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AD571K Folha de dados(PDF) 4 Page - Analog Devices |
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AD571K Folha de dados(HTML) 4 Page - Analog Devices |
4 / 8 page AD571 REV. A –4– BIT 9 BIT 8 BIT 10 (LSB) DATA READY BIT 5 BIT 4 BIT 3 ANALOG IN V– BIT 7 BIT 6 DIGITAL COM BIT 2 BLK AND CONV (MSB) BIT 1 V+ ANALOG COM BIPOLAR OFF 1 2 18 17 5 6 7 14 13 12 3 4 16 15 8 11 9 10 TOP VIEW (Not to Scale) AD571 Figure 3. AD571 Pin Connections FULL-SCALE CALIBRATION The 5 k Ω thin-film input resistor is laser trimmed to produce a current which matches the full-scale current of the internal DAC—plus about 0.3%—when a full-scale analog input voltage of 9.990 volts (10 volts—1 LSB) is applied at the input. The in- put resistor is trimmed in this way so that if a fine trimming po- tentiometer is inserted in series with the input signal, the input current at the full-scale input voltage can be trimmed down to match the DAC full-scale current as precisely as desired. How- ever, for many applications the nominal 9.99 volt full scale can be achieved to sufficient accuracy by simply inserting a 15 Ω re- sistor in series with the analog input to Pin 13. Typical full-scale calibration error will then be about ±2 LSB or ±0.2%. If a more precise calibration is desired, a 50 Ω trimmer should be used in- stead. Set the analog input at 9.990 volts, and set the trimmer so that the output code is just at the transition between 1111111110 and 1111111111. Each LSB will then have a weight of 9.766 mV. If a nominal full scale of 10.24 volts is desired (which makes the LSB have a value of exactly 10.00 mV), a 100 Ω resistor in series with a 100 Ω trimmer (or a 200 Ω trim- mer with good resolution) should be used. Of course, larger full-scale ranges can be arranged by using a larger input resistor, but linearity and full-scale temperature coefficient may be com- promised if the external resistor becomes a sizable percentage of 5 k Ω. BIT 9 BIT 8 BIT 10 (LSB) DATA READY BIT 5 BIT 4 BIT 3 ANALOG IN –15V BIT 7 BIT 6 DIGITAL COM BIT 2 BLK AND CONV (MSB) BIT 1 ANALOG COM BIPOLAR CONTROL 1 2 18 17 5 6 7 14 13 12 3 4 16 15 8 11 9 10 TOP VIEW (Not to Scale) AD571 +5V (TOLERATES 200mV TO DIGITAL COM) RIN 15 Ω FIXED OR 50 Ω VARIABLE (SEE TEXT) (SHORT TO COM FOR UNIPOLAR, OPEN FOR BIPOLAR) Figure 4. Standard AD571 Connections BIPOLAR OPERATION The standard unipolar 0 V to +10 V range is obtained by short- ing the bipolar offset control pin to digital common. If the pin is left open, the bipolar offset current will be switched into the comparator summing node, giving a –5 V to +5 V range with an offset binary output code. (–5.00 volts in will give a 10-bit code of 0000000000; an input of 0.00 volts results in an output code of 1000000000 and 4.99 volts at the input yields the 1111111111). The bipolar offset control input is not directly TTL compatible, but a TTL interface for logic control can be constructed as shown in Figure 5. AD571 B & C DR DATA DCOM ACOM AIN BIPOLAR OFFSET CONTROL TTL GATE 10 BITS 5V COM +5V 15V COM 30k Ω 3x IN4148 USE ACTIVE PULL-UP GATE –15V Figure 5. Bipolar Offset Controlled by Logic Gate Gate Output = 1: Unipolar 0 V–10 V Input Range Gate Output = 0: Bipolar ±5 V Input Range COMMON-MODE RANGE The AD571 provides separate analog and digital common con- nections. The circuit will operate properly with as much as ±200 mV of common-mode range between the two commons. This permits more flexible control of system common bussing and digital and analog returns. In normal operation the analog common terminal may generate transient currents of up to 2 mA during a conversion. In addi- tion, a static current of about 2 mA will flow into analog com- mon in the unipolar mode after a conversion is complete. An additional 1 mA will flow in during a blank interval with zero analog input. The analog common current will be modulated by the variations in input signal. The absolute maximum voltage rating between the two com- mons is ±1 volt. We recommend that a parallel pair of back-to- back protection diodes can be connected between the commons if they are not connected locally. TEMPERATURE – °C 11 3 –50 125 –25 0 25 50 70 100 10 7 6 5 4 9 8 2 1.5 1 I +15V,C I –15V,B I –15V,C I +15V,B I +5V,C I +5V,B C = CONVERT MODE B = BLANK MODE Figure 6. AD571 Power Supply Current vs. Temperature |
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