
AD7710
REV. F
–27–
APPLICATIONS
Figure 20 shows a strain gage interfaced directly to one of the
analog input channels of the AD7710. The differential inputs to
the AD7710 are connected directly to the bridge network of the
strain gage. In the diagram shown, the on-chip reference of the
AD7710 provides the voltage for the bridge network and also
provides the reference voltage for the AD7710. An alternative
scheme, outlined in Figure 21, shows the analog positive supply
voltage powering the bridge network and the AD7710 with the
CLOCK
GENERATION
SERIAL INTERFACE
CONTROL
REGISTER
OUTPUT
REGISTER
CHARGE-BALANCING A/D
CONVERTER
DIGITAL
FILTER
AD7710
M
U
X
PGA
AGND
DGND
MODE SDATA SCLK
A0
MCLK
OUT
MCLK
I
N
AIN1(+)
AIN1(–)
REF
IN (–)
REF
IN (+)
SYNC
A = 1 – 128
DRDY
TFS
RFS
AIN2(+)
AIN2(–)
V
SS
V
BIAS
AV
DD
DV
DD
2.5V
REFERENCE
REF
OUT
ANALOG
+5V SUPPLY
R
R
ACTIVE
GAGE
DUMMY
GAGE
AUTO-ZEROED
MODULATOR
Figure 20. Strain-Gage Application with the AD7710
CLOCK
GENERATION
SERIAL INTERFACE
CONTROL
REGISTER
OUTPUT
REGISTER
CHARGE-BALANCING A/D
CONVERTER
AUTO-ZEROED
MODULATOR
DIGITAL
FILTER
AD7710
M
U
X
PGA
AGND
DGND
MODE SDATA SCLK
A0
MCLK
OUT
MCLK
IN
AIN1(+)
AIN1(–)
SYNC
A = 1 – 128
DRDY
TFS
RFS
AIN2(+)
AIN2(–)
V
SS
V
BIAS
AV
DD
DV
DD
2.5V
REFERENCE
R
R
ACTIVE
GAGE
DUMMY
GAGE
DIGITAL
+5V SUPPLY
ANALOG SUPPLY
EXCITATION
CURRENT
REF IN(+)
R =
V
REF
I
EXCITATION
REF IN(–)
REF
OUT
Figure 21. Alternate Scheme for Generating AD7710 Reference Voltage
reference voltage for the AD7710 generated across a resistor
which is placed in series with the bridge network. In this case,
the value of the reference resistor is determined by the required
reference voltage divided by the value of the excitation current.
The on-chip PGA allows the AD7710 to handle an analog input
voltage range as low as 20 mV full scale. The differential inputs
of the part allow this analog input range to have an absolute
value anywhere between V
SS
and AV
DD
.