16-Bit - ADC with a Switchable Current Sources AD7709 FEATURES APPLICATIONS 16-Bit - ADC Sensor Measurement Programmable Gain Front End Temperature Measurement Simultaneous 50 Hz and 60 Hz Rejection at 20 Hz Pressure Measurements Update Rate Weigh Scales VREF Select Allows Absolute and Ratiometric Portable Instrumentation Measurement Capability 420 mA Loops ISOURCE Select GENERAL DESCRIPTION 16-Bit No Missing Codes The AD7709 is a complete analog front end for low frequency 13-Bit p-p Resolution 20 Hz, 20 mV Range measurement applications. It contains a 16-bit - ADC, selectable 16-Bit p-p Resolution 20 Hz, 2.56 V Range reference inputs, three switchable matched excitation current INTERFACE sources, low-side power switches, and a digital I/O port. The 3-Wire Serial 16-bit channel with PGA accepts fully differential, unipolar, SPI , QSPI, MICROWIRE, and DSP Compatible and bipolar input signal ranges from 1.024 REFIN/128 to Schmitt Trigger on SCLK 1.024 REFIN. It can be configured as two fully differential input channels or four pseudo-differential input channels. Signals POWER can be converted directly from a transducer without the need for Specified for Single 3 V and 5 V Operation signal conditioning. Normal: 1.25 mA Typ 3 V The device operates from a 32.768 kHz crystal with an on-chip Power-Down: 7 A (32.768 kHz Crystal Running) PLL generating the required internal operating frequency. The ON-CHIP FUNCTIONS output data rate from the part is software programmable. The Rail-to-Rail Input Buffer and PGA p-p resolution from the part varies with the programmed gain Selectable Reference Inputs and output data rate. 3 Switchable, Ratioed Current Sources for The part operates from a single 3 V or 5 V supply. When V Measurements BE operating from 3 V supplies, the power dissipation for the part 4-Bit Digital I/O Port is 3.75 mW. The AD7709 is housed in a 24-lead TSSOP package. Low-Side Power Switches FUNCTIONAL BLOCK DIAGRAM REFIN1(+) REFIN2(+) REFIN1() REFIN2() XTAL1 XTAL2 V DD IEXC1 IEXC2 IEXC3 OSCILLATOR 8I 8I I AND IOUT1 PLL DOUT DIN I = 25 A SERIAL IOUT2 INTERFACE SCLK AND AIN1 CS CONTROL AIN2 LOGIC RDY PGA 16-BIT - ADC BUF AIN3/P3 MUX V RESET DD AIN4/P4 AINCOM I/O PORT AD7709 V GND PWRGND P1/SW1 P2/SW2 DD REV. A 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 rights of third parties that One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. may result from its use. No license is granted by implication or otherwise Tel: 781/329-4700 www.analog.com under any patent or patent rights of Analog Devices. Trademarks and Fax: 781/326-8703 2003 Analog Devices, Inc. All rights reserved. registered trademarks are the property of their respective companies.AD7709 TABLE OF CONTENTS FEATURES . 1 MICROCOMPUTER/MICROPROCESSOR GENERAL DESCRIPTION . 1 INTERFACING . 20 FUNCTIONAL BLOCK DIAGRAM . 1 AD7709-to-68HC11 Interface . 21 SPECIFICATIONS . 3 AD7709-to-8051 Interface 21 TIMING CHARACTERISTICS . 6 AD7709-to-ADSP-2103/ADSP-2105 Interface 21 ABSOLUTE MAXIMUM RATINGS . 8 CIRCUIT DESCRIPTION 22 ORDERING GUIDE 8 Analog Input Channels 22 PIN CONFIGURATION . 8 Programmable Gain Amplifier . 23 PIN FUNCTION DESCRIPTIONS 9 Bipolar/Unipolar Configuration 23 TYPICAL PERFORMANCE CHARACTERISTICS 10 Data Output Coding 23 ADC CIRCUIT INFORMATION . 11 Excitation Currents . 24 Overview . 11 Crystal Oscillator . 24 S-D ADC . 11 Reference Input 24 NOISE PERFORMANCE . 13 Reset Input . 24 ON-CHIP REGISTERS . 13 Power-Down Mode . 24 Communications Register 14 Grounding and Layout . 24 Status Register . 15 APPLICATIONS 25 Configuration Register . 16 Pressure Measurement . 25 Filter Register . 18 Temperature Measurement . 26 ADC Data Result Register 18 3-Wire RTD Configurations 27 CONFIGURING THE AD7709 . 19 Smart Transmitters . 28 DIGITAL INTERFACE . 20 OUTLINE DIMENSIONS . 29 Revision History . 30 2 REV. A