embedded RLink for in-circuit debugging and in-circuit programming VDD settings for 1.8 V, 3.3 V, 5 V microcontrollers USB powered, no external power required Section 1 highlights the important features of the LM135 sensor and explains the temperature calculation used in the application. Section 2 explains the temperature sensor management and Section 3 focusses on explaining the application flow. Section 4 gives an overview of the hardware setup required to implement the application. September 2007 Rev 3 1/9 www.st.com Contents AN2278 Contents 1 LM135 temperature sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Temperature sensor application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Software configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4 Hardware configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5 Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2/9 AN2278 LM135 temperature sensor 1 LM135 temperature sensor LM135 is a precision temperature sensor and can be easily calibrated. It operates as a 2-terminal zener and the break-down voltage is directly proportional to the absolute temperature at 10 mV/K. The temperature measurement range of the LM135 is -55 °C to +150 °C. Temperature calculation in Celsius: The ST72325 microcontroller has a 10-bit ADC, so the maximum digital value it is capable of holding is 0x3FF. The maximum voltage available at the V+ terminal of the LM135 (refer to Figure 4) is approximately 4800 mV (after taking into account a voltage drop of 200 mV). Lets say x is the ADC value corresponding to an unknown temperature value. Therefore the temperature value in kelvin is k= [(x * 4800) / (0x3FF)]/10; as zener breakdown voltage for ST LM135 changes by 10 mV for each degree Kelvin change. The temperature value in Celsius is C=(k - 273) / 100. 2


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Application Notes General Purpose Products ST72325AR9 ST72325J4 ST72325J6 ST72325K4 ST72325K6 ST72325R9 LM135 8-Bit Microcontrol.pdf Datasheet