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AD7705 Datasheet(PDF) 1 Page - Analog Devices |
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AD7705 Datasheet(HTML) 1 Page - Analog Devices |
1 / 32 page 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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. a AD7705/AD7706 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 1998 3 V/5 V, 1 mW 2-/3-Channel 16-Bit, Sigma-Delta ADCs FUNCTIONAL BLOCK DIAGRAM FEATURES AD7705: Two Fully Differential Input Channel ADCs AD7706: Three Pseudo Differential Input Channel ADCs 16 Bits No Missing Codes 0.003% Nonlinearity Programmable Gain Front End Gains from 1 to 128 Three-Wire Serial Interface SPI™, QSPI™, MICROWIRE™ and DSP Compatible Schmitt Trigger Input on SCLK Ability to Buffer the Analog Input 2.7 V to 3.3 V or 4.75 V to 5.25 V Operation Power Dissipation 1 mW max @ 3 V Standby Current 8 A max 16-Lead DIP, 16-Lead SOIC and TSSOP Packages GENERAL DESCRIPTION The AD7705/AD7706 are complete analog front ends for low frequency measurement applications. These two-/three-channel devices can accept low level input signals directly from a trans- ducer and produce a serial digital output. They employ a sigma- delta conversion technique to realize up to 16 bits of no missing codes performance. The selected input signal is applied to a proprietary programmable gain front end based around an ana- log modulator. The modulator output is processed by an on- chip digital filter. The first notch of this digital filter can be programmed via an on-chip control register allowing adjustment of the filter cutoff and output update rate. The AD7705/AD7706 operate from a single 2.7 V to 3.3 V or 4.75 V to 5.25 V supply. The AD7705 features two fully differ- ential analog input channels while the AD7706 features three pseudo differential input channels. Both devices feature a differ- ential reference input. Input signal ranges of 0 mV to +20 mV through 0 V to +2.5 V can be incorporated on both devices when operating with a VDD of 5 V and a reference of 2.5 V. They can also handle bipolar input signal ranges of ±20 mV through ±2.5 V, which are referenced to the AIN(–) inputs on the AD7705 and to the COMMON input on the AD7706. The AD7705/AD7706, with 3 V supply and a 1.225 V reference, can handle unipolar input signal ranges of 0 mV to +10 mV through 0 V to +1.225 V. Its bipolar input signal ranges are ±10 mV through ±1.225 V. The AD7705/AD7706 thus perform all signal conditioning and conversion for a two- or three-channel system. The AD7705/AD7706 are ideal for use in smart, microcontroller or DSP-based systems. They feature a serial interface that can be configured for three-wire operation. Gain settings, signal polarity and update rate selection can be configured in software using the input serial port. The part contains self-calibration and system calibration options to eliminate gain and offset errors on the part itself or in the system. CMOS construction ensures very low power dissipation, and the power-down mode reduces the standby power consumption to 20 µW typ. These parts are available in a 16-lead, 0.3 inch-wide, plastic dual-in-line package (DIP), a 16-lead wide body (0.3 inch) small outline (SOIC) package and also a low profile 16- lead TSSOP. PRODUCT HIGHLIGHTS 1. The AD7705/AD7706 consumes less than 1 mW at 3 V supplies and 1 MHz master clock, making it ideal for use in low power systems. Standby current is less than 8 µA. 2. The programmable gain input allows the AD7705/AD7706 to accept input signals directly from a strain gage or trans- ducer, removing a considerable amount of signal conditioning. 3. The AD7705/AD7706 is ideal for microcontroller or DSP processor applications with a three-wire serial interface re- ducing the number of interconnect lines and reducing the number of opto-couplers required in isolated systems. 4. The part features excellent static performance specifications with 16 bits, no missing codes, ±0.003% accuracy and low rms noise (<600 nV). Endpoint errors and the effects of temperature drift are eliminated by on-chip calibration op- tions, which remove zero-scale and full-scale errors. * *Protected by U.S. Patent Number 5,134,401. SPI and QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor. VDD REF IN(–) REF IN(+) AD7705/AD7706 MAX PGA BUFFER CHARGE BALANCING A/D CONVERTER - MODULATOR DIGITAL FILTER A = 1 128 SERIAL INTERFACE REGISTER BANK CLOCK GENERATION MCLK IN MCLK OUT GND DRDY RESET DIN DOUT CS SCLK ANALOG INPUT CHANNELS |
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