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AD22100STZ Folha de dados(PDF) 8 Page - Analog Devices |
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AD22100STZ Folha de dados(HTML) 8 Page - Analog Devices |
8 / 12 page AD22100 Rev. D | Page 8 of 12 Due to its limited current sinking ability, the AD22100 is inca- pable of driving loads to the V+ power supply and is instead intended to drive grounded loads. A typical value for short- circuit current limit is 7 mA, so devices can reliably source 1 mA or 2 mA. However, for best output voltage accuracy and minimal internal self-heating, output current should be kept below 1 mA. Loads connected to the V+ power supply should be avoided as the current sinking capability of the AD22100 is fairly limited. These considerations are typically not a problem when driving a microcontroller analog-to-digital converter input pin (see the Microprocessor A/D Interface Issues section). RATIOMETRICITY CONSIDERATIONS The AD22100 will operate with slightly better accuracy than that listed in the data sheet specifications if the power supply is held constant. This is because the AD22100’s output voltage varies with both temperature and supply voltage, with some errors. The ideal transfer function describing output voltage is: (V+/5 V) × (1.375 V + 22.5 mV/°C × TA) The ratiometricity error is defined as the percent change away from the ideal transfer function as the power supply voltage changes within the operating range of 4 V to 6.5 V. For the AD22100, this error is typically less than 1%. A movement from the ideal transfer function by 1% at 25°C, with a supply voltage varying from 5.0 V to 5.50 V, results in a 1.94 mV change in output voltage or 0.08°C error. This error term is greater at higher temperatures because the output (and error term) is directly proportional to temperature. At 150°C, the error in output voltage is 4.75 mV or 0.19°C. For example, with VS = 5.0 V, and TA = +25°C, the nominal output of the AD22100 will be 1.9375 V. At VS = 5.50 V, the nominal output will be 2.1313 V, an increase of 193.75 mV. A proportionality error of 1% is applied to the 193.75 mV, yielding an error term of 1.9375 mV. This error term translates to a variation in output voltage of 2.1293 V to 2.3332 V. A 1.94 mV error at the output is equivalent to about 0.08°C error in accuracy. If 150°C is substituted for 25°C in the above example, the error term translates to a variation in output voltage of 5.2203 V to 5.2298 V. A 4.75 mV error at the output is equivalent to about 0.19°C error in accuracy. MOUNTING CONSIDERATIONS If the AD22100 is thermally attached and properly protected, it can be used in any measuring situation where the maximum range of temperatures encountered is between −50°C and +150°C. Because plastic IC packaging technology is employed, excessive mechanical stress must be avoided when fastening the device with a clamp or screw-on heat tab. Thermally conductive epoxy or glue is recommended for typical mounting conditions. In wet or corrosive environments, an electrically isolated metal or ceramic well should be used to shield the AD22100. Because the part has a voltage output (as opposed to current), it offers modest immunity to leakage errors, such as those caused by condensation at low temperatures. THERMAL ENVIRONMENT EFFECTS The thermal environment in which the AD22100 is used determines two performance traits: the effect of self-heating on accuracy and the response time of the sensor to rapid changes in temperature. In the first case, a rise in the IC junction temperature above the ambient temperature is a function of two variables: the power consumption of the AD22100 and the thermal resistance between the chip and the ambient environ- ment θJA. Self-heating error in °C can be derived by multiplying the power dissipation by θJA. Because errors of this type can vary widely for surroundings with different heat-sinking capaci- ties, it is necessary to specify θJA under several conditions. Table 6 shows how the magnitude of self-heating error varies relative to the environment. A typical part will dissipate about 2.2 mW at room temperature with a 5 V supply and negligible output loading. Table 6 indicates a θJA of 190°C/W in still air, without a heat sink, yielding a temperature rise of 0.4°C. Thermal rise will be considerably less in either moving air or with direct physical connection to a solid (or liquid) body. Table 6. Thermal Resistance (TO-92) Medium θJA (°C/W) t (sec)1 Aluminum Block 60 2 Moving Air2 Without Heat Sink 75 3.5 Still Air Without Heat Sink 190 15 |
Nº de peça semelhante - AD22100STZ |
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Descrição semelhante - AD22100STZ |
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