AN-1241: Simplified 16-Bit Voltage Output and 4 mA-to-20 mA Output Solution Using the AD5422 (Rev. A) PDF

AN-1241
APPLICATION NOTE
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Simplified 16-Bit Voltage Output and 4 mA-to-20 mA Output Solution
Using the AD5422
CIRCUIT FUNCTION AND BENEFITS
CIRCUIT DESCRIPTION
This circuit provides unipolar/bipolar voltage and 4 mA-to20 mA outputs using the AD5422, a single channel, 16-bit,
serial input, unipolar/bipolar voltage, 4 mA-to-20 mA current
source DAC. This circuit utilizes only the AD5422 product. The
only external components needed are decoupling capacitors on the
supply pins and reference input and a pull-up resistor for the opendrain FAULT output, which alerts to a loss of compliance voltage
on the current output or an overtemperature of the AD5422. This
solution offers a level of integration that leads to savings in both
cost and board space. This circuit is well suited for both
programmable logic controllers (PLCs) and distributed control
systems (DCSes) in industrial control applications.
The AD5422 is a low cost, precision, highly integrated, 16-bit
digital-to-analog converter offering a programmable current
source and a programmable voltage output designed to meet
the requirements of industrial process control applications. The
voltage output range can be programmed at 0 V to +5 V, 0 V to
+10 V, −5 V to +5 V, or −10 V to +10 V. The current output,
which is accessed from a separate pin, can be programmed with
the ranges of 4 mA to 20 mA, 0 mA to 20 mA, or 0 mA to 24 mA.
The AD5422 contains an internal 5 V, 10 ppm/°C maximum
voltage reference. This leads to further savings in both cost and
board space. Operation is specified with an AVDD supply up to
24 V and an AVSS supply up to −24 V. However, the AD5422 is
capable of operating with an AVDD supply of up to 40 V. The
AD5422 contains an on-chip regulated 4.5 V output (DVCC pin)
capable of sourcing up to 5 mA. This can be used as a termination
for pull-up resistors or to power digital circuitry, thereby
eliminating the need to generate a logic power supply voltage.
+
+15V
0.1µF
10µF
0.1µF
CCOMP
AVDD
DVCC DVCC
SELECT
+VSENSE
CLEAR
SELECT
AD5422
VOUT
CLEAR
–VSENSE
LATCH
SCLK
BOOST
SDIN
IOUT
FAULT
SDO
GND AVSS REFOUT REFIN RSET
VOUT
IOUT
0.1µF
+
10µF
0.1µF
–15V
Figure 1. Basic Connections of the AD5422
(Simplified Schematic)
Rev. A | Page 1 of 2
08285-001
CONTROLLER
10kΩ
AN-1241
Application Note
Figure 2 and Figure 3 show that the typical accuracy of this
circuit at 25°C ambient temperature is 0.016% for current
output and 0.012% for voltage output.
LEARN MORE
The circuit must be constructed on a multilayer PC board with
a large area ground plane. Proper layout, grounding, and
decoupling techniques must be used to achieve optimum
performance (see Tutorial MT-031, Grounding Data Converters
and Solving the Mystery of "AGND" and "DGND" and Tutorial
MT-101, Decoupling Techniques).
MT-015 Tutorial, Basic DAC Architectures II: Binary DACs.
Analog Devices.
Kester, Walt. 2005. The Data Conversion Handbook. Analog
Devices. Chapters 3 and 7.
MT-031 Tutorial, Grounding Data Converters and Solving the
Mystery of AGND and DGND. Analog Devices.
MT-101 Tutorial, Decoupling Techniques. Analog Devices.
Voltage Reference Wizard Design Tool.
0.020
AD5422 Data Sheet.
AD5422 Evaluation Board.
0.010
0.005
REVISION HISTORY
0
4/13—Rev. 0 to Rev. A
–0.005
Changed Document Title from CN-0077 to
AN-1241 .............................................................................. Universal
–0.010
TA = 25°C
RLOAD = 250Ω
7/09—Revision 0: Initial Version
60k
08285-002
–0.015
60k
08285-003
CURRENT OUTPUT ERROR (%FSR)
Data Sheets
4mA TO 20mA
0mA TO 20mA
0mA TO 24mA
0.015
–0.020
0
10k
20k
30k
40k
50k
DAC CODE
Figure 2. Current Output Accuracy
0.005
VOLTAGE OUTPUT ERROR (%FSR)
0.003
TA = 25°C
0.001
–0.001
–0.003
–0.005
–0.007
–0.009
0V TO +5V
0V TO +10V
–5V TO +5V
–10V TO +10V
–0.011
–0.013
–0.015
0
10k
20k
30k
40k
50k
DAC CODE
Figure 3. Voltage Output Accuracy
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AN08285-0-4/13(A)
Rev. A | Page 2 of 2
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