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AD22151YR Scheda tecnica(PDF) 5 Page - Analog Devices |
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AD22151YR Scheda tecnica(HTML) 5 Page - Analog Devices |
5 / 8 page AD22151 –5– REV. 0 the package is somewhat higher than the ambient temperature due to self-heating as a function of power dissipation. Second, package stress effect alters the specific operating parameters of the gain compensation, particularly the specific cross over temperature of TC1, TC3 ( ≈ ±10°C). CONFIGURATION AND COMPONENT SELECTION There are three areas of sensor operation that require external component selection. Temperature compensation (R1), signal gain (R2 and R3), and offset (R4). Temperature If the internal gain compensation is used, an external resistor is required to complete the gain TC circuit at Pin 3. A number of factors contribute to the value of this resistor. a. The intrinsic Hall cell sensitivity TC ≈ 950 ppm. b. Package induced stress variation in a. ≈ ±150 ppm. c. Specific field TC ≈ –200 ppm (Alnico), –2000 ppm (Ferrite), 0 ppm (electromagnet) etc. d. R1, TC. The final value of target compensation also dictates the use of either Pin 1 or Pin 2. Pin 1 is provided to allow for large nega- tive field TC such as ferrite magnets, thus R1 would be con- nected to Pins 1 and 3. Pin 2 uses an internal resistive TC to optimize smaller field coefficients such as Alnico, down to 0 ppm coefficients when only the sensor gain TC itself is dominant. The TC of R1 itself will also effect the compensation and as such a low TC resistor ( ±50 ppm) is recommended. Figures 10 and 11 indicate R1 resistor values and their associ- ated effectiveness for Pins 1 and 2 respectively. Note that the indicated drift response in both cases incorporates the intrinsic Hall sensitivity TC (BTCU). For example, the AD22151 sensor is to be used in conjunction with an Alnico material permanent magnet. The TC of such magnets is ≈ –200 ppm (see Figures 5 and 6). Figure 11 indi- cates that a compensating drift of +200 ppm at Pin 3 requires a nominal value of R1 = 18 k Ω (assuming negligible drift of R1 itself). R1 – k 3500 3000 1000 2500 1500 2000 0 5 10 20 25 500 0 15 30 Figure 10. Typical Resistor Value R1 vs. (Pins 1 and 3) Drift Compensation R1 – k 800 600 –200 400 0 200 0 5 10 20 25 –400 –600 15 30 35 40 45 50 Figure 11. Typical Resistor Value R1 (Pins 2 and 3) vs. Drift Compensation GAIN AND OFFSET The operation of the AD22151 can be bipolar (i.e., 0 Gauss = VCC/2) or a ratiometric offset can be implemented to Position Zero Gauss point at some other potential (i.e., 0.25 V). The gain of the sensor can be set by the appropriate R2 and R3 resistor values (see Figure 1) such that: Gain =1+ R3 R2 × 0.4 mV /G (1) However, if an offset is required to position the quiescent out- put at some other voltage then the gain relationship is modified to: Gain =1+ R3 (R2 R4) × 0.4 mV /G (2) The offset that R4 introduces is: Offset = R3 (R3 + R4) × V CC –V OUT () (3) For example: At VCC = 5 V at room temperature, the internal gain of the sensor is approximately 0.4 mV/Gauss. If a sensitivity of 6 mV/ Gauss is required with a quiescent output voltage of 1 V, the following calculations apply (see Figure 2 ). A value for R3 would be selected that complied with the various considerations of current and power dissipation, trim ranges (if applicable), etc. For the purpose of example assume a value of 85 k Ω. To achieve a quiescent offset of 1 V requires a value for R4 as: V CC 2 –1 V CC –1 = 0.375 (4) Thus: R4 = 85 k Ω 0.375 –85 k Ω=141.666 kΩ (5) The gain required would be 6/0.4 (mV/Gauss) = 15 |
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