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AD558JD датащи(PDF) 6 Page - Analog Devices |
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AD558JD датащи(HTML) 6 Page - Analog Devices |
6 / 8 page AD558 REV. A –6– tW 2.0V 2.0V 0.8V 0.8V tDS tDH DATA INPUTS CS OR CE tSETTLING 1/2 LSB DAC V OUTPUT tW = STORAGE PULSE WIDTH = 200ns MIN t DH = DATA HOLD TIME = 10ns MIN t DS = DATA SETUP TIME = 200ns MIN t SETTLING = DAC OUTPUT SETTLING TIME TO ±1/2 LSB Figure 7. AD558 Timing USE OF VOUT SENSE Separate access to the feedback resistor of the output amplifier allows additional application versatility. Figure 8a shows how I × R drops in long lines to remote loads may be cancelled by putting the drops “inside the loop.” Figure 8b shows how the separate sense may be used to provide a higher output current by feeding back around a simple current booster. 15 16 AD558 12 13 VOUT 14 RL GND GAIN SELECT SENSE VOUT VOUT 0V TO +10V a. Compensation for I × R Drops in Output Lines 15 16 AD558 12 13 VOUT RL GND GAIN SELECT SENSE VOUT VOUT 0V TO +2.56V VCC 2N2222 14 b. Output Current Booster Figure 8. Use of VOUT Sense OPTIMIZING SETTLING TIME In order to provide single-supply operation and zero-based output voltage ranges, the AD558 output stage has a passive “pull-down” to ground. As a result, settling time for negative going output steps may be longer than for positive-going output steps. The relative difference depends on load resistance and capacitance. If a negative power supply is available, the negative-going settling time may be improved by adding a pull- down resistor from the output to the negative supply as shown in Figure 9. The value of the resistor should be such that, at zero voltage out, current through that resistor is 0.5 mA max. BIPOLAR OUTPUT RANGES The AD558 was designed for operation from a single power supply and is thus capable of providing only unipolar (0 V to +2.56 V and 0 V to 10 V) output ranges. If a negative supply is 15 16 AD558 VOUT RL SENSE VOUT VEE NEGATIVE SUPPLY RP-D = 2x VEE (in k Ω) Figure 9. Improved Settling Time available, bipolar output ranges may be achieved by suitable output offsetting and scaling. Figure 10 shows how a ±1.28 volt output range may be achieved when a –5 volt power supply is available. The offset is provided by the AD589 precision 1.2 volt reference which will operate from a +5 volt supply. The AD544 output amplifier can provide the necessary ±1.28 volt output swing from ±5 volt supplies. Coding is complementary offset binary. 14 15 16 AD558 12 13 AD589 AD544 0.01 µF 0.01 µF 0.01 µF –5V –1.2V 4.7k Ω 5k Ω 4.53k Ω –5V INPUT CODE V OUT 00000000 +128V 10000000 0V 11111111 –1.27V 1.5k Ω V O +1.28 TO –1.27 5k Ω +5V 500 Ω BIPOLAR OFFSET ADJUST V IN V OUT = 0V TO +2.56V Figure 10. Bipolar Operation of AD558 from ±5 V Supplies MEASURING OFFSET ERROR One of the most commonly specified endpoint errors associated with real-world nonideal DACs is offset error. In most DAC testing, the offset error is measured by applying the zero-scale code and measuring the output deviation from 0 volts. There are some DACs, like the AD558 where offset errors may be present but not observable at the zero scale, because of other circuit limitations (such as zero coinciding with single- supply ground) so that a nonzero output at zero code cannot be read as the offset error. Factors like this make testing the AD558 a little more complicated. By adding a pulldown resistor from the output to a negative supply as shown in Figure 11, we can now read offset errors at zero code that may not have been observable due to circuit limitations. The value of the resistor should be such that, at zero voltage out, current through the resistor is 0.5 mA max. OUTPUT AMP 16 15 14 13 AGND VOUT SELECT VOUT SENSE VOUT –V 0.5mA a. 0 V to 2.56 V Output Range |
Аналогичный номер детали - AD558JD |
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Аналогичное описание - AD558JD |
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