AD421BR Analog Devices Inc, AD421BR Datasheet

AD421BR

Manufacturer Part Number

AD421BR

Description

Digital/Analog Converter IC Interface Type:Serial

Manufacturer

Analog Devices Inc

Datasheet

1.AD421BRZRL.pdf (14 pages)

Specifications of AD421BR

Number Of Bits

Package/case

16-SOIC-WIDE

Leaded Process Compatible

Features

Loop-Powered 4-20 MA DAC

Linearity Error (inl)

0.01LSB

Mounting Type

Surface Mount

Rohs Status

RoHS non-compliant

Settling Time

8µs

Data Interface

Serial

Number Of Converters

Voltage Supply Source

Single Supply

Power Dissipation (max)

1.95mW

Operating Temperature

-40°C ~ 85°C

Package / Case

16-SOIC (0.300", 7.5mm Width)

Number Of Channels

Resolution

16b

Interface Type

Serial (3-Wire)

Single Supply Voltage (typ)

3.3/5V

Dual Supply Voltage (typ)

Not RequiredV

Architecture

Delta-Sigma

Power Supply Requirement

Single

Output Type

Current

Single Supply Voltage (min)

2.95V

Single Supply Voltage (max)

5.05V

Dual Supply Voltage (min)

Not RequiredV

Dual Supply Voltage (max)

Not RequiredV

Operating Temp Range

-40C to 85C

Operating Temperature Classification

Industrial

Mounting

Surface Mount

Pin Count

Package Type

SOIC W

Lead Free Status / RoHS Status

Contains lead / RoHS non-compliant

Lead Free Status / RoHS Status

Contains lead / RoHS non-compliant

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Download datasheet (172Kb)

HART is a registered trademark of the HART Communication

Foundation.

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.

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.

FEATURES

4 mA to 20 mA Current Output

HART

16-Bit Resolution and Monotonicity

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

0.01% Integral Nonlinearity

Compatible

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

Fax: 781/326-8703

PRODUCT HIGHLIGHTS

1. The AD421 is a single chip, high performance, low cost

2. The AD421’s regulated supply voltage can be used to power

3. The AD421’s on-chip references can provide a precision

4. The AD421 is fully compatible with standard HART cir-

5. With the addition of a single discrete transistor, the AD421

6. The AD421 converts the digital data to current with 16-bit

7. The AD421 features a programmable alarm current capabil-

CLOCK

LATCH

DATA

solution for generating 4 mA to 20 mA signals for smart

industrial control transmitters.

any additional circuits in the transmitter. The regulated

output value is pin selectable as either +3 V, +3.3 V or +5 V.

reference voltage to other devices in the system. This refer-

ence voltage can be either +1.25 V or +2.5 V.

cuitry or other similar FSK protocols.

can be operated from V

breakdown voltage of the pass transistor.

resolution and monotonicity. Full-scale settling time to

± 0.1% typically occurs within 8 ms.

ity that allows the transmitter to send out of range currents to

indicate a transducer fault.

REF IN

(+2.5V)

INPUT SHIFT

DAC LATCH

POWER-ON

RESET

FUNCTIONAL BLOCK DIAGRAM

REF OUT1

(+1.25V)

World Wide Web Site: http://www.analog.com

AD421

OSCILLATOR

DELTA DAC

SIGMA-

16-BIT

LOCAL

REF OUT2

4 mA to 20 mA DAC

COM

(+2.5V)

+ 2 V min to a maximum of the

REFERENCE

BANDGAP

SWITCHED

FILTERING

CURRENT

SOURCES

C1 C2 C3

Loop-Powered

AND

112.5k

134k

121k

80k

AD421

75k

BOOST

DRIVE

COMP

LOOP

RTN

Related parts for AD421BR

AD421BR Summary of contents

Page 1

FEATURES Current Output ® HART Compatible 16-Bit Resolution and Monotonicity 0.01% Integral Nonlinearity Regulator Output 2.5 V and 1.25 V Precision Reference 750 A Quiescent Current max Programmable Alarm ...

Page 2

AD421–LOOP-POWERED SPECIFICATIONS Parameter OUTPUT CHARACTERISTICS 3 Current Loop Voltage Compliance Full-Scale Settling Time Output Impedance AC Loop Voltage Sensitivity VOLTAGE REGULATOR Output Voltage ( Mode 3.3 V Mode 5 V Mode Externally Available Current Line Regulation ...

Page 3

TIMING CHARACTERISTICS Parameter (B Versions) t 100 NOTES 1 Guaranteed by characterization at initial product ...

Page 4

... REF OUT2 REF IN LV LATCH CLOCK DATA LOOP RTN ORDERING GUIDE Temperature Model Range AD421BN –40°C to +85°C AD421BR –40°C to +85°C AD421BRRL –40°C to +85°C EVAL-AD421EB Evaluation Board *N = Plastic DIP SOIC. –4– DIP and SOIC BOOST 3 ...

Page 5

Pin No. Mnemonic Function 1 REF OUT1 Reference Output 1. A precision +1.25 V reference is provided at this pin intended as a precision ref- erence source for other devices in the transmitter. REF OUT1 is a buffered ...

Page 6

AD421 CIRCUIT DESCRIPTION The AD421 is designed for use in loop-powered 4–20 mA smart transmitter applications. A smart transmitter remote in- strument, controls its current output signal on the same pair of wires from which it receives its ...

Page 7

SWITCHED AD421 CURRENT SOURCES 80k 40 Figure 4. Current Amplifier The BOOST pin is normally tied to the V input code varies from all zeros to full scale, the output current from the NPN transistor and thus the total loop ...

Page 8

AD421 of 11.147 mA. With 16 clock pulses between consecutive latch signals data written is for normal operation. Table II. Ideal Input/Output Code Table for Operation Code 0000 0000 0000 ...

Page 9

The HC11 generates the requisite eight clock pulses with data valid on the rising edges. After the MSBY is transmitted, the least significant byte (LSBY) is loaded from memory and transmitted in a similar fashion. To complete the transfer, the ...

Page 10

AD421 A capacitor of 0.01 µF connected between COMP and DRIVE is required to stabilize the feedback loop formed with the regulator op amp and the external pass transistor. An external snubber circuit of 1 kΩ and 1000 pF is ...

Page 11

SENSORS RTD REF ANALOG TO AMBIENT DIGITAL TEMP CONVERTER SENSOR AD7714/ AD7715 MCLK IN MCLK OUT CS DATA OUT SCLK DATA IN AGND DGND Figure 14. AD421 in Smart Transmitter Application ...

Page 12

AD421 0 SENSORS RTD REF 100k ANALOG TO AMBIENT DIGITAL TEMP CONVERTER SENSOR AD7714/ AD7715 MCLK IN MCLK OUT CS DATA OUT SCLK DATA IN AGND DGND Figure 17. AD421 in HART ...

Page 13

Battery Backup Figure 19 shows an application circuit for the AD421 where the micro and memory sections of the circuitry are protected against losing data if the loop is broken. The backup circuit switches from V to battery voltage without ...

Page 14

AD421 0.210 (5.33) 0.160 (4.06) 0.115 (2.93) 0.0118 (0.30) 0.0040 (0.10) OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 16-Lead Plastic DIP (N-16) 0.840 (21.34) 0.745 (18.92 0.280 (7.11) 0.240 (6.10 0.325 (8.26) 0.300 (7.62) PIN ...

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