a
Bridge Transducer ADC
AD7730/AD7730L
The modulator output is processed by a low pass programmable
digital filter, allowing adjustment of filter cutoff, output rate and
settling time.
KEY FEATURES
Resolution of 230,000 Counts (Peak-to-Peak)
Offset Drift: 5 nV/؇C
Gain Drift: 2 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
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. 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 230,000 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.
ADDITIONAL FEATURES
Two-Channel Programmable Gain Front End
On-Chip DAC for Offset/TARE Removal
FASTStep™ Mode
AC or DC Excitation
Single Supply Operation
The serial interface on the part can be configured for three-wire
operation and is compatible with microcontrollers and digital
signal processors. The AD7730 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 2 ppm/°C.
APPLICATIONS
Weigh Scales
Pressure Measurement
The AD7730 is available in a 24-pin plastic DIP, a 24-lead
SOIC and 24-lead TSSOP package. The AD7730L is available
in a 24-lead SOIC and 24-lead TSSOP package.
GENERAL DESCRIPTION
The AD7730 is a complete analog front end for weigh-scale and
pressure measurement applications. The device accepts lowlevel 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 modulator.
NOTE
The description of the functions and operation given in this data
sheet apply to both the AD7730 and AD7730L. Specifications
and performance parameters differ for the parts. Specifications
for the AD7730L are outlined in Appendix A.
FUNCTIONAL BLOCK DIAGRAM
AVDD
REF IN(–) REF IN(+)
DVDD
AD7730
REFERENCE DETECT
VBIAS
AVDD
AIN1(+)
SIGMA-DELTA A/D CONVERTER
BUFFER
100nA
AIN1(–)
+
MUX
+/–
SIGMADELTA
MODULATOR
PGA
PROGRAMMABLE
DIGITAL
FILTER
100nA
AIN2(+)/D1
AIN2(–)/D0
AGND
6-BIT
DAC
SERIAL INTERFACE
AND CONTROL LOGIC
CLOCK
GENERATION
REGISTER BANK
ACX
SYNC
MCLK IN
MCLK OUT
SCLK
CS
CALIBRATION
MICROCONTROLLER
ACX
STANDBY
DIN
AC
EXCITATION
CLOCK
DOUT
AGND
DGND
POL
RDY
RESET
FASTStep is a trademark of Analog Devices, Inc.
REV. B
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.
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: 781/461-3113
© Analog Devices, Inc., 2012
