Low Power, 16-/24-Bit Sigma-Delta ADC for Bridge Sensors Low Power, 16-/24-Bit Data Sheet AD7796/AD7797 FEATURES FUNCTIONAL BLOCK DIAGRAM AV REFIN(+) REFIN() GND DD RMS noise: 65 nV Instrumentation amp AD7796: 16-BIT ADC AV DD AD7797: 24-BIT ADC Temperature sensor SERIAL DOUT/RDY AIN(+) Internal clock oscillator INTERFACE DIN AIN() - 128 AND MUX ADC SCLK Simultaneous 50 Hz/60 Hz rejection CONTROL LOGIC CS Update rate range: 4.17 Hz to 123 Hz GND REFERENCE Current: 250 A typ DV INTERNAL DD TEMP CLOCK Power-down: 1 A AD7796/ SENSOR AD7797 Power supply range: 2.7 V to 5.25 V CLK 40C to +85C temperature range Figure 1. Independent interface power supply 16-lead TSSOP INTERFACE 3-wire serial SPI, QSPI, MICROWIRE, and DSP compatible Schmitt trigger on SCLK APPLICATIONS Weigh scales Strain gages Industrial process control Instrumentation Portable instrumentation GENERAL DESCRIPTION The AD7796/AD7797 are complete, analog front ends for high The devices can be operated with the internal clock or an external precision, bridge sensor applications such as weigh scales. The clock. The output data rate from the devices is software- AD7796/AD7797 contain a - ADC capable of 16 -/24-bit programmable and can be varied from 4.17 Hz to 123 Hz. resolution, respectively. The on-chip instrumentation amplifier The AD7796/AD7797 operate with a power supply from 2.7 V has a fixed gain of 128, allowing small amplitude signals such as to 5.25 V. Each device consumes a current of 250 A typical and those from bridge sensors to be directly interfaced to the ADC. is housed in a 16-lead TSSOP. Each device has one differential input and contains a temperature sensor that is internally connected to the ADC. This sensor can be used to perform temperature compensation of the bridge. Rev. B Document Feedback 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 Tel: 781.329.4700 20062016 Analog Devices, Inc. All rights reserved. license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Technical Support www.analog.com Trademarks and registered trademarks are the property of their respective owners. 06083-001AD7796/AD7797 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 ID Register................................................................................... 14 Interface ............................................................................................. 1 Offset Register ............................................................................ 15 Applications ....................................................................................... 1 Full-Scale Register ...................................................................... 15 Functional Block Diagram .............................................................. 1 ADC Circuit Information .............................................................. 16 General Description ......................................................................... 1 Overview ..................................................................................... 16 Revision History ............................................................................... 2 Digital Interface .......................................................................... 17 Specifications ..................................................................................... 3 Circuit Description......................................................................... 20 Timing Characteristics ..................................................................... 5 Analog Input Channel ............................................................... 20 Timing Diagrams .......................................................................... 6 Bipolar/Unipolar Configuration .............................................. 20 Absolute Maximum Ratings ............................................................ 7 Data Output Coding .................................................................. 20 Thermal Resistance ...................................................................... 7 Reference ..................................................................................... 20 ESD Caution .................................................................................. 7 Reset ............................................................................................. 21 Pin Configuration and Function Descriptions ............................. 8 Burnout Currents ....................................................................... 21 RMS Noise and Resolution Specifications .................................... 9 AV Monitor ............................................................................. 21 DD Typical Performance Characteristics ........................................... 10 Temperature Monitor ................................................................ 21 On-Chip Registers .......................................................................... 11 Calibration ................................................................................... 21 Communication Register .......................................................... 11 Grounding and Layout .............................................................. 22 Status Register ............................................................................. 12 Applications Information .............................................................. 23 Mode Register ............................................................................. 12 Weigh Scales ................................................................................ 23 Configuration Register .............................................................. 14 Outline Dimensions ....................................................................... 24 Data Register ............................................................................... 14 Ordering Guide .......................................................................... 24 REVISION HISTORY 3/16Rev. A to Rev. B Changes to RS2, RS1, RS0 = 0, 0, 0 Power-On/Reset = 0x80 Section and Table 11 ....................................................................... 12 8/06Rev. 0 to Rev. A Changes to Table 1 ............................................................................ 3 Changes to Figure 5 .......................................................................... 8 Changes to Table 14 ........................................................................ 13 7/06Revision 0: Initial Version Rev. B Page 2 of 24