Datasheet CN-0233 Datasheet (ANALOG DEVICES)

Circuit Note

Circuits from the Lab™ circuits from Analog Devices have been designed and built by Analog Devices

. Standard engineering practices have been employed in the design and construction of

each circuit, and their function and performance have been tested and verified in a lab environment at

suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices
be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause

T1: COILTRONICS KA4976- AL
1:5 TURNS RATI O

+5V

+5V

ISO ISO

15kΩ

0.1%
5ppm/°C

4nF

ISO

ISO

ISO

ISO

R2 90.9kΩ

0.1µF

R3

10.5kΩ

ISO

R1 24.9kΩ

–15V (AVSS)

+15V (AVDD)

R

OC

100kΩ

D1 TO D4: MBR0540

DV

CCAVDD

–V

SENSE

R

L

CURRENT

OUTPUT

VOLTAGE
OUTPUT

V

OUT

R

SET

C

COMP

AV

SS

LATCH
SCLK
SDIN
SDO

CLR GND CLR SEL

FAULT

REFIN

I

OUT

+V

SENSE

AVDD

ISO ISOISO

ISO ISO

ISO

V

IN

ADR445

AD5422

V

OUT

AVSS

V

FB

1.25V

ADuM3471

+

+

+

ISO

ISO

+

+5V

IN

47µF

1
2
3
4
5
6
7
8
9

10

20
19
18
17
16
15
14
13
12
11

47µF

10µF 0.1µF

10µF 0.1µF 10µF 0.1µF 0.1µF

10µF 0.1µF

47µF

0.1µF

47µH

47µH

L1

D11:5

T1

D2

D3

D4

X1

GND

1

VDD

1

X2
I/OA
I/OB
I/OC
I/OD

I/OA
I/OB
I/OC
I/OD

V

DDA

GND

1

GND

2

V

REG

GND

2

VDD

2

FB

OC

L2

10126-001

Circuits from the Lab™ reference circuits are engineered and
tested for quick and easy system integration to help solve today’s
analog, mixed-signal, and RF design challenges. For more
information and/or support, visit www.analog.com/CN0233.

16-Bit Isolated Industrial Voltage and Current Output DAC

with Isolated DC-to-DC Supplies

EVALUATION AND DESIGN SUPPORT

Design and Integration Files
Schematics, Layout Files, Bill of Materials

CIRCUIT FUNCTION AND BENEFITS

Industrial and instrumentation systems, as well as program­mable logic controllers (PLCs) and distributed control systems
(DCS), must often control outputs, which can be both current
controlled (4 mA to 20 mA), and voltage controlled (up to
±10 V). Typically, such designs also need to be isolated from the
local system controller to protect against ground loops and also

CN-0233

Devices Connected/Referenced

ADuM3471

AD5422

ADR445 Precision 5.0 V Reference

to ensure robustness against external events. Traditional solutions
use discrete ICs for both power and digital isolation.

When multichannel isolation is needed, the cost and space
of providing discrete solutions becomes a big disadvantage.
Solutions based on opto-isolators typically have reasonable
output regulation but require additional external components,
thereby increasing board area. Power modules are often bulky
and may provide poor output regulation. The circuit in Figure 1
is based on the ADuM347x family of isolators (ADuM3470,

ADuM3471, ADuM3472, ADuM3473, ADuM3474) and

Quad Isolator with Integrated
Transformer Driver and PWM Controller.

16-Bit Current Source and Voltage
Output DAC

Rev.0

engineers

room temperature. However, you are solely responsible for testing the circuit and determining its

whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page)

Figure 1. Isolated 16-Bit Current and Voltage Output DAC with Isolated Power Supplies.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]
Fax: [phone] ©2011

Analog Devices, Inc. All rights reserved.

www.analog.com

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

0 32,768 65,535

10126-002

INL (LS Bs)

CODE

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

0 32,768 65,535

10126-003

INL (LS Bs)

CODE

CN-0233 Circuit Note

integrates digital isolation, as well as the PWM-controlled
power regulation circuitry along with associated feedback
isolation. External transformers are used to transfer power
across the isolation barrier. The AD5422 16-bit DAC provides
the current and voltage outputs.

CIRCUIT DESCRIPTION

The AD5422 is a fully integrated, fully programmable 16-bit
voltage and current output DAC, capable of programming
ranges from 4 mA to 20 mA, 0 mA to 20 mA, 0 V to 5 V, 0 V to
10 V, ±5 V, ±10 V. The voltage output headroom is typically
1 V, and the current output needs about 2.5 V headroom.
This means that the 20 mA current output can drive a load of
approximately 600 Ω with a 15 V supply.

The ADuM347x devices are quad-channel digital isolators with
an integrated PWM controller and low impedance transformer
drivers (X1 and X2). The only additional components required
for an isolated dc-to-dc converter are a transformer and simple
full-wave diode rectifier. The devices provide up to 2 W of
regulated, isolated power when supplied from a 5.0 V or 3.3 V
input. This eliminates the need for a separate isolated dc-to-dc
converter.

The iCoupler chip-scale transformer technology is used to
isolate the logic signals, and the integrated transformer driver
with isolated secondary side control provides high efficiency
for the isolated dc-to-dc converter. The internal oscillator
frequency is adjustable from 200 kHz to 1 MHz and is
determined by the value of R
switching frequency is 500 kHz.

The ADuM3471 regulation is from the positive 15 V supply.
The feedback for regulation is from the divider network (R1,
R2, R3). The resistors are chosen such that the feedback voltage
is 1.25 V when the output voltage is 15 V. The feedback voltage
is compared with the ADuM3471 internal feedback setpoint
voltage of 1.25 V. Regulation is achieved by varying the duty
cycle of the PWM signals driving the external transformer.

The negative supply is loosely regulated and for light loads can
be as high as −23 V. This is within the maximum operating
value of −26.3 V. With nominal loads greater than 1 kΩ, the
additional power dissipation due to the larger unregulated
negative supply voltage is not a problem. In applications that
require higher compliance voltages or where very low power
dissipation is required, a different power supply design should
be considered.

This circuit was tested with the ADR445 5 V, high precision, low
drift (3 ppm/°C maximum for B grade) external reference. This
allows total system errors of less than 0.1% to be achieved over
the industrial temperature range (−40°C to +85°C).

. For ROC = 100 kΩ, the

OC

The AD5422 has a high precision integrated internal reference
with a drift of 10 ppm/°C maximum. If this reference is used
rather than the external reference, only 0.065% additional error
is incurred across the industrial temperature range.

The AD5422 integral nonlinearity (INL) was tested using both
linear supplies and the isolated dc-to-dc switching supplies to
ensure no loss in system accuracy was incurred because of the
switching supplies. Figure 2 shows the INL for the linear
supplies and Figure 3 for the switching supplies. There is no
noticeable performance loss when using the switching supply as
compared to the linear supply.

Figure 2. Measured INL of Circuit for ±10V Output Range Using

Linear Supplies .

Figure 3. Measured INL of Circuit for ± 10V Output Range Using

Switching Supplies .

Rev. 0 | Page 2 of 4

Circuit Note CN-0233

–5.0022

–5.0023

–5.0024

–5.0025

–5.0026

–5.0027

–5.0028

0 325

LINEAR SUPP LY

SWITCHING SUPPLY

650

10126-004

V

OUT

(V)

SAMPLES

ISO

+5V

+5V

ADuM3471

+15V

−15V

SPI SPI

EVAL-AD5422EBZ

(MODIFIED)

EVAL-ADuM3471EBZ

(MODIFIED)

AGILENT

E3630A

AGILENT

3458A

USB

USB

GPIB

ISO

AGILENT

E3630A

AD5422

USB

CONTROLLER

USB/GPIB

PC

ADR445

10126-005

The average output noise was also tested and compared over
time when using a linear supply and switching supply, as shown
in Figure 4. Note that there is a slight offset in output noise
measured over time. This offset can be attributed to a
combination of dc PSRR due to the difference in linear negative
supply versus the unregulated switching supply, as well as a
contribution due to the drift in the reference during the time
between the two measurements.

Figure 4. Measured Average DAC Output Noise for Linear and Switching

Supplies with DAC Output Set at −5 V on ±10 V Output Range

(1 LSB = 0.0003 V), 650 Samples.

COMMON VARIATIONS

This circuit is proven to work well with good stability and
accuracy with component values shown. Where the application
needs only the 4 mA to 20 mA current output, a single supply
scheme can be used. In this case, the positive AVCC supply can
be as large as 26.4 V and, therefore, the output compliance is

26.4 V – 2.5 V = 23.9 V. With an output current of 20 mA, a
load resistance as high as 1 kΩ is possible.

For applications not requiring 16-bit resolution, the 12-bit

AD5412 is available.

The ADuM347x isolators (ADuM3470, ADuM3471,

ADuM3472, ADuM3473, ADuM3474) provide four

independent isolation channels in a variety of input/output
channel configurations. These devices are also available with
either a maximum data rate of 1 Mbps (A grade) or 25 Mbps
(C grade).

CIRCUIT EVALUATION AND TEST

This circuit was tested using the E VAL-AD5422EBZ circuit
board and the EVA L-ADuM3471EBZ connected together as
shown in Figure 5. To ensure the isolation paths were tested
fully, the ground, power, and data tracks between the controller
and the AD5422 device were cut, and the signals were routed
through the ADuM3471 evaluation board.

Figure 5. Functional Block Diagram of Test Setup Showing Evaluation Board Connections

Rev. 0 | Page 3 of 4

CN-0233 Circuit Note

Equipment Used to Collect Test Data

• PC with a USB port and Windows® XP, Windows Vista®,

(32-bit), or Windows 7 (32-bit)

• E VAL-AD5422EBZ (modified)

• E VAL-ADuM3471EBZ (modified)

• Evaluation software for AD5422 board.

• Power supply: +5 V

• Power supply: ±15 V, Agilent E3630A or equivalent

• Agilent 3458A, 8.5 digit meter or equivalent

• National Instruments GPIB to USB-B interface and cable

Setup and Test

The circuit was tested and verified by connecting both the

ADuM3471 evaluation board and the AD5422 evaluation

board, as shown in Figure 5.

The double supply was set up as a positive and negative supply
on the ADuM3471 evaluation board by changing the trans­former to a 1:5 turns ratio transformer (Coilcraft KA4976-AL).
Other changes were removing the 0 Ω resistors from R24 and
R22 to R23 and R21. Short-circuiting R23 instead of R24 makes
the +7.5 V/6 V pin of J6 become the −15 V supply. Short­circuiting R21 instead of R22 connects the transformer center
tap to the ground plane instead of the node where L3, C20, and
C27 are connected.

Figure 16 of UG-197 shows which resistors should be short­circuited and open-circuited for the double supply or positive
and negative supply configurations. Note: See user guide

UG-197 for detailed information on these hardware changes.

The AD5422 evaluation board was modified to allow the digital
control signals to pass through the ADuM3471 evaluation
board. This allows the full data isolation path to the AD5422 to
be fully tested.

The INL and noise data were obtained by inputting the DAC
data to the AD5422 evaluation board from the PC and reading
the results from the 3485A meter using the GPIB/USB interface.
The AD5422 evaluation board software was used to generate
the data to the DAC.

LEARN MORE

CN-0233 Design Support Package:

http://www.analog.com/CN0233-DesignSupport

CN-0065 Circuit Note, 16-Bit Fully Isolated Output Module

Using the AD5422 Single Chip Voltage and Current Output
DAC and the ADuM1401 Digital Isolator, Analog Devices.

Cantrell, Mark. AN-0971 Application Note, Recommendations

for Control of Radiated Emissions with isoPower Devices.
Analog Devices.

Chen, Baoxing. 2006. iCoupler® Products with isoPower™

Technology: Signal and Power Transfer Across Isolation
Barrier Using Microtransformers. Analog Devices.

MT-014 Tutorial, Basic DAC Architectures I: String DACs and

Thermometer (Fully Decoded) DACs, Analog Devices.

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, RS-485,

and CAN Buses in Industrial, Instrumentation, and Computer
Applications. Analog Dialogue (October 2005).

Ardizzoni, John. A Practical Guide to High-Speed Printed-

Circuit-Board Layout, Analog Dialogue 39-09, September

2005.

MT-031 Tutorial, Grounding Data Converters and Solving the

Mystery of “AGND” and “DGND”, Analog Devices.

MT-101 Tutorial, Decoupling Techniques, Analog Devices.

Data Sheets and Evaluation Boards

AD5422 Data Sheet

AD5422 Evaluation Board (EVAL-AD5422EBZ)

ADuM3471 Data Sheet

ADuM3471 Evaluation Board (EVAL-ADuM3471EBZ)

UG-197 User Guide for ADuM3471 Evaluation Board

ADR445 Data Sheet

REVISION HISTORY

10/11—Rev. 0: Initial Version

(Continued from first page) Circuits from the L ab circuits are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you
may use the Circuits from the Lab circuits in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by
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purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices
reserves the right to change any Circuits from the Lab circuits at any time without notice but is under no obligation to do so.

©2011 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
CN10126-

0-10/11(0)

Rev. 0 | Page 4 of 4