Datasheet

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
FAST Step 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.
a
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
REGISTER BANK
CLOCK
GENERATION
PROGRAMMABLE
DIGITAL
FILTER
SIGMA-DELTA A/D CONVERTER
BUFFER
PGA
100nA
AGND
100nA
AV
DD
VBIAS
AIN1(+)
AIN1(–)
AIN2(+)/D1
AIN2(–)/D0
ACX
ACX
STANDBY
SYNC
MCLK IN
MCLK OUT
SCLK
CS
DIN
DOUT
RESET
RDY
POL
DGNDAGND
AV
DD
DV
DD
REF IN(–)
REF IN(+)
MUX
REFERENCE DETECT
AC
EXCITATION
CLOCK
+
–
REV. B