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MCP9700AT-H/LT Datenblatt(PDF) 8 Page - Microchip Technology |
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MCP9700AT-H/LT Datenblatt(HTML) 8 Page - Microchip Technology |
8 / 22 page MCP9700/9700A and MCP9701/9701A DS20001942G-page 8 2005-2016 Microchip Technology Inc. 4.0 APPLICATIONS INFORMATION The Linear Active Thermistor™ IC uses an internal diode to measure temperature. The diode electrical characteristics have a temperature coefficient that provides a change in voltage based on the relative ambient temperature from -40°C to 150°C. The change in voltage is scaled to a temperature coefficient of 10.0 mV/°C (typical) for the MCP9700/9700A and 19.5 mV/°C (typical) for the MCP9701/9701A. The output voltage at 0°C is also scaled to 500 mV (typical) and 400 mV (typical) for the MCP9700/9700A and MCP9701/9701A, respectively. This linear scale is described in the first-order transfer function shown in Equation 4-1 and Figure 2-16. EQUATION 4-1: SENSOR TRANSFER FUNCTION FIGURE 4-1: Typical Application Circuit. 4.1 Improving Accuracy The MCP9700/9700A and MCP9701/9701A accuracy can be improved by performing a system calibration at a specific temperature. For example, calibrating the system at +25°C ambient improves the measurement accuracy to a ±0.5°C (typical) from 0°C to +70°C, as shown in Figure 4-2. Therefore, when measuring relative temperature change, this family of devices measures temperature with higher accuracy. FIGURE 4-2: Relative Accuracy to +25°C vs. Temperature. The change in accuracy from the calibration tempera- ture is due to the output nonlinearity from the first-order equation, as specified in Equation 4-2. The accuracy can be further improved by compensating for the output nonlinearity. For higher accuracy using a sensor compensation technique, refer to Application Note AN1001, “IC Temperature Sensor Accuracy Compensation with a PIC® Microcontroller” (DS00001001). The application note shows that if the device is compensated in addition to room temperature calibration, the sensor accuracy can be improved to ±0.5°C (typical) accuracy over the operating temperature (Figure 4-3). FIGURE 4-3: MCP9700/9700A Calibrated Sensor Accuracy. The compensation technique provides a linear temperature reading. The application note includes compensation firmware so that a look-up table can be generated to compensate for the sensor error. Where: TA = Ambient Temperature VOUT = Sensor Output Voltage V0°C = Sensor Output Voltage at 0°C (see DC Electrical Characteristics table) TC = Temperature Coefficient (see DC Electrical Characteristics table) V OUT T C T A V 0°C + = VDD GND GND ANI VDD GND VOUT MCP9700 PIC® MCU -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 -50 -25 0 25 50 75 100 125 TA (°C) VDD= 3.3V 10 Samples -4.0 -2.0 0.0 2.0 4.0 6.0 -50 -25 0 25 50 75 100 125 Temperature (°C) + s Average - s Spec. Limits 100 Samples |
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Ähnliche Beschreibung - MCP9700AT-H/LT |
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