AD7730LBR datasheet(44/53 Pages) AD

44 / 53 page

LOW POWER

BRIDGE TRANSDUCER ADC

KEY FEATURES

Resolution of 110,000 Counts (Peak-to-Peak)

Power Consumption: 15 mW typ

Offset Drift: < 1 ppm/ C

Gain Drift: 3 ppm/ C

Line Frequency Rejection: >150 dB

Buffered Differential Inputs

Programmable Filter Cutoffs

Specified for Drift Over Time

Operates with Reference Voltages of 1 V to 5 V

ADDITIONAL FEATURES

Two-Channel Programmable Gain Front End

On-Chip DAC for Offset/TARE Removal

FASTStep Mode

AC or DC Excitation

Single Supply Operation

APPLICATIONS

Portable Weigh Scales

FUNCTIONAL BLOCK DIAGRAM

Protected by U.S. Patent No: 5, 134, 401. Other Patent Applications Filed.

APPENDIX–AD7730L*

–44–

GENERAL DESCRIPTION

The AD7730L is a complete low power analog front-end for

weigh-scale and pressure measurement applications. The device

accepts low level signals directly from a transducer and outputs

a serial digital word. The input signal is applied to a proprietary

programmable gain front end based around an analog modula-

tor. The modulator output is processed by a low pass program-

mable digital filter, allowing adjustment of filter cutoff, output

rate and settling-time.

The part features two buffered differential programmable gain

analog inputs as well as a differential reference input. The part

operates from a single +5 V supply and typically consumes less

than 3 mA. It accepts four unipolar analog input ranges: 0 mV

to +10 mV, +20 mV, +40 mV and +80 mV and four bipolar

ranges

±10 mV, ±20 mV, ±40 mV and ±80 mV. The peak-to-

peak resolution achievable directly from the part is 1 in 110,000

counts. An on-chip 6-bit DAC allows the removal of TARE

voltages. Clock signals for synchronizing ac excitation of the

bridge are also provided.

The serial interface on the part can be configured for three-wire

operation and is compatible with microcontrollers and digital

signal processors. The AD7730L contains self-calibration and

system calibration options and features an offset drift of less

than 5 nV/

°C and a gain drift of less than 3 ppm/°C.

The part is available in a 24-lead SOIC and 24-lead TSSOP

package.

SIGMA-

DELTA

MODULATOR

AD7730L

6-BIT

DAC

SERIAL INTERFACE

AND CONTROL LOGIC

CLOCK

GENERATION

PROGRAMMABLE

DIGITAL

FILTER

SIGMA-DELTA A/D CONVERTER

BUFFER

PGA

100nA

AGND

100nA

AVDD

VBIAS

AIN1(+)

AIN1(–)

AIN2(+)/D1

AIN2(–)/D0

ACX

STANDBY

SYNC

MCLK IN

MCLK OUT

SCLK

DIN

DOUT

RESET

RDY

POL

DGND

AGND

AVDD

DVDD

REF IN(–) REF IN(+)

MUX

REFERENCE DETECT

EXCITATION

CLOCK

–

REV. B

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