CN-0065: 16-Bit Fully Isolated Output Module Using the AD5422 Single Chip...

Circuit Note
CN-0065
Devices Connected/Referenced
Circuit Designs Using Analog Devices Products
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AD5422
16-Bit VOUT/IOUT DAC
ADR445
Precision 5 V Reference
ADuM1401
Quad-Channel Digital Isolator
16-Bit Fully Isolated Output Module Using the AD5422 Single Chip Voltage and
Current Output DAC and the ADuM1401 Digital Isolator
CIRCUIT FUNCTION AND BENEFITS
CIRCUIT DESCRIPTION
This circuit provides a complete solution for an industrial
control output module. This design is suitable for process
control programmable logic controllers (PLCs) and distributed
control system (DCS) modules that require standard 4 mA-to20 mA current outputs and unipolar or bipolar output voltage
ranges. The AD5422 16-bit DAC is software configurable to
provide all necessary outputs and has many integrated
diagnostic features useful in an industrial environment. The
ADuM1401 provides all the necessary signal isolation between
the microcontroller and the DAC. The circuit also includes
standard external protection and has been tested and verified to
be fully compliant with IEC 61000 specifications.
For industrial control modules, standard analog output voltage
and current ranges include ±5 V, ±10 V, 0 V to 5 V, 0 V to 10 V,
4 mA to 20 mA, and 0 mA to 20 mA. The AD5422 is a precision,
fully integrated 16-bit DAC offering a programmable current
source and programmable voltage output designed to meet the
requirements of industrial process control applications.
The output current range of the circuit shown in Figure 1 is
programmable from 4 mA to 20 mA or 0 mA to 20 mA and has
an overrange function of 0 mA to 24 mA. Voltage output is
provided from a separate pin that can be configured to provide
0 V to 5 V, 0 V to 10 V, ±5 V, and ±10 V output ranges. An
overrange feature of 10% is available on all ranges. Analog
outputs are short- and open-circuit protected and can drive
capacitive loads of 1 μF and inductive loads of 1 H.
15V ISO
ADR445
0.1µF
VIN
VOUT
+ 10µF
0.1µF
ISO
ISO
BAS70-04LT1
+15V ISO
ISO
+15V ISO –15V ISO
+ 10µF 0.1µF
+5VISO
+ 10µF
0.1µF
NPN TRANSISTOR:
MMBT8099L
B
ISO
EXTERNAL INPUT
ADuM1401
3.3V
0.1µF
SYNC
SCLK
DIN
DOUT
3.3V
0V
VDD1
GND1
VIA
VIB
VIC
VOD
VE1
GND1
VDD2
GND2
VOA
VOB
VOC
VID
VE2
GND2
DIGITAL ISOLATOR
+ 10µF
ISO
1kΩ
0.1µF
0.1µF
ISO
AV
AVSS DVCC REFIN BOOST
DVCC DD
SELECT
IOUT
LATCH
+VSENSE
SCLK
AD5422
SDIN
VOUT
SDO
–VSENSE
CLEAR
FAULTCLEAR GND SELECT RSET CCOMP
22nF
C
20V TVS:
SMBJ20CA
E
10Ω
ISO
RL
TVS
20V
600Ω AT 100MHz
FERRITE BEAD
4nF ISO
ISO
–15V ISO
CURRENT
OUTPUT
ISO
ISO
VOLTAGE
OUTPUT
TVS
20V
ISO
+15VISO
–15V ISO
15kΩ, 0.1%
BAS70-04LT1
5ppm/°C
ISO
20V TVS:
SMBJ20CA
08347-001
+ 10µF
Figure 1. 16 -Bit Industrial Control Output Module, Integrated Diagnostics,
Output Protection (Simplified Schematic)
Rev. B
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CN-0065
Circuit Note
output voltage error in %FSR (full-scale range) across a nominal
0 V to 10 V output range.
0.020
0.015
OUTPUT ERROR (%FSR)
The ADuM1401 is a quad-channel digital isolator based on
Analog Devices, Inc., iCoupler® technology. It is used to provide
isolation between the AD5422 and the system microcontroller,
with an isolation rating of 2.5 kV rms. All four wires are used to
connect the standard SPI interface to the AD5422: three wires
transmit (LATCH, SCLK, and SDIN) and one wire receives (SDO).
The AD5422 has an on-board 10 ppm/°C reference. For high
performance over temperature, this design uses an external
ADR445 5 V reference. This device has 0.04% maximum
accuracy error and a 3 ppm/°C maximum temperature drift.
This drift contributes approximately 0.02% error across the
industrial temperature range.
0.010
0.005
0
–0.005
–0.010
–0.015
–0.020
08347-002
By default, the DVCC pin on the AD5422 accepts a power supply
of 2.7 V to 5.5 V. Alternatively, the DVCC SELECT pin can be
used to connect an internal 4.5 V power supply to the DVCC pin
for use as a digital power supply for other devices in the system
or as a termination for pull-up resistors. Maximum current
available from the DVCC pin in this mode is 5 mA. In this
design, the DVCC output is used to supply the field side of the
ADuM1401 digital isolator.
CODE
Figure 2. INL Accuracy Plot for a 0 V to 10 V Output Range
Figure 2 shows a plot of the output error of the AD5422 when
used with the ADR435 external reference. The data is shown as
This circuit is from a portion of the PLC demo system. The PLC
demo system has been successfully tested to the IEC 61000
standards shown in Table 1 (see Colm Slattery, Derrick
Hartmann, and Li Ke, “PLC Evaluation Board Simplifies Design
of Industrial Process Control Systems,” Analog Dialogue (April
2009) for more discussion of external protection techniques.
Table 1. Conformance to IEC Specifications 1
Test Item
EN55022
EN and IEC 61000-4-2
EN and IEC 61000-4-3
EN and IEC 61000-4-4
EN and IEC 61000-4-5
EN and IEC 61000-4-6
1
Description
Radiated emission Class A,
3 meter anechoic chamber
Electrostatic discharge (ESD)
±8 kV VCD
Electrostatic discharge (ESD)
±8 kV HCD
Radiated immunity 80 MHz to
1 GHz 18 V/m, vertical antenna
polarization
Radiated immunity 80 MHz to
1 GHz 18 V/m, horizontal antenna
polarization
Electrically fast transient (EFT)
±4 kV power port
Electrically fast transient (EFT)
±2 kV analog I/O ports
Power line surge, ±2 kV
Immunity test on power cord,
10 V/m for 30 minutes
Immunity test on I/O cable,
10 V/m for 30 minutes
Result
Passed and met −6 dB margin.
Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4
are respectively −8 ppm, 10 ppm, and 13 ppm when there is interference.
Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4
are respectively −8 ppm, 10 ppm, and 13 ppm when there is interference.
Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4
are respectively 0.05%, 0.004%, and −0.13%. Performance automatically
resorted to ≤0.05% after interference. Class B.
Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4
are respectively −0.09%, 0.003%, and −0.02%. Performance automatically
resorted to ≤0.05% after interference. Class B.
Passed Class B.
Passed Class B.
No board or part damage occurred, no performance degrade, passed with
Class A.
Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4
are respectively 9.3%, 11%, and 3.4%. Passed Class B.
Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4
are respectively 4.5%, 4.7%, and 1.4%. Performance automatically resorted to
≤0.05% when interference stopped.
A sample was tested during initial release of the PLC Demo system (V07) and met the test compliances listed in this table. These results should be viewed as typical
data taken at 25°C. For these tests, the DAC outputs were connected to the ADC inputs, that is, DAC_CH2 to ADC_CH2, DAC_CH3 to ADC_CH3, and DAC_CH4 to
ADC_CH4. The DAC outputs were set to 5 V, 6 V, and 10 mA, respectively. The ADC channels correspond to the circuit as in CN0067.
Rev. B | Page 2 of 3
Circuit Note
CN-0065
LEARN MORE
Data Sheets and Evaluation Boards
Cantrell, Mark. AN-0971 Application Note, Recommendations
for Control of Radiated Emissions with isoPower Devices.
Analog Devices.
PLC Demo System.
Chen, Baoxing. 2006. iCoupler® Products with isoPower™
Technology: Signal and Power Transfer Across Isolation
Barrier Using Microtransformers. Analog Devices.
ADuM1401 Evaluation Board.
AD5422 Data Sheet.
ADR445 Data Sheet.
ADuM1401 Data Sheet.
MT-014 Tutorial, Basic DAC Architectures I: String DACs and
Thermometer (Fully Decoded) DACs, Analog Devices.
REVISION HISTORY
5/11—Rev. A to Rev. B
MT-015 Tutorial, Basic DAC Architectures II: Binary DACs,
Analog Devices.
MT-016 Tutorial, Basic DAC Architectures III: Segmented DACs,
Analog Devices.
Slattery, Colm, Derrick Hartmann, and Li Ke. “PLC Evaluation
Board Simplifies Design of Industrial Process Control
Systems.” Analog Dialogue (April 2009).
Wayne, Scott. “iCoupler® Digital Isolators Protect RS-232, RS485, and CAN Buses in Industrial, Instrumentation, and
Computer Applications.” Analog Dialogue (October 2005).
Changes to Circuit Function and Benefits Section....................... 1
Changes to Figure 1 .......................................................................... 1
Changes to Circuit Description Section......................................... 2
Changes to Table 1 ............................................................................ 2
Changes to Learn More Section ...................................................... 3
8/09—Rev. 0 to Rev. A
Updated Figure 1 ............................................................................... 1
7/09—Revision 0: Initial Version
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CN08347-0-5/11(B)
Rev. B | Page 3 of 3
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