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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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TSC2004 Fiches technique(PDF) 17 Page - Burr-Brown (TI) |
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TSC2004 Fiches technique(HTML) 17 Page - Burr-Brown (TI) |
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17 / 54 page  www.ti.com INTERNAL TEMPERATURE SENSOR Converter AGND SNSVDD +IN - IN DV + kT q @ ln(N) (3) T + q @ DV k @ ln(N) (4) TSC2004 SBAS408A – JUNE 2007 – REVISED AUGUST 2007 OVERVIEW (continued) In some applications, such as battery recharging, an ambient temperature measurement is required. The temperature measurement technique used in the TSC2004 relies on the characteristics of a semiconductor junction operating at a fixed current level. The forward diode voltage (VBE) has a well-defined characteristic versus temperature. The ambient temperature can be predicted in applications by knowing the +25 °C value of the VBE voltage and then monitoring the delta of that voltage as the temperature changes. The TSC2004 offers two modes of temperature measurement. The first mode requires calibration at a known temperature, but only requires a single reading to predict the ambient temperature. The TEMP1 diode, shown in Figure 25, is used during this measurement cycle. This voltage is typically 580mV at +25 °C with a 10μA current. The absolute value of this diode voltage can vary by a few millivolts; the temperature coefficient (TC) of this voltage is very consistent at –2.1mV/ °C. During the final test of the end product, the diode voltage would be stored at a known room temperature, in system memory, for calibration purposes by the user. The result is an equivalent temperature measurement resolution of 0.3 °C/LSB (1LSB = 610μV with V REF = 2.5V). Figure 25. Functional Block Diagram of Temperature Measurement Mode The second mode does not require a test temperature calibration, but uses a two-measurement (differential) method to eliminate the need for absolute temperature calibration and for achieving 2 °C/LSB accuracy. This mode requires a second conversion of the voltage across the TEMP2 diode with a resistance 80 times larger than the TEMP1 diode. The voltage difference between the first (TEMP1) and second (TEMP2) conversion is represented by: Where: N = the resistance ratio = 80. k = Boltzmann's constant = 1.3807 × 10-23 J/K (joules/kelvins). q = the electron charge = 1.6022 × 10-19 C (coulombs). T = the temperature in kelvins (K). This method can provide much improved absolute temperature measurement, but a lower resolution of 1.6 °C/LSB. The resulting equation to solve for T is: Where: ΔV = VBE (TEMP2) – VBE(TEMP1) (in mV) ∴ T = 2.648 ⋅ ΔV (in K) or T = 2.648 ⋅ ΔV – 273 (in °C) Temperature 1 and/or temperature 2 measurements have the same timing as Figure 44. 17 Submit Documentation Feedback |
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