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AD5662 Datasheet(PDF) 18 Page - Analog Devices |
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AD5662 Datasheet(HTML) 18 Page - Analog Devices |
18 / 24 page AD5662 Rev. A | Page 18 of 24 APPLICATIONS CHOOSING A REFERENCE FOR THE AD5662 To achieve the optimum performance from the AD5662, thought should be given to the choice of a precision voltage reference. The AD5662 has only one reference input, VREF. The voltage on the reference input is used to supply the positive input to the DAC. Therefore any error in the reference is reflected in the DAC. When choosing a voltage reference for high accuracy applica- tions, the sources of error are initial accuracy, ppm drift, long- term drift, and output voltage noise. Initial accuracy on the output voltage of the DAC leads to a full-scale error in the DAC. To minimize these errors, a reference with high initial accuracy is preferred. Also, choosing a reference with an output trim adjustment, such as the ADR423, allows a system designer to trim system errors out by setting a reference voltage to a voltage other than the nominal. The trim adjustment can also be used at temperature to trim out any error. Long-term drift is a measurement of how much the reference drifts over time. A reference with a tight long-term drift specification ensures that the overall solution remains relatively stable during its entire lifetime. The temperature coefficient of a reference’s output voltage effect INL, DNL, and TUE. A reference with a tight temperature coefficient specification should be chosen to reduce temperature dependence of the DAC output voltage in ambient conditions. In high accuracy applications, which have a relatively low noise budget, reference output voltage noise needs to be considered. It is important to choose a reference with as low an output noise voltage as practical for the system noise resolution required. Precision voltage references such as the ADR425 produce low output noise in the 0.1 Hz to10 Hz range. Examples of recom- mended precision references for use as supply to the AD5662 are shown in the Table 6. USING A REFERENCE AS A POWER SUPPLY FOR THE AD5662 Because the supply current required by the AD5662 is extremely low, an alternative option is to use a voltage reference to supply the required voltage to the part (see Figure 41). This is especially useful if the power supply is quite noisy, or if the system supply voltages are at some value other than 5 V or 3 V, for example, 15 V. The voltage reference outputs a steady supply voltage for the AD5662; see Table 6 for a suitable reference. If the low drop- out REF195 is used, it must supply 250 μA of current to the AD5662, with no load on the output of the DAC. When the DAC output is loaded, the REF195 also needs to supply the current to the load. The total current required (with a 5 kΩ load on the DAC output) is 250 μA + (5 V/5 kΩ) = 1.25 mA The load regulation of the REF195 is typically 2 ppm/mA, which results in a 2.5 ppm (12.5 μV) error for the 1.25 mA current drawn from it. This corresponds to a 0.164 LSB error. AD5662 3-WIRE SERIAL INTERFACE SYNC SCLK DIN +15V +5V 250 μA VOUT = 0V TO 5V VREF VDD REF195 Figure 41. REF195 as Power Supply to the AD5662 Table 6. Partial List of Precision References for Use with the AD5662 Part No. Initial Accuracy (mV max) Temp Drift (ppm oC max) 0.1 Hz to 10 Hz Noise (μV p-p typ) VOUT (V) ADR425 ±2 3 3.4 5 ADR395 ±6 25 5 5 REF195 ±2 5 50 5 AD780 ±2 3 4 2.5/3 ADR423 ±2 3 3.4 3 |
Similar Part No. - AD5662_15 |
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Similar Description - AD5662_15 |
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