AD7714
APPLICATIONS
arranged in a bridge network and gives a differential output
voltage between its OUT(+) and OUT(–) terminals. With rated
full-scale pressure (in this case 300 mmHg) on the transducer,
the differential output voltage is 3 mV/Volt of the input voltage
(i.e., the voltage between its IN(+) and IN(–) terminals).
Assuming a 5 V excitation voltage, the full-scale output range
from the transducer is 15 mV. The excitation voltage for the
bridge is also used to generate the reference voltage for the
AD7714. Therefore, variations in the excitation voltage do not
introduce errors in the system. Choosing resistor values of
24 kΩ and 15 kΩ as per the diagram give a 1.92 V reference
voltage for the AD7714 when the excitation voltage is 5 V.
Using the part with a programmed gain of 128 results in the full
scale input span of the AD7714 being 15 mV which corresponds
with the output span from the transducer.
The on-chip PGA allows the AD7714 to handle an analog input
voltage range as low as 10 mV full-scale with VREF = +1.25 V.
The differential inputs of the part allow this analog input range
to have an absolute value anywhere between AGND and AVDD
when the part is operated in unbuffered mode. It allows the user
to connect the transducer directly to the input of the AD7714.
The programmable gain front end on the AD7714 allows the
part to handle unipolar analog input ranges from 0 mV to
+20 mV to 0 V to +2.5 V and bipolar inputs of ±20 mV to
±2.5 V. Because the part operates from a single supply these
bipolar ranges are with respect to a biased-up differential input.
Pressure Measurement
One typical application of the AD7714 is pressure measure-
ment. Figure 12 shows the AD7714 used with a pressure trans-
ducer, the BP01 from Sensym. The pressure transducer is
+5V
EXCITATION VOLTAGE = +5V
DV
AV
DD
DD
AV
DD
IN+
IN–
AD7714
1A
AIN1
AIN2
OUT+
CHARGE BALANCING A/D
OUT–
STANDBY
CONVERTER
AUTO-ZEROED
DIGITAL
SYNC
AIN3
AIN4
AIN5
AIN6
⌺⌬
PGA
A = 1–128
FILTER
BUFFER
MODULATOR
24k⍀
MCLK IN
CLOCK
GENERATION
1A
SERIAL INTERFACE
REGISTER BANK
MCLK OUT
AGND
REF IN (+)
RESET
15k⍀
DRDY
POL
REF IN (–)
AGND
BUFFER
DGND
SCLK
DOUT
CS
DIN
Figure 12. Pressure Measurement Using the AD7714
–34–
REV. C
ADI [ ADI ]
