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APPLICATIONS Portable Industrial Instruments Portable Weigh Scales Loop-Powered Systems Pressure Transducers GENERAL DESCRIPTION†

The AD7714 is a complete analog front end for low-frequency measurement applications. The device accepts low level signals directly from a transducer and outputs a serial digital word. It employs a sigma-delta conversion technique to realize up to 24 bits of no missing codes performance. The input signal is applied to a proprietary programmable gain front end based around an analog modulator. The modulator output is processed by an onchip digital filter. The first notch of this digital filter can be programmed via the on-chip control register allowing adjustment of the filter cutoff and settling time. The part features three differential analog inputs (which can also be configured as five pseudo-differential analog inputs) as well as a differential reference input. It operates from a single supply (+3 V or +5 V). The AD7714 thus performs all signal conditioning and conversion for a system consisting of up to five channels. The AD7714 is ideal for use in smart, microcontroller- or DSPbased systems. It features a serial interface that can be configured *Protected by U.S. Patent No. 5,134,401. †See page 39 for data sheet index. SPI and QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor Corporation.

REV. C 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.

FUNCTIONAL BLOCK DIAGRAM AVDD DVDD REF IN(–) REF IN(+) AVDD

CHARGE BALANCING A/D CONVERTER

1␮A AIN1 AIN2 AIN3 AIN4 AIN5 AIN6

Σ -∆ MODULATOR

SWITCHING MATRIX

FEATURES Charge Balancing ADC 24 Bits No Missing Codes 0.0015% Nonlinearity Five-Channel Programmable Gain Front End Gains from 1 to 128 Can Be Configured as Three Fully Differential Inputs or Five Pseudo-Differential Inputs Three-Wire Serial Interface SPI™, QSPI™, MICROWIRE™ and DSP Compatible 3 V (AD7714-3) or 5 V (AD7714-5) Operation Low Noise (<150 nV rms) Low Current (350 ␮A typ) with Power-Down (5 ␮A typ) AD7714Y Grade: +2.7 V to 3.3 V or +4.75 V to +5.25 V Operation 0.0010% Linearity Error –40؇C to +105؇C Temperature Range Schmitt Trigger on SCLK and DIN Low Current (226 ␮A typ) with Power-Down (4 ␮A typ) Lower Power Dissipation than Standard AD7714 Available in 24-Lead TSSOP Package Low-Pass Filter with Programmable Filter Cutoffs Ability to Read/Write Calibration Coefficients

3 V/5 V, CMOS, 500 ␮A Signal Conditioning ADC AD7714*

BUFFER

PGA

STANDBY SYNC

DIGITAL FILTER

A = 1–128 1␮A

SERIAL INTERFACE REGISTER BANK

AGND

SCLK

BUFFER

CS

MCLK IN MCLK OUT

DIN

CLOCK GENERATION

DOUT

AD7714 AGND

DGND

POL

DRDY

RESET

for three-wire operation. Gain settings, signal polarity and channel selection can be configured in software using the serial port. The AD7714 provides self-calibration, system calibration and background calibration options and also allows the user to read and write the on-chip calibration registers. CMOS construction ensures very low power dissipation, and the power-down mode reduces the standby power consumption to 15 µW typ. The part is available in a 24-pin, 0.3 inch-wide, plastic dual-in-line package (DIP); a 24-lead small outline (SOIC) package, a 28-lead shrink small outline package (SSOP) and a 24-lead thin shrink small outline package (TSSOP). PRODUCT HIGHLIGHTS

1. The AD7714Y offers the following features in addition to the standard AD7714: wider temperature range, Schmitt trigger on SCLK and DIN, operation down to 2.7 V, lower power consumption, better linearity, and availability in 24-lead TSSOP package. 2. The AD7714 consumes less than 500 µA (fCLK IN = 1 MHz) or 1 mA (fCLK IN = 2.5 MHz) in total supply current, making it ideal for use in loopowered systems. 3. The programmable gain channels allow the AD7714 to accept input signals directly from a strain gage or transducer removing a considerable amount of signal conditioning. 4. The AD7714 is ideal for microcontroller or DSP processor applications with a three-wire serial interface reducing the number of interconnect lines and reducing the number of optocouplers required in isolated systems. The part contains on-chip registers that allow control over filter cutoff, input gain, channel selection, signal polarity and calibration modes. 5. The part features excellent static performance specifications with 24-bit no missing codes, ±0.0015% accuracy and low rms noise (140 nV). Endpoint errors and the effects of temperature drift are eliminated by on-chip self-calibration, which removes zero-scale and full-scale errors. 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


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