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AD7781CRZ-REEL Datasheet(PDF) 1 Page - Analog Devices |
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AD7781CRZ-REEL Datasheet(HTML) 1 Page - Analog Devices |
1 / 16 page 20-Bit, Pin-Programmable, Low Power Sigma-Delta ADC AD7781 Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibilityis assumedbyAnalogDevicesforitsuse,norforanyinfringementsof patentsorother rightsofthirdpartiesthatmayresultfromitsuse.Specificationssubjecttochangewithoutnotice.No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2009 Analog Devices, Inc. All rights reserved. FEATURES Pin-programmable filter response Update rate: 10 Hz or 16.7 Hz Pin-programmable in-amp gain Pin-programmable power-down and reset Status function Internal clock oscillator Internal bridge power-down switch Current 115 μA typical (gain = 1) 330 μA typical (gain = 128) Simultaneous 50 Hz/60 Hz rejection Power supply: 2.7 V to 5.25 V −40°C to +105°C temperature range Independent interface power supply Packages 14-lead, narrow body SOIC 16-lead TSSOP 2-wire serial interface (read-only device) SPI compatible Schmitt trigger on SCLK APPLICATIONS Weigh scales Pressure measurement Industrial process control Portable instrumentation FUNCTIONAL BLOCK DIAGRAM A G = 1 OR 128 20-BIT Σ-Δ ADC DOUT/RDY GND VDD AIN(+) AIN(–) SCLK DVDD FILTER REFIN(+) GAIN REFIN(–) INTERNAL CLOCK AD7781 PDRST BPDSW Figure 1. Table 1. Parameter Gain = 128 Gain = 1 Output Data Rate 10 Hz 16.7 Hz 10 Hz 16.7 Hz RMS Noise C Grade 44 nV 65 nV 2.4 μV 2.7 μV B Grade 55 nV 90 nV 2.4 μV 2.7 μV P-P Resolution C Grade 17.6 17.1 18.8 18.7 B Grade 17.3 16.6 18.8 18.7 Settling Time 300 ms 120 ms 300 ms 120 ms GENERAL DESCRIPTION The AD7781 is a complete, low power front-end solution for bridge sensor products, including weigh scales, strain gages, and pressure sensors. It contains a precision, low power, 20-bit sigma-delta (Σ-Δ) ADC, an on-chip, low noise programmable gain amplifier (PGA), and an on-chip oscillator. Consuming only 330 μA, the AD7781 is particularly suitable for portable or battery-operated products where very low power is required. The AD7781 also has a power-down mode that allows the user to switch off the power to the bridge sensor and power down the AD7781 when not converting, thus increasing the battery life of the product. For ease of use, all the features of the AD7781 are controlled by dedicated pins. Each time that a data read occurs, eight status bits are appended to the 20-bit conversion. These status bits contain a pattern sequence that can be used to confirm the validity of the serial transfer. The on-chip PGA has a gain of 1 or 128, supporting a full-scale differential input of ±5 V or ±39 mV. The device has two filter response options. The filter response at the 16.7 Hz update rate provides superior dynamic performance. The settling time is 120 ms at this update rate. At the 10 Hz update rate, the filter response provides better than −45 dB of stop-band attenuation. In load cell applications, this stop-band rejection is useful to reject low frequency mechanical vibrations of the load cell. The settling time is 300 ms at this update rate. Simultaneous 50 Hz/ 60 Hz rejection occurs at both the 10 Hz and 16.7 Hz update rates. The AD7781 operates with a power supply from 2.7 V to 5.25 V. It is available in a narrow body, 14-lead SOIC package and in a 16-lead TSSOP package. |
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