AD7715ANZ-3 Analog Devices Inc, AD7715ANZ-3 Datasheet - Page 28

• Manufacturer Part Number: AD7715ANZ-3
• Description: IC ADC 16BIT SIGMA-DELTA 16DIP
• Manufacturer: Analog Devices Inc

Specifications of AD7715ANZ-3

• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Bits: 16
• Sampling Rate (per Second): 500
• Number Of Converters: 1
• Power Dissipation (max): 9.5mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 16-DIP (0.300", 7.62mm)
• Resolution (bits): 16bit
• Input Channel Type: Differential
• Supply Voltage Range - Analogue: 3V To 3.6V
• Supply Voltage Range - Digital: 3V To 5.25V
• Supply Current: 600µA
• No. Of: RoHS Compliant
• Sampling Rate: 19.2kSPS
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7715-3EBZ - BOARD EVALUATION FOR AD7715
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7715
Temperature Measurement
Another application area for the AD7715 is in temperature
measurement. Figure 13 outlines a connection from a thermo-
couple to the AD7715. In this application, the AD7715 is oper-
ated in its buffered mode to allow large decoupling capacitors
on the front end to eliminate any noise pickup which there may
have been in the thermocouple leads. When the AD7715 is
operated in buffered mode, it has a reduced common-mode
range. In order to place the differential voltage from the thermo-
couple on a suitable common-mode voltage, the AIN(–) input of
the AD7715 is biased up at the reference voltage, +2.5 V.
Figure 14 shows another temperature measurement application
for the AD7715. 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
THERMOCOUPLE
JUNCTION
GND
+V
RTD
REF192
IN
+5V
V
R
R
R
R
OUT
L3
L4
L1
L2
6.25k
400 A
Figure 13. Thermocouple Measurement Using the AD7715
R
R
REF IN (+)
REF IN (–)
DGND
AGND
Figure 14. RTD Measurement Using the AD7715
C
AIN(+)
AIN(–)
REF IN (–)
REF IN (+)
AIN (–)
AIN (+)
AGND
C
+5V
BUFFER
AV
DD
+5V
BUFFER
AV
DGND
DD
A = 1–128
PGA
DV
SERIAL INTERFACE
A = 1–128
DD
–28–
PGA
DV
DOUT
SERIAL INTERFACE
DD
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 AD7715.
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 AD7715. 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 AD7715 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.
DOUT
L2
AUTO-ZEROED
CHARGE BALANCING A/D
MODULATOR
and R
REGISTER BANK
DIN
AUTO-ZEROED
CHARGE BALANCING A/D
MODULATOR
CONVERTER
AD7715
REGISTER BANK
DIN
L3
CONVERTER
AD7715
as the input current to the AD7715 is very low
L1
CS
GENERATION
and R
DIGITAL
FILTER
CS
CLOCK
GENERATION
DIGITAL
SCLK
FILTER
L4
CLOCK
, but these simply shift the common-
SCLK
MCLK IN
MCLK OUT
RESET
DRDY
MCLK IN
MCLK OUT
RESET
DRDY
REV. C
.
The