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AD7715 Datasheet(PDF) 37 Page - Analog Devices |
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AD7715 Datasheet(HTML) 37 Page - Analog Devices |
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37 / 41 page  AD7715 Data Sheet Rev. E | Page 36 of 40 APPLICATIONS INFORMATION The AD7715 provides a low cost, high resolution analog-to- digital function. Because the analog-to-digital function is provided by a Σ-Δ architecture, it makes the part more immune to noisy environments thus making the part ideal for use in industrial and process control applications. It also provides a programmable gain amplifier, a digital filter and calibration options. Thus, it provides far more system level functionality than off-the-shelf integrating ADCs without the disadvantage of having to supply a high quality integrating capacitor. In addition, using the AD7715 in a system allows the system designer to achieve a much higher level of resolution because noise performance of the AD7715 is significantly better than that of the integrating ADCs. The on-chip PGA allows the AD7715 to handle an analog input voltage range as low as 10 mV full-scale with VREF = 1.25 V. The differential inputs of the part allow this analog input range to have an absolute value anywhere between AGND and AVDD when the part is operated in unbuffered mode. It allows the user to connect the transducer directly to the input of the AD7715. The programmable gain front end on the AD7715 allows the part to handle unipolar analog input ranges from 0 mV to 20 mV to 0 V to 2.5 V and bipolar inputs of ±20 mV to ±2.5 V. Because the part operates from a single supply, these bipolar ranges are with respect to a biased-up differential input. PRESSURE MEASUREMENT One typical application of the AD7715 is pressure measurement. Figure 14 shows the AD7715 used with a pressure transducer, the BP01 from Sensym. The pressure transducer is arranged in a bridge network and gives a differential output voltage between its OUT(+) and OUT(−) terminals. With rated full-scale pressure (in this case 300 mmHg) on the transducer, the differential output voltage is 3 mV/V of the input voltage (that is, the voltage between its IN(+) and IN(−) terminals). Assuming a 5 V excitation voltage, the full-scale output range from the transducer is 15 mV. The excitation voltage for the bridge is also used to generate the reference voltage for the AD7715. Therefore, variations in the excitation voltage do not introduce errors in the system. Choosing resistor values of 24 kΩ and 15 kΩ as per the diagram give a 1.92 V reference voltage for the AD7715 when the excitation voltage is 5 V. Using the part with a programmed gain of 128 results in the full-scale input span of the AD7715 being 15 mV which corresponds with the output span from the transducer. IN(–) OUT(+) IN(+) OUT(–) AUTO-ZEROED Σ-∆ MODULATOR CHARGE BALANCING ADC DIGITAL FILTER AVDD SERIAL INTERFACE REGISTER BANK MCLK IN MCLK OUT REF IN(+) REF IN(–) AGND DGND DOUT DIN CS SCLK DRDY RESET 24kΩ 15kΩ DVDD AD7715 +5V EXCITATION VOLTAGE = +5V AIN(+) AIN(–) A = 1 TO 128 PGA BUFFER CLOCK GENERATION Figure 14. Pressure Measurement Using the AD7715 |
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Similar Description - AD7715_17 |
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