AD7714 Analog Devices Data Handbook/Manual

3 V/5 V, CMOS, 500 m A Signal Conditioning ADC AD7714* FUNCTIONAL BLOCK DIAGRAMFEATURES

Charge Balancing ADC

DVDDAVDD REF IN(–) REF IN(+)

24 Bits No Missing Codes 0.0015% Nonlinearity

AVDD CHARGE

Five-Channel Programmable Gain Front End BALANCING

1m A A/D CONVERTER

Gains from 1 to 128 STANDBY

AIN1 -∆

Can Be Configured as Three Fully Differential MODULATOR

Inputs or Five Pseudo-Differential Inputs AIN3

BUFFER PGA DIGITAL FILTER

Three-Wire Serial Interface AIN5

AIN6 A = 1–128

SPI™, QSPI™, MICROWIRE™ and DSP Compatible

3 V (AD7714-3) or 5 V (AD7714-5) Operation 1m A SERIAL INTERFACE

Low Noise (<150 n V rms) AGND REGISTER BANK SCLK

Low Current (350␣ m A typ) with Power-Down (5 m A typ) BUFFER CS

AD7714Y Grade: MCLK IN

CLOCK DIN

+2.7 V to 3.3 V or +4.75 V to +5.25 V Operation MCLK OUT GENERATION

0.0010% Linearity Error

AD7714

–408C to +1058C Temperature Range Schmitt Trigger on SCLK and DIN AGND DGND POL DRDY RESET Low Current (226␣ m A typ) with Power-Down (4 m A typ) for three-wire operation. Gain settings, signal polarity and channel Lower Power Dissipation than Standard AD7714 selection can be configured in software using the serial port. The Available in 24-Lead TSSOP Package AD7714 provides self-calibration, system calibration and back- Low-Pass Filter with Programmable Filter Cutoffs ground calibration options and also allows the user to read and

IT IN

Ability to Read/Write Calibration Coefficients write the on-chip calibration registers.

APPLICATIONS CMOS construction ensures very low power dissipation, and the Portable Industrial Instruments www.BDTIC.com/ADI power-down mode reduces the standby power consumption to Portable Weigh Scales 15␣ µW typ. The part is available in a 24-pin, 0.3 inch-wide, plastic Loop-Powered Systems dual-in-line package (DIP); a 24-lead small outline (SOIC) Pressure Transducers package, a 28-lead shrink small outline package (SSOP) and a

24-lead thin shrink small outline package (TSSOP).

GENERAL DESCRIPTION† The AD7714 is a complete analog front end for low-frequency PRODUCT HIGHLIGHTS measurement applications. The device accepts low level signals 1. The AD7714Y offers the following features in addition to the directly from a transducer and outputs a serial digital word. It standard AD7714: wider temperature range, Schmitt trigger employs a sigma-delta conversion technique to realize up to 24 on SCLK and DIN, operation down to 2.7 V, lower power bits of no missing codes performance. The input signal is applied consumption, better linearity, and availability in 24-lead to a proprietary programmable gain front end based around an TSSOP package. analog modulator. The modulator output is processed by an on-

2. The AD7714 consumes less than 500 µA (f CLK IN = 1␣ MHz)

chip digital filter. The first notch of this digital filter can be

or 1 m A (f CLK IN = 2.5␣ MHz) in total supply current, making

programmed via the on-chip control register allowing adjust-

it ideal for use in loop-powered systems.

ment of the filter cutoff and settling time.

3. The programmable gain channels allow the AD7714 to ac-

The part features three differential analog inputs (which can also cept input signals directly from a strain gage or transducer be configured as five pseudo-differential analog inputs) as well as a removing a considerable amount of signal conditioning. differential reference input. It operates from a single supply (+3␣

4. The AD7714 is ideal for microcontroller or DSP processor

or +5␣ V). The AD7714 thus performs all signal conditioning and

applications with a three-wire serial interface reducing the num-

conversion for a system consisting of up to five channels.

ber of interconnect lines and reducing the number of opto-

The AD7714 is ideal for use in smart, microcontroller- or DSP- couplers required in isolated systems. The part contains based systems. It features a serial interface that can be configured on-chip registers that allow control over filter cutoff, input gain,

*Protected by U.S. Patent No. 5,134,401. channel selection, signal polarity and calibration modes.

†See page 39 for data sheet index.

5. The part features excellent static performance specifications

SPI and QSPI are trademarks of Motorola, Inc.

with 24-bit no missing codes, ±0.0015% accuracy and low

MICROWIRE is a trademark of National Semiconductor Corporation.

rms noise (140 n V). Endpoint errors and the effects of tem-

REV. C

perature drift are eliminated by on-chip self-calibration, Information furnished by Analog Devices is believed to be accurate and which removes zero-scale and full-scale errors.

reliable. However, no responsibility is assumed by Analog Devices for its

use, nor for any infringements of patents or other rights of third parties One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. which may result from its use. No license is granted by implication or Tel: 781/329-4700 World Wide Web Site: http://www.analog.com

otherwise under any patent or patent rights of Analog Devices. Fax: 781/326-8703 © Analog Devices, Inc., 1998