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AD421BNZ

P1-P3P4-P6P7-P9P10-P12P13-P15
FUNCTIONAL BLOCK DIAGRAM
LOCAL
OSCILLATOR
SWITCHED
CURRENT
SOURCES
AND
FILTERING
BANDGAP
REFERENCE
REF IN
(+2.5V)
REF OUT1
(+1.25V)
REF OUT2
(+2.5V)
LV
V
CC
DRIVE
COMP
BOOST
LOOP
RTN
C1 C2 C3COM
LATCH
CLOCK
DATA
40⍀
16-BIT
SIGMA-
DELTA DAC
75k⍀
112.5k⍀
134k⍀
121k⍀
80k⍀
AD421
INPUT SHIFT
REGISTER
DAC LATCH
POWER-ON
RESET
REV. C
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
a
FEATURES
4 mA to 20 mA Current Output
HART
®
Compatible
16-Bit Resolution and Monotonicity
ⴞ0.01% Integral Nonlinearity
5 V or 3 V Regulator Output
2.5 V and 1.25 V Precision Reference
750 ␮A Quiescent Current max
Programmable Alarm Current Capability
Flexible High Speed Serial Interface
16-Lead SOIC and PDIP Packages
Loop-Powered
4 mA to 20 mA DAC
AD421
PRODUCT HIGHLIGHTS
1. The AD421 is a single chip, high performance, low cost
solution for generating 4 mA to 20 mA signals for smart
industrial control transmitters.
2. The AD421’s regulated supply voltage can be used to power
any additional circuits in the transmitter. The regulated
output value is pin selectable as either +3 V, +3.3 V or +5 V.
3. The AD421’s on-chip references can provide a precision
reference voltage to other devices in the system. This refer-
ence voltage can be either +1.25 V or +2.5 V.
4. The AD421 is fully compatible with standard HART cir-
cuitry or other similar FSK protocols.
5. With the addition of a single discrete transistor, the AD421
can be operated from V
CC
+ 2 V min to a maximum of the
breakdown voltage of the pass transistor.
6. The AD421 converts the digital data to current with 16-bit
resolution and monotonicity. Full-scale settling time to
± 0.1% typically occurs within 8 ms.
7. The AD421 features a programmable alarm current capabil-
ity that allows the transmitter to send out of range currents to
indicate a transducer fault.
HART is a registered trademark of the HART Communication
Foundation.
GENERAL DESCRIPTION
The AD421 is a complete, loop-powered, digital to 4 mA to
20 mA converter, designed to meet the needs of smart trans-
mitter manufacturers in the Industrial Control industry. It pro-
vides a high precision, fully integrated, low cost solution in a
compact 16-lead package. The AD421 is ideal for extending the
resolution of smart 4 mA to 20 mA transmitters at very low cost.
The AD421 includes a selectable regulator that is used to power
itself and other devices in the transmitter. This regulator pro-
vides either a +5 V, +3.3 V or +3 V regulated output voltage.
The part also contains +1.25 V and +2.5 V precision references.
The AD421 thus eliminates the need for a discrete regulator
and voltage reference. The only external components required
are a number of passive components and a pass transistor to
span large loop voltages.
The AD421 can be used with standard HART FSK protocol
communication circuitry without any degradation in specified
performance. The high speed serial interface is capable of oper-
ating at 10 Mbps and allows for simple connection to com-
monly-used microprocessors and microcontrollers via a standard
three-wire serial interface.
The sigma-delta architecture of the DAC guarantees 16-bit
monotonicity while the integral nonlinearity for the AD421 is
± 0.01%. The part provides a zero scale 4 mA output current
with ± 0.1% offset error and a 20 mA full-scale output current
with ± 0.2% gain error.
The AD421 is available in a 16-lead, 0.3 inch-wide, plastic DIP
and in a 16-lead, 0.3 inch-wide, SOIC package. The part is speci-
fied over the industrial temperature range of –40°C to +85°C.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 2000
AD421* PRODUCT PAGE QUICK LINKS
Last Content Update: 02/23/2017
COMPARABLE PARTS
View a parametric search of comparable parts.
DOCUMENTATION
Application Notes
• AN-534: Adding HART® Capability to the AD421, Loop-
Powered 4 mA–20 mA DAC Using the 20C15 HART
Modem
Data Sheet
• AD421: Loop-Powered 4-20 mA DAC Data Sheet
REFERENCE MATERIALS
Solutions Bulletins & Brochures
• Digital to Analog Converters ICs Solutions Bulletin
DESIGN RESOURCES
• AD421 Material Declaration
• PCN-PDN Information
• Quality And Reliability
• Symbols and Footprints
DISCUSSIONS
View all AD421 EngineerZone Discussions.
SAMPLE AND BUY
Visit the product page to see pricing options.
TECHNICAL SUPPORT
Submit a technical question or find your regional support
number.
DOCUMENT FEEDBACK
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DAC SPECIFICATIONS
Parameter B Versions
2
Units Conditions/Comments
ACCURACY
Resolution 16 Bits
Monotonicity 16 Bits min
Integral Nonlinearity ± 0.01 % of FS max FS = Full-Scale Output Current
Offset (4 mA) @ +25°C
4
± 0.1 % of FS max V
CC
= 5 V
Offset Drift ± 25 ppm of FS/°C max Includes On-Chip Reference Drift
Total Output Error (20 mA) @ +25°C
4
± 0.2 % of FS max V
CC
= 5 V
Total Output Drift ± 50 ppm of FS/°C max Includes On-Chip Reference Drift
V
CC
Supply Sensitivity 50 nA/mV max 25 nA/mV Typical
VOLTAGE REFERENCE
REF OUT2
Output Voltage 2.49/2.51 V min/V max 2.5 V Nominal
Drift ± 40 ppm/°C max 20 ppm/°C Typical from –40°C to +25°C and
–2.5 ppm/°C Typical from +25°C to +85°C
Externally Available Current 0.5 mA min
V
CC
Supply Sensitivity 150 µV/V max 15 µV/V Typical
Output Impedance 3 Ω typ
Noise (0.1 Hz–10 Hz) 6 µV (p-p) typ
REF OUT1
Output Voltage 1.24/1.26 V min/V max 1.25 V Nominal, 100 kΩ Load to COM
5
Drift ± 50 ppm/°C max 20 ppm/°C Typical from –40°C to +25°C and
2 ppm/°C Typical from +25°C to +85°C
Externally Available Current 0.5 mA min
V
CC
Supply Sensitivity 150 µV/V max 15 µV/V Typical
Output Impedance 3 Ω typ
Noise (0.1 Hz–10 Hz) 4 µV (p-p) typ
REF IN
Input Resistance 40 kΩ typ
DIGITAL INPUTS
V
IH
(Logic 1) 0.75 × V
CC
V min
V
IL
(Logic 0) 0.25 × V
CC
V max
I
IH
± 10 µA max V
IN
= V
CC
I
IL
± 10 µA max V
IN
= 0 V
Data Coding Binary
Data Rate 10 Mbps max
POWER SUPPLIES
Operating Range +2.95 to +5.05 V min to V max Functional to 7 V
Quiescent Current
@ V
CC
= 3 V 650 µA max 475 µA Typical
@ V
CC
= 5 V 750 µA max 575 µA Typical
NOTES
1
The DN25D is available from Supertex, Inc., 1350 Bordeaux Drive, Sunnyvale, CA 94089.
2
Temperature range is –40°C to +85°C.
3
The max current loop voltage compliance is determined by the pass transistor breakdown voltage and is 350 V for the DN25D.
4
With V
CC
= 3 V, the transfer function shifts negative by typically 0.25%; a 16 kΩ resistor connected between COM and LOOPRTN will approximately compensate for the V
CC
supply sensitivity in moving from 5 V to 3 V by skewing the gain of the AD421.
5
100 kΩ resistor only required if this reference is being used in application circuits.
Specifications subject to change without notice.
AD421–LOOP-POWERED SPECIFICATIONS
Parameter B Versions
2
Units Conditions/Comments
OUTPUT CHARACTERISTICS
Current Loop Voltage Compliance
3
V
CC
+ 2 V min
350 V max DN25D Breakdown Voltage
Full-Scale Settling Time 8 ms typ Settling Time to ±0.1%, C1 = C2 = 10 nF, C3 = 3.3 nF
Output Impedance 25 MΩ typ
AC Loop Voltage Sensitivity 2 µA/V typ 1200 Hz to 2200 Hz
VOLTAGE REGULATOR
Output Voltage (V
CC
)
3 V Mode 2.95/3.05 V min/V max 3 V Nominal. LV Pin Connected to V
CC
3.3 V Mode 3.25/3.35 V min/V max 3.3 V Nominal. LV Pin Connected Through 0.01 µF to V
CC
5 V Mode 4.95/5.05 V min/V max 5 V Nominal. LV Pin Connected to COM
Externally Available Current 3.25 mA min Assuming 4 mA Flowing in the Loop
Line Regulation 1 µV/V typ
Load Regulation 15 µV/mA typ
–2–
(Using DN25D
1
as pass transistor as per Figure 3;
REF IN = REF OUT2; T
A
= T
MIN
to T
MAX
unless otherwise noted)
REV. C
(V
CC
= +3 V to +5 V; REF IN = REF OUT2; T
A
= T
MIN
to T
MAX
unless otherwise noted)
P1-P3P4-P6P7-P9P10-P12P13-P15

AD421BNZ

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Manufacturer:
Analog Devices Inc.
Description:
Digital to Analog Converters - DAC IC 16-BIT
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