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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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AD5421BREZ-REEL Fiches technique(PDF) 34 Page - Analog Devices |
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AD5421BREZ-REEL Fiches technique(HTML) 34 Page - Analog Devices |
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34 / 36 page  AD5421 Data Sheet Rev. F | Page 34 of 36 To determine the absolute worst-case overall error, the reference and RSET errors can be directly summed with the specified AD5421 maximum error. For example, when using an external reference and external RSET resistor, the maximum AD5421 error is 0.048% of full-scale range. Assuming that the absolute errors for the voltage reference and RSET resistor are, respectively, 0.04% and 0.05% with temperature coefficients of 3 ppm/°C and 2 ppm/°C, respectively, the overall worst-case error is as follows: Worst-Case Error = AD5421 Error + VREF Absolute Error + VREF TC + RSET Absolute Error + RSET TC Worst-Case Error = 0.048% + 0.04% + [(3/106) × 100 × 145]% + 0.05% + [(2/106) × 100 × 145]% = 0.21% FSR This is the absolute worst-case value when the AD5421 operates over the temperature range of −40°C to +105°C. An error of this value is very unlikely to occur because the temperature coeffi- cients of the individual components do not exhibit the same drift polarity, and, therefore, an element of cancelation occurs. For this reason, the TC values should be added in a root of squares fashion. A further improvement can be gained by performing a two-point calibration at zero scale and full scale, thus reducing the absolute errors of the voltage reference and RSET resistor to a combined error of 1 LSB or 0.0015% FSR. After performing this calibration, the total maximum error becomes Total Error = FSR % 102 . 0 %) 029 . 0 ( %) 0435 . 0 ( % 0015 . 0 % 048 . 0 2 2 = + + + To reduce this error value further, a voltage reference and RSET resistor with lower TC specifications must be chosen. THERMAL AND SUPPLY CONSIDERATIONS The AD5421 is designed to operate at a maximum junction temp- erature of 125°C. To ensure reliable and specified operation over the lifetime of the product, it is important that the device not be operated under conditions that cause the junction temperature to exceed this value. Excessive junction temperature can occur if the AD5421 experiences elevated voltages across its terminals while regulating the loop current at a high value. The resulting junction temperature depends on the ambient temperature. Table 24 provides the bounds of operation at maximum ambient temperature and maximum supply voltage. This information is displayed graphically in Figure 51 and Figure 52. These figures assume that the exposed paddle is connected to a copper plane of approximately 6 cm2. 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0 20 40 60 80 100 AMBIENT TEMPERATURE (°C) TSSOP LFCSP Figure 51. Maximum Power Dissipation vs. Ambient Temperature 60 50 40 30 20 10 0 40 50 60 70 80 90 100 AMBIENT TEMPERATURE (°C) LFCSP TSSOP Figure 52. Maximum Supply Voltage vs. Ambient Temperature Table 24. Thermal and Supply Considerations (External MOSFET Not Connected) Parameter Description 32-Lead LFCSP 28-Lead TSSOP Maximum Power Dissipation Maximum permitted power dissipation when operating at an ambient temperature of 105°C mW 500 40 105 125 = − = − JA A MAX J T T θ mW 625 32 105 125 = − = − JA A J MAX θ T T Maximum Ambient Temperature Maximum permitted ambient temperature when operating from a supply of 52 V while regulating a loop current of 22.8 mA = × − JA D MAX J P T θ ( ) ( ) C 77 40 0228 . 0 52 125 ° = × × − C 87 ) 32 ) 0228 . 0 52 (( 125 ) ( ° = × × − = × − JA D MAX J P T θ Maximum Supply Voltage Maximum permitted supply voltage when operating at an ambient temperature of 105°C while regulating a loop current of 22.8 mA V 21 40 0228 . 0 105 125 = × − = × − JA LOOP A MAX J I T T θ V 27 32 0228 . 0 105 125 = × − = × − JA LOOP A MAX J I T T θ |
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Description similaire - AD5421BREZ-REEL |
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