6-Channel, Low Noise, Low Power, 24-/16-Bit - ADC with On-Chip In-Amp and Reference AD7794/AD7795 FEATURES Industrial process control Instrumentation Up to 23 effective bits Blood analysis RMS noise: 40 nV 4.17 Hz, 85 nV 16.7 Hz Smart transmitters Current: 400 A typical Liquid/gas chromatography Power-down: 1 A maximum 6-digit DVM Low noise, programmable gain, instrumentation amp Band gap reference with 4 ppm/C drift typical GENERAL DESCRIPTION Update rate: 4.17 Hz to 470 Hz The AD7794/AD7795 are low power, low noise, complete Six differential analog inputs analog front ends for high precision measurement applications. Internal clock oscillator They contain a low noise, 24-/16-bit - ADC with six Simultaneous 50 Hz/60 Hz rejection differential inputs. The on-chip low noise instrumentation Reference detect amplifier means that signals of small amplitude can be Programmable current sources interfaced directly to the ADC. On-chip bias voltage generator Each device contains a precision, low noise, low drift internal Burnout currents band gap reference, and can also accept up to two external Low-side power switch differential references. Other on-chip features include Power supply: 2.7 V to 5.25 V Temperature range: programmable excitation current sources, burnout currents, B grade: 40C to +105C and a bias voltage generator that is used to set the common- C grade: 40C to +125C mode voltage of a channel to AVDD/2. The low-side power Independent interface power supply switch can be used to power down bridge sensors between 24-lead TSSOP conversions, minimizing the systems power consumption. The 3-wire serial interface AD7794/AD7795 can operate with either an internal clock or SPI, QSPI, MICROWIRE, and DSP compatible an external clock. The output data rate from each part can vary Schmitt trigger on SCLK from 4.17 Hz to 470 Hz. Both parts operate with a power supply from 2.7 V to 5.25 V. APPLICATIONS The B-grade parts (AD7794 and AD7795) are specified for a Temperature measurement temperature range of 40C to +105C while the C-grade part Pressure measurement (AD7794) is specified for a temperature range of 40C to Weigh scales +125C. They consume a current of 400 A typical and are Strain gage transducers housed in a 24-lead TSSOP. Gas analysis FUNCTIONAL BLOCK DIAGRAM GND AV AIN4(+)/REFIN2(+) REFIN1(+) AIN4()/REFIN2() REFIN1() DD REFERENCE V BIAS BAND GAP DETECT REFERENCE V DD GND AIN1(+) DOUT/RDY AIN1() SERIAL INTERFACE DIN - AIN2(+) BUF IN-AMP AND ADC SCLK AIN2() LOGIC CONTROL AIN3(+) CS MUX AIN3() AIN5(+)/IOUT2 GND AIN5()/IOUT1 AIN6(+)/P1 TEMP INTERNAL DV SENSOR CLOCK DD AIN6()/P2 V AD7794/AD7795 DD PSW AD7794: 24-BIT ADC AD7795: 16-BIT ADC GND CLK Figure 1. Rev. D 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 www.analog.com license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Fax: 781.461.3113 20042007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 04854-001AD7794/AD7795 TABLE OF CONTENTS Features .............................................................................................. 1 Full-Scale Register...................................................................... 25 Applications....................................................................................... 1 ADC Circuit Information.............................................................. 26 General Description ......................................................................... 1 Overview ..................................................................................... 26 Functional Block Diagram .............................................................. 1 Digital Interface.......................................................................... 28 Revision History ............................................................................... 2 Circuit Description......................................................................... 31 Specifications..................................................................................... 3 Analog Input Channel ............................................................... 31 Timing Characteristics..................................................................... 8 Instrumentation Amplifier........................................................ 31 Timing Diagrams.............................................................................. 9 Bipolar/Unipolar Configuration .............................................. 31 Absolute Maximum Ratings.......................................................... 10 Data Output Coding .................................................................. 32 ESD Caution................................................................................ 10 Burnout Currents ....................................................................... 32 Pin Configuration and Function Descriptions........................... 11 Excitation Currents .................................................................... 32 RMS Noise and Resolution Specifications .................................. 13 Bias Voltage Generator .............................................................. 32 Chop Enabled.............................................................................. 13 Reference ..................................................................................... 32 Chop Disabled ............................................................................ 15 Reference Detect......................................................................... 33 Typical Performance Characteristics ........................................... 16 Reset ............................................................................................. 33 On-Chip Registers.......................................................................... 17 AV Monitor ............................................................................. 33 DD Communications Register......................................................... 17 Calibration................................................................................... 33 Status Register............................................................................. 18 Grounding and Layout .............................................................. 34 Mode Register ............................................................................. 19 Applications Information .............................................................. 35 Configuration Register .............................................................. 22 Flowmeter.................................................................................... 35 Data Register ............................................................................... 24 Outline Dimensions ....................................................................... 36 ID Register................................................................................... 24 Ordering Guide .......................................................................... 36 IO Register................................................................................... 24 Offset Register............................................................................. 25 REVISION HISTORY 3/07Rev. C to Rev. D 4/05Rev. 0 to Rev. A Changes to Specifications Endnote 1............................................. 7 Changes to Absolute Maximum Ratings........................................9 Changes to Status Register Section .............................................. 18 Changes to Figure 21...................................................................... 25 Changes to Ordering Guide .......................................................... 36 Changes to Data Output Coding Section.................................... 28 Changes to Calibration Section .................................................... 30 10/06Rev. B to Rev. C Changes to Ordering Guide .......................................................... 33 Updated Format..................................................................Universal Added AD7794 C-Grade Part...........................................Universal 10/04Revision 0: Initial Version Changes to Specifications................................................................ 3 Changes to Ordering Guide .......................................................... 36 6/06Rev. A to Rev. B Added AD7795 ...................................................................Universal Changes to Features.......................................................................... 1 Changes to Table 1............................................................................ 3 Changes to RMS Noise and Resolution Specifications Section..................................................................... 12 Changes to Table 19........................................................................ 20 Changes to ADC Circuit Information Section ........................... 25 Changes to Ordering Guide .......................................................... 35 Rev. D Page 2 of 36