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AD7840ARS 数据表(PDF) 5 Page - Analog Devices |
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AD7840ARS 数据表(HTML) 5 Page - Analog Devices |
5 / 16 page AD7840 REV. B –5– PIN CONFIGURATIONS DIP/SSOP PLCC for external use, it should he decoupled to AGND with a 200 Ω resistor in series with a parallel combination of a 10 µF tantalum capacitor and a 0.1 µF ceramic capacitor. Figure 2. Internal Reference EXTERNAL REFERENCE In some applications, the user may require a system reference or some other external reference to drive the AD7840 reference in- put. Figure 3 shows how the AD586 5 V reference can be con- ditioned to provide the 3 V reference required by the AD7840 REF IN. An alternate source of reference voltage for the AD7840 in systems which use both a DAC and an ADC is to use the REF OUT voltage of ADCs such as the AD7870 and AD7871. A circuit showing this arrangement is shown in Figure 20. Figure 3. AD586 Driving AD7840 REF IN D/A SECTION The AD7840 contains a 14-bit voltage mode D/A converter consisting of highly stable thin film resistors and high speed NMOS single-pole, double-throw switches. The simplified cir- cuit diagram for the DAC section is shown in Figure 1. The three MSBs of the data word are decoded to drive the seven switches A–G. The 11 LSBs switch an 11-bit R-2R ladder struc- ture. The output voltage from this converter has the same polar- ity as the reference voltage, REF IN. The REF IN voltage is internally buffered by a unity gain ampli- fier before being applied to the D/A converter and the bipolar bias circuitry. The D/A converter is configured and sealed for a 3 V reference and the device is tested with 3 V applied to REF IN. Operating the AD7840 at reference voltages outside the ±5% tolerance range may result in degraded performance from the part. Figure 1. DAC Ladder Structure INTERNAL REFERENCE The AD7840 has an on-chip temperature compensated buried Zener reference (see Figure 2) which is factory trimmed to 3 V ±10 mV. The reference voltage is provided at the REF OUT pin. This reference can be used to provide both the reference voltage for the D/A converter and the bipolar bias circuitry. This is achieved by connecting the REF OUT pin to the REF IN pin of the device. The reference voltage can also be used as a reference for other components and is capable of providing up to 500 µA to an ex- ternal load. The maximum recommended capacitance on REF OUT for normal operation is 50 pF. If the reference is required |
类似零件编号 - AD7840ARS |
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类似说明 - AD7840ARS |
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