Datasheet AD7781 (Analog Devices)
| Manufacturer | Analog Devices |
| Description | 20-Bit, Pin-Programmable, Ultralow Power Sigma-Delta ADC |
| Pages / Page | 17 / 1 — 20-Bit, Pin-Programmable,. Low Power Sigma-Delta ADC. AD7781. FEATURES. … |
| File Format / Size | PDF / 329 Kb |
| Document Language | English |
20-Bit, Pin-Programmable,. Low Power Sigma-Delta ADC. AD7781. FEATURES. FUNCTIONAL BLOCK DIAGRAM
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20-Bit, Pin-Programmable, Low Power Sigma-Delta ADC AD7781 FEATURES FUNCTIONAL BLOCK DIAGRAM Pin-programmable filter response GND AVDD GAIN REFIN(+) REFIN(–) Update rate: 10 Hz or 16.7 Hz Pin-programmable in-amp gain AIN(+) DOUT/RDY G = 1 20-BIT Σ-Δ Pin-programmable power-down and reset OR 128 ADC Status function AIN(–) SCLK Internal clock oscillator DVDD BPDSW INTERNAL CLOCK Internal bridge power-down switch FILTER
1 00
Current AD7781 PDRST
2- 16 08
115 μA typical (gain = 1)
Figure 1.
330 μA typical (gain = 128) Simultaneous 50 Hz/60 Hz rejection Table 1. Power supply: 2.7 V to 5.25 V Parameter Gain = 128 Gain = 1 −40°C to +105°C temperature range
Output Data Rate 10 Hz 16.7 Hz 10 Hz 16.7 Hz
Independent interface power supply
RMS Noise
Packages
C Grade 44 nV 65 nV 2.4 μV 2.7 μV
14-lead, narrow body SOIC
B Grade 55 nV 90 nV 2.4 μV 2.7 μV
16-lead TSSOP
P-P Resolution
2-wire serial interface (read-only device)
C Grade 17.6 17.1 18.8 18.7
SPI compatible
B Grade 17.3 16.6 18.8 18.7
Schmitt trigger on SCLK
Settling Time 300 ms 120 ms 300 ms 120 ms
APPLICATIONS Weigh scales Pressure measurement Industrial process control Portable instrumentation GENERAL DESCRIPTION
The AD7781 is a complete, low power front-end solution for The on-chip PGA has a gain of 1 or 128, supporting a full-scale bridge sensor products, including weigh scales, strain gages, differential input of ±5 V or ±39 mV. The device has two filter and pressure sensors. It contains a precision, low power, 20-bit response options. The filter response at the 16.7 Hz update rate sigma-delta (Σ-Δ) ADC, an on-chip, low noise programmable provides superior dynamic performance. The settling time is gain amplifier (PGA), and an on-chip oscillator. 120 ms at this update rate. At the 10 Hz update rate, the filter Consuming only 330 μA, the AD7781 is particularly suitable for response provides better than −45 dB of stop-band attenuation. portable or battery-operated products where very low power is In load cell applications, this stop-band rejection is useful to required. The AD7781 also has a power-down mode that allows reject low frequency mechanical vibrations of the load cell. The the user to switch off the power to the bridge sensor and power settling time is 300 ms at this update rate. Simultaneous 50 Hz/ down the AD7781 when not converting, thus increasing the 60 Hz rejection occurs at both the 10 Hz and 16.7 Hz update rates. battery life of the product. The AD7781 operates with a power supply from 2.7 V to 5.25 V. For ease of use, all the features of the AD7781 are controlled by It is available in a narrow body, 14-lead SOIC package and in a dedicated pins. Each time that a data read occurs, eight status bits 16-lead TSSOP package. 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.
Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Tel: 781.329.4700 www.analog.com Trademarks and registered trademarks are the property of their respective owners. Fax: 781.461.3113 ©2009 Analog Devices, Inc. All rights reserved.
Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS TIMING CHARACTERISTICS Circuit and Timing Diagrams ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS OUTPUT NOISE AND RESOLUTION THEORY OF OPERATION FILTER, DATA RATE, AND SETTLING TIME GAIN POWER-DOWN/RESET (PDRST) ANALOG INPUT CHANNEL BIPOLAR CONFIGURATION DATA OUTPUT CODING REFERENCE BRIDGE POWER-DOWN SWITCH DIGITAL INTERFACE APPLICATIONS INFORMATION WEIGH SCALES AD7781 PERFORMANCE IN A WEIGH SCALE SYSTEM EMI RECOMMENDATIONS GROUNDING AND LAYOUT OUTLINE DIMENSIONS ORDERING GUIDE
1 00
Current AD7781 PDRST
2- 16 08
115 μA typical (gain = 1)
Figure 1.
330 μA typical (gain = 128) Simultaneous 50 Hz/60 Hz rejection Table 1. Power supply: 2.7 V to 5.25 V Parameter Gain = 128 Gain = 1 −40°C to +105°C temperature range
Output Data Rate 10 Hz 16.7 Hz 10 Hz 16.7 Hz
Independent interface power supply
RMS Noise
Packages
C Grade 44 nV 65 nV 2.4 μV 2.7 μV
14-lead, narrow body SOIC
B Grade 55 nV 90 nV 2.4 μV 2.7 μV
16-lead TSSOP
P-P Resolution
2-wire serial interface (read-only device)
C Grade 17.6 17.1 18.8 18.7
SPI compatible
B Grade 17.3 16.6 18.8 18.7
Schmitt trigger on SCLK
Settling Time 300 ms 120 ms 300 ms 120 ms
APPLICATIONS Weigh scales Pressure measurement Industrial process control Portable instrumentation GENERAL DESCRIPTION
The AD7781 is a complete, low power front-end solution for The on-chip PGA has a gain of 1 or 128, supporting a full-scale bridge sensor products, including weigh scales, strain gages, differential input of ±5 V or ±39 mV. The device has two filter and pressure sensors. It contains a precision, low power, 20-bit response options. The filter response at the 16.7 Hz update rate sigma-delta (Σ-Δ) ADC, an on-chip, low noise programmable provides superior dynamic performance. The settling time is gain amplifier (PGA), and an on-chip oscillator. 120 ms at this update rate. At the 10 Hz update rate, the filter Consuming only 330 μA, the AD7781 is particularly suitable for response provides better than −45 dB of stop-band attenuation. portable or battery-operated products where very low power is In load cell applications, this stop-band rejection is useful to required. The AD7781 also has a power-down mode that allows reject low frequency mechanical vibrations of the load cell. The the user to switch off the power to the bridge sensor and power settling time is 300 ms at this update rate. Simultaneous 50 Hz/ down the AD7781 when not converting, thus increasing the 60 Hz rejection occurs at both the 10 Hz and 16.7 Hz update rates. battery life of the product. The AD7781 operates with a power supply from 2.7 V to 5.25 V. For ease of use, all the features of the AD7781 are controlled by It is available in a narrow body, 14-lead SOIC package and in a dedicated pins. Each time that a data read occurs, eight status bits 16-lead TSSOP package. 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.
Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Tel: 781.329.4700 www.analog.com Trademarks and registered trademarks are the property of their respective owners. Fax: 781.461.3113 ©2009 Analog Devices, Inc. All rights reserved.
Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS TIMING CHARACTERISTICS Circuit and Timing Diagrams ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS OUTPUT NOISE AND RESOLUTION THEORY OF OPERATION FILTER, DATA RATE, AND SETTLING TIME GAIN POWER-DOWN/RESET (PDRST) ANALOG INPUT CHANNEL BIPOLAR CONFIGURATION DATA OUTPUT CODING REFERENCE BRIDGE POWER-DOWN SWITCH DIGITAL INTERFACE APPLICATIONS INFORMATION WEIGH SCALES AD7781 PERFORMANCE IN A WEIGH SCALE SYSTEM EMI RECOMMENDATIONS GROUNDING AND LAYOUT OUTLINE DIMENSIONS ORDERING GUIDE
