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AD7249BR 数据表(PDF) 6 Page - Analog Devices |
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AD7249BR 数据表(HTML) 6 Page - Analog Devices |
6 / 12 page REV. C –6– AD7249 Internal Reference The AD7249 has an on-chip temperature compensated buried Zener reference which is factory trimmed to 5 V ± 50 mV. The reference voltage is provided at the REFOUT pin. This refer- ence can be used to provide the reference voltage for the D/A converter by connecting the REFOUT pin to the REFIN pin. The reference voltage can also be used as a reference for other components and is capable of providing up to 500 µA to an external load. The maximum recommended capacitance on REFOUT for normal operation is 50 pF. If the reference output is required to drive a capacitive load greater than 50 pF, then a 200 Ω resistor should be placed in series with the capacitive load. Figure 3 shows the suggested REF OUT decoupling scheme, a 200 Ω resistor and the parallel combination of a 10 µF tantalum and a 0.1 µF ceramic capacitor. This decoupling scheme reduces the noise spectral density of the reference. REFOUT 200 10 F 0.1 F EXT LOAD Figure 3. Reference Decoupling Scheme External Reference In some applications, the user may require a system reference or some other external reference to drive the AD7249. References such as the AD586 provide an ideal external reference source (See Figure 10). The REFIN voltage is internally buffered by a unity gain amplifier before being applied to the D/A converter. The D/A converter is scaled for a 5 V reference and the device is tested with 5 V applied to REFIN. Other reference voltages may be used with degraded performance. Figure 4 shows the degra- dation in linearity vs. REFIN. REFIN – Volts 1.0 2 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 3 4567 8 9 VDD = +15V VSS = –15V TA = +25 C INL DNL Figure 4. Linearity vs. REFIN Voltage Op Amp Section The output of the voltage-mode D/A converter is buffered by a noninverting CMOS amplifier. The ROFS input allows three output voltage ranges to be selected. The buffer amplifier is capable of developing +10 V across a 2 k Ω load to AGND. The output amplifier can be operated from a single +15 V sup- ply by tying VSS = 0 V. The amplifier can also be operated from dual supplies to allow an additional bipolar output range of –5 V to +5 V. Dual sup- plies are necessary for the bipolar output range but can also be used for the unipolar ranges to give faster settling time to volt- ages near 0 V, to allow full sink capability of 2.5 mA over the entire output range and to eliminate the effects of negative offsets on the transfer characteristic (outlined previously). A plot of the output sink capability of the amplifier is shown in Figure 5. OUTPUT VOLTAGE – Volts 3 0 2 1 0 2 468 10 VSS = 0V VSS = –15V Figure 5. Amplifier Sink Current FREQUENCY – Hz 500 50 100 200 500 1k 2k 5k 10k VDD = +15V VSS = 0V TA = +25 C 200 100 50 20 0 REFERENCE DECOUPLING COMPONENTS ARE A 200 RESISTOR IN SERIES WITH A PARALLEL COMBINATION OF 10 F AND 0.1 F TO GND. * 20k 50k 100k REFERENCE (NO DECOUPLING) REFERENCE (DECOUPLED*) OUTPUT WITH ALL 0s ON DAC Figure 6. Noise Spectral Density vs. Frequency |
类似零件编号 - AD7249BR |
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类似说明 - AD7249BR |
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