Low Power, 2-Channel 24-Bit Sigma-Delta ADC Data Sheet AD7787 FEATURES APPLICATIONS Power Smart transmitters Supply: 2.5 V to 5.25 V operation Battery applications Normal mode: 75 A max Portable instrumentation Power-down mode: 1 A max Sensor measurement RMS noise: 1.1 V at 9.5 Hz update rate Temperature measurement 19.5-bit p-p resolution (22 bits effective resolution) Pressure measurement Integral nonlinearity: 3.5 ppm typical Weigh scales Simultaneous 50 Hz and 60 Hz rejection 4 to 20 mA loops Internal clock oscillator GENERAL DESCRIPTION Rail-to-rail input buffer VDD monitor channel The AD7787 is a low power, complete analog front end for low Temperature range: 40C to +105C frequency measurement applications. It contains a low noise 10-lead MSOP 24-bit - ADC with one differential input and one single- ended input that can be buffered or unbuffered. INTERFACE The device operates from an internal clock. Therefore, the user 3-wire serial does not have to supply a clock source to the device. The output SPI, QSPI, MICROWIRE, and DSP compatible data rate from the part is software programmable and can be Schmitt trigger on SCLK varied from 9.5 Hz to 120 Hz, with the rms noise equal to 1.1 V at the lower update rate. The internal clock frequency can be divided by a factor of 2, 4, or 8, which leads to a reduction in the current consumption. The update rate, cutoff frequency, and settling time scales with the clock frequency. The part operates with a power supply from 2.5 V to 5.25 V. When operating from a 3 V supply, the power dissipation for the part is 225 W maximum. It is housed in a 10-lead MSOP. FUNCTIONAL BLOCK DIAGRAM GND V REFIN DD AD7787 V DD DOUT/RDY SERIAL DIN INTERFACE AND AIN1(+) SCLK - LOGIC BUF MUX ADC CONTROL AIN1() CS AIN2 CLOCK GND Figure 1. Rev. A 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 20042013 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. 04477-0-001AD7787 Data Sheet TABLE OF CONTENTS Specif icat ions ..................................................................................... 3 Overview ..................................................................................... 14 Timing Characteristics ..................................................................... 5 Noise Performance ..................................................................... 14 Absolute Maximum Ratings ............................................................ 7 Reduced Current Modes ........................................................... 14 ESD Caution .................................................................................. 7 Digital Interface .......................................................................... 15 Pin Configuration and Function Descriptions ............................. 8 Circuit Description......................................................................... 18 Typical Performance Characteristics ............................................. 9 Analog Input Channel ............................................................... 18 On-Chip Registers .......................................................................... 10 Bipolar/Unipolar Configuration .............................................. 18 Communications Register (RS1, RS0 = 0, 0) .......................... 10 Data Output Coding .................................................................. 18 Status Register (RS1, RS0 = 0, 0 Power-On/Reset Reference Input ........................................................................... 18 = 08C) ........................................................................................ 11 VDD Monitor ................................................................................ 19 Mode Register (RS1, RS0 = 0, 1 Power-On/Reset Grounding and Layout .............................................................. 19 = 002) ......................................................................................... 12 Applications ................................................................................ 19 Filter Register (RS1, RS0 = 1, 0 Power-On/Reset = 004) ......................................................................................... 13 Outline Dimensions ....................................................................... 20 Data Register (RS1, RS0 = 1, 1 Power-On/Reset Ordering Guide .......................................................................... 20 = 0000000) ................................................................................ 13 ADC Circuit Information .............................................................. 14 REVISION HISTORY 3/13Rev. 0 to Rev. A Changes to Figure 13 ....................................................................... 15 Change to Reference Input Section ............................................... 18 Updated Outline Dimensions ........................................................ 20 Changes to Ordering Guide ........................................................... 20 4/04Revision 0: Initial Version Rev. A Page 2 of 20