ad420-32-reel Analog Devices, Inc., ad420-32-reel Datasheet

ad420-32-reel

Manufacturer Part Number

ad420-32-reel

Description

Serial Input 16-bit 4 Ma-20 Ma, 0 Ma-20 Ma Dac

Manufacturer

Analog Devices, Inc.

Datasheet

1.AD420-32-REEL.pdf (11 pages)

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PRODUCT DESCRIPTION

The AD420 is a complete digital to current loop output con-

verter, designed to meet the needs of the industrial control

market. It provides a high precision, fully integrated, low cost

single-chip solution for generating current loop signals in a

compact 24-lead SOIC or PDIP package.

The output current range can be programmed to 4 mA–20 mA,

0 mA–20 mA or an overrange function of 0 mA–24 mA. The

AD420 can alternatively provide a voltage output from a sepa-

rate pin that can be configured to provide 0 V–5 V, 0 V–10 V,

amplifier.

The 3.3M Baud serial input logic design minimizes the cost of

galvanic isolation and allows for simple connection to com-

monly used microprocessors. It can be used in three-wire or

asynchronous mode and a serial-out pin is provided to allow

daisy chaining of multiple DACs on the current loop side of the

isolation barrier.

The AD420 uses sigma-delta (

16-bit monotonicity at very low cost. Full-scale settling to 0.1%

occurs within 3 ms. The only external components that are re-

quired (in addition to normal transient protection circuitry) are

two low cost capacitors which are used in the DAC output filter.

If the AD420 is going to be used at extreme temperatures and

supply voltages, an external output transistor can be used to

minimize power dissipation on the chip via the “BOOST” pin.

The FAULT DETECT pin signals when an open circuit occurs

in the loop. The on-chip voltage reference can be used to supply

a precision +5 V to external components in addition to the

AD420 or, if the user desires temperature stability exceeding

25 ppm/ C, an external precision reference such as the AD586

can be used as the reference.

SPI is a registered trademark of Motorola.

MICROWIRE is a registered trademark of National Semiconductor.

REV. F

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.

5 V or 10 V with the addition of a single external buffer

FEATURES

4 mA–20 mA, 0 mA–20 mA or 0 mA–24 mA Current Output

16-Bit Resolution and Monotonicity

Flexible Serial Digital Interface (3.3 MBPS)

On-Chip Loop Fault Detection

On-Chip 5 V Reference (25 ppm/ C Max)

Asynchronous CLEAR Function

Maximum Power Supply Range of 32 V

Output Loop Compliance of 0 V to V

24-Lead SOIC and PDIP Packages

0.012% Max Integral Nonlinearity

0.05% Max Offset (Trimmable)

0.15% Max Total Output Error (Trimmable)

) DAC technology to achieve

– 2.5 V

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

Tel: 781/329-4700

Fax: 781/326-8703

The AD420 is available in a 24-lead SOIC and PDIP over the

industrial temperature range of –40 C to +85 C.

PRODUCT HIGHLIGHTS

1. The AD420 is a single chip solution for generating 4 mA–

2. The AD420 is specified with a power supply range

3. The flexible serial input can be used in three-wire mode

4. The serial data out pin can be used to daisy chain any num-

5. At power-up the AD420 initializes its output to the low end

6. The AD420 has an asynchronous CLEAR pin which sends

7. The AD420 BOOST pin accommodates an external transis-

8. The offset of 0.05% and total output error of 0.15% can

4 mA–20 mA, 0 mA–20 mA DAC

DATA OUT

SELECT 1

SELECT 2

REF OUT

DATA IN

20 mA or 0 mA–20 mA signals at the “controller end” of the

current loop.

from 12 V to 32 V. Output loop compliance is 0 V to

with SPI

chronous mode which minimizes the number of control

signals required.

ber of AD420s together in three-wire mode.

of the selected range.

the output to the low end of the selected range (0 mA,

4 mA, or 0 V).

tor to off-load power dissipation from the chip.

be trimmed if desired, using two external potentiometers.

CLEAR

CLOCK

RANGE

LATCH

REF IN

– 2.5 V.

FUNCTIONAL BLOCK DIAGRAM

DATA I/P

or MICROWIRE

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

REFERENCE

OFFSET

CLOCK

16-BIT

TRIM

DAC

AD420

Serial Input 16-Bit

CAP 1

SWITCHED

FILTERING

CURRENT

SOURCES

microcontrollers, or in asyn-

AND

CAP 2

GND

1.25k

AD420

BOOST

FAULT

DETECT

OUT

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ad420-32-reel Summary of contents

Page 1

... RANGE SELECT 1 RANGE SELECT 2 The AD420 is available in a 24-lead SOIC and PDIP over the industrial temperature range of – +85 C. PRODUCT HIGHLIGHTS 1. The AD420 is a single chip solution for generating 4 mA– mA–20 mA signals at the “controller end” of the current loop ...

Page 2

... AD420–SPECIFICATIONS Parameter RESOLUTION I CHARACTERISTICS OUT Operating Current Ranges Current Loop Voltage Compliance 2 Settling Time (to 0.1% of FS) Output Impedance (Current Mode) 3 Accuracy Monotonicity Integral Nonlinearity Offset ( mA + Offset Drift Total Output Error ( mA) (T Total Output Error Drift ...

Page 3

... ABSOLUTE MAXIMUM RATINGS GND CC AD420AR/AN- GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V OUT Digital Inputs to GND . . . . . . . . . . . . . . . . . . . –0 Digital Output to GND . . . . . . . . . . . . . –0 and REF OUT: Outputs Safe for Indefinite Short to Ground LL Storage Temperature . . . . . . . . . . . . . . . . . . – +150 C Lead Temperature (Soldering, 10 sec +300 C Thermal Impedance: SOIC (R) Package ...

Page 4

... The DAC output updates when the STOP bit is received. In the case of a “framing error” (the STOP bit sampled the AD420 will output a pulse at the DATA OUT pin one clock period wide during the clock period subsequent to sampling the STOP bit. The DAC output will not update if a “framing error” ...

Page 5

... Reference Input. Offset Adjust. Voltage Output. Current Output. Connect to an external transistor to reduce the power dissipated in the AD420 output transistor, if desired. These pins are used for internal filtering. Connect capacitors between each of these pins and V . Refer to the description of current output operation. ...

Page 6

... FAULT DETECT output becomes active. Instead, the signal is generated when the internal ampli- fier in the output stage of the AD420 has less than approximately one volt remaining of drive capability (when the gate of the output PMOS transistor nearly reaches ground). Thus the FAULT DETECT output activates slightly before the compli- ance limit is reached ...

Page 7

... To prevent this voltage from exceeding the supply rails connect protective diodes between I and each of V OUT VOLTAGE-MODE OUTPUT Since the AD420 is a single supply device necessary to add an external buffer amplifier to the V OUT tion of bipolar output voltage ranges as shown in Figure ...

Page 8

... The three-wire interface mode can utilize the serial DATA OUT for easy interface to multiple DACs. To program the two AD420s in Figure 8, 32 data bits are required. The first 16 bits are clocked into the input shift register of DAC1. The next 16 bits transmitted pass the first 16 bits from the DATA OUT pin of DAC1 to the input register of DAC2 ...

Page 9

... Figure 12. External Boost Configuration The external boost capability has been developed for those users who may wish to use the AD420, in the SOIC package, at the extremes of the supply voltage, load current, and temperature range. The PDIP package (because of its lower thermal resis- tance) will operate safely over the entire specified voltage, tem- perature, and load current ranges without the boost transistor ...

Page 10

... GND Figure 14. Output Transient Voltage Protection BOARD LAYOUT AND GROUNDING The AD420 ground pin, designated GND, is the “high quality” ground reference point for the device. Any external loads on the REF OUT and V this reference point. Analog and digital ground currents should not share a common path ...

Page 11

... BSC 24-Lead Small Outline (SOIC) (R-24) 0.6141 (15.60) 0.5985 (15.20 0.1043 (2.65) PIN 1 0.0926 (2.35) 0.0500 0.0192 (0.49) SEATING 0.0125 (0.32) (1.27) 0.0138 (0.35) PLANE BSC 0.0091 (0.23) –11– AD420 0.325 (8.25) 0.195 (4.95) 0.300 (7.62) 0.115 (2.93) 0.015 (0.381) 0.008 (0.204) 0.0291 (0.74) x 45° 0.0098 (0.25) 0.0500 (1.27) 8° 0° 0.0157 (0.40) ...

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