AD7714YRZ-REEL Analog Devices Inc, AD7714YRZ-REEL Datasheet - Page 36

• Manufacturer Part Number: AD7714YRZ-REEL
• Description: 24-BIT SIGMA DELTA A/D IC
• Manufacturer: Analog Devices Inc

Specifications of AD7714YRZ-REEL

• Number Of Bits: 24
• Sampling Rate (per Second): 1k
• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 7mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (0.300", 7.50mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7714-3EBZ - BOARD EVALUATION FOR AD7714
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7714
RTD Measurement
Figure 14 shows another temperature measurement application
for the AD7714. In this case, the transducer is an RTD (Resis-
tive Temperature Device), a PT100. The arrangement is a 4-
lead RTD configuration. There are voltage drops across the lead
resistances R
mode voltage. There is no voltage drop across lead resistances
R
lead resistances present a small source impedance so it would
not generally be necessary to turn on the buffer on the AD7714.
L2
and R
L3
as the input current to the AD7714 is very low
L1
and R
RTD
L4
but these simply shift the common-
6.25k
R
R
R
L1
L3
L4
R
L2
REF IN (+)
REF IN (–)
400 A
DGND
AGND
AIN2
AIN1
Figure 14. RTD Measurement Using the AD7714
AGND
AV
+5V
AV
DD
DD
1 A
1 A
BUFFER
BUFFER DOUT
.
DV
SERIAL INTERFACE
The
DD
A = 1–128
PGA
–36–
If the buffer is required, the common-mode voltage should be
set accordingly by inserting a small resistance between the bot-
tom end of the RTD and AGND of the AD7714. In the appli-
cation shown an external 400 A current source provides the
excitation current for the PT100 and it also generates the refer-
ence voltage for the AD7714 via the 6.25 k resistor. Variations
in the excitation current do not affect the circuit as both the
input voltage and the reference voltage vary ratiometrically with
the excitation current. However, the 6.25 k resistor must have
a low temperature coefficient to avoid errors in the reference
voltage over temperature.
REGISTER BANK
AUTO-ZEROED
CHARGE BALANCING A/D
DIN
MODULATOR
CONVERTER
CS
GENERATION
AD7714
CLOCK
SCLK
DIGITAL
FILTER
MCLK IN
MCLK OUT
STANDBY
SYNC
RESET
DRDY
POL
REV. C