Analog Devices AD670AD, AD670SD, AD670KN, AD670JP, AD670JN Datasheet

FUNCTIONAL BLOCK DIAGRAM

REV. A

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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

Low Cost Signal

Conditioning 8-Bit ADC

AD670

FEATURES

Complete 8-Bit Signal Conditioning A/D Converter

Including Instrumentation Amp and Reference

Microprocessor Bus Interface

10 ms Conversion Speed

Flexible Input Stage: Instrumentation Amp Front End

Provides Differential Inputs and High Common-Mode

Rejection

No User Trims Required

No Missing Codes Over Temperature

Single +5 V Supply Operation

Convenient Input Ranges

20-Pin DIP or Surface-Mount Package

Low Cost Monolithic Construction

MIL-STD-883B Compliant Versions Available

GENERAL DESCRIPTION

The AD670 is a complete 8-bit signal conditioning analog-

to-digital converter. It consists of an instrumentation amplifier

front end along with a DAC, comparator, successive approxima-

tion register (SAR), precision voltage reference, and a three-

state output buffer on a single monolithic chip. No external

components or user trims are required to interface, with full

accuracy, an analog system to an 8-bit data bus. The AD670

will operate on the +5 V system supply. The input stage pro-

vides differential inputs with excellent common-mode rejection

and allows direct interface to a variety of transducers.

The device is configured with input scaling resistors to permit

two input ranges: 0 mV to 255 mV (1 mV/LSB) and 0 to 2.55 V

(10 mV/LSB). The AD670 can be configured for both unipolar

and bipolar inputs over these ranges. The differential inputs and

common-mode rejection of this front end are useful in applica-

tions such as conversion of transducer signals superimposed on

common-mode voltages.

The AD670 incorporates advanced circuit design and proven

processing technology. The successive approximation function

is implemented with I

2

L (integrated injection logic). Thin-film

SiCr resistors provide the stability required to prevent missing

codes over the entire operating temperature range while laser

wafer trimming of the resistor ladder permits calibration of the

device to within ±1 LSB. Thus, no user trims for gain or offset

are required. Conversion time of the device is 10 µs.

The AD670 is available in four package types and five grades.

The J and K grades are specified over 0°C to +70°C and come

in 20-pin plastic DIP packages or 20-terminal PLCC packages.

The A and B grades (–40°C to +85°C) and the S grade (–55°C

to +125°C) come in 20-pin ceramic DIP packages.

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

Tel: [phone] Fax: [phone]

The S grade is also available with optional processing to

MIL-STD-883 in 20-pin ceramic DIP or 20-terminal LCC

packages. The Analog Devices Military Products Databook

should be consulted for detailed specifications.

PRODUCT HIGHLIGHTS

1. The AD670 is a complete 8-bit A/D including three-state

outputs and microprocessor control for direct connection to

8-bit data buses. No external components are required to

perform a conversion.

2. The flexible input stage features a differential instrumenta-

tion amp input with excellent common-mode rejection. This

allows direct interface to a variety of transducers without

preamplification.

3. No user trims are required for 8-bit accurate performance.

4. Operation from a single +5 V supply allows the AD670 to

run off of the microprocessor’s supply.

5. Four convenient input ranges (two unipolar and two bipolar)

are available through internal scaling resistors: 0 mV to

255 mV (1 mV/LSB) and 0 V to 2.55 V (10 mV/LSB).

6. Software control of the output mode is provided. The user

can easily select unipolar or bipolar inputs and binary or 2s

complement output codes.

Model AD670J AD670K

Min Typ Max Min Typ Max Units

OPERATING TEMPERATURE RANGE 0 +70 0 +70 °C

RESOLUTION 8 8 Bit

CONVERSION TIME 10 10 µs

RELATIVE ACCURACY 61/2 61/4 LSB

T

MIN

to T

MAX

6l/2 61/2 LSB

DIFFERENTIAL LINEARITY ERROR

1

T

MIN

to T

MAX

GUARANTEED NO MISSING CODES ALL GRADES

GAIN ACCURACY

@ +25°C 61.5 60.75 LSB

T

MIN

to T

MAX

62.0 61.0 LSB

UNIPOLAR ZERO ERROR

@ +25°C 61.5 60.75 LSB

T

MIN

to T

MAX

62.0 61.0 LSB

BIPOLAR ZERO ERROR

@ +25°C 61.5 60.75 LSB

T

MIN

to T

MAX

62.0 61.0 LSB

ANALOG INPUT RANGES

DIFFERENTIAL (–V

IN

to +V

IN

)

Low Range 0 to +255 0 to +255 mV

–128 to +127 –128 to +127 mV

High Range 0 to +2.55 0 to +2.55 V

–1.28 to +1.27 –1.28 to +1.27 V

ABSOLUTE (Inputs to Power GND)

Low Range T

MIN

to T

MAX

–0.150 V

CC

– 3.4 –0.150 V

CC

– 3.4 V

High Range T

MIN

to T

MAX

–1.50 V

CC

–1.50 V

CC

V

BIAS CURRENT (255 mV RANGE)

T

MIN

to T

MAX

200 500 200 500 nA

OFFSET CURRENT (255 mV RANGE)

T

MIN

to T

MAX

40 200 40 200 nA

2.55 V RANGE INPUT RESISTANCE 8.0 12.0 8.0 12.0 kΩ

2.55 V RANGE FULL-SCALE MATCH

+ AND – INPUT ±1/2 ±1/2 LSB

COMMON-MODE REJECTION

RATIO (255 mV RANGE) 11LSB

COMMON-MODE REJECTION

RATIO (2.55 V RANGE) 1 1 LSB

POWER SUPPLY

Operating Range 4.5 5.5 4.5 5.5 V

Current I

CC

30 45 30 45 mA

Rejection Ratio T

MIN

to T

MAX

0.015 0.015 % of FS/%

DIGITAL OUTPUTS

SINK CURRENT (V

OUT

= 0.4 V)

T

MIN

to T

MAX

1.6 1.6 mA

SOURCE CURRENT (V

OUT

= 2.4 V)

T

MIN

to T

MAX

0.5 0.5 mA

THREE-STATE LEAKAGE CURRENT 640 640 µA

OUTPUT CAPACITANCE 5 5 pF

DIGITAL INPUT VOLTAGE

V

INL

0.8 0.8 V

V

INH

2.0 2.0 V

DIGITAL INPUT CURRENT

(0 ≤ V

IN

≤ +5 V)

I

INL

–100 –100 µA

I

INH

+100 +100 µA

INPUT CAPACITANCE 10 10 pF

NOTES

1

Tested at V

CC

= 4 5 V, 5.0 V and 5.5 V.

Specifications shown in boldface are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. All min and max specifications

are guaranteed although only those shown in boldface are tested on all production units.

Specifications subject to change without notice.

AD670–SPECIFICATIONS

(@ V

CC

= +5 V and

+258C,

unless otherwise noted)

REV. A

–2–

Model AD670A AD670B AD670S

Min Typ Max Min Typ Max Min Typ Max Units

OPERATING TEMPERATURE RANGE –40 +85 –40 +85 –55 +125 °C

RESOLUTION 8 8 8 Bit

CONVERSION TIME 10 10 10 µs

RELATIVE ACCURACY 61/2 61/4 61/2 LSB

T

MIN

to T

MAX

61/2 61/2 61 LSB

DIFFERENTIAL LINEARITY ERROR

1

T

MIN

to T

MAX

GUARANTEED NO MISSING CODES ALL GRADES

GAIN ACCURACY

@ +25°C 61.5 60.75 61.5 LSB

T

MIN

to T

MAX

62.5 61.5 62.5 LSB

UNIPOLAR ZERO ERROR

@ +25°C 61.0 60.5 61.0 LSB

T

MIN

to T

MAX

62.0 61.0 62.0 LSB

BIPOLAR ZERO ERROR

@ +25°C 61.0 60.5 61.0 LSB

T

MIN

to T

MAX

62.0 61.0 62.0 LSB

ANALOG INPUT RANGES

DIFFERENTIAL ( –V

IN

to +V

IN

)

Low Range 0 to +255 0 to +255 0 to +255 mV

–128 to +127 –128 to +127 –128 to +127 mV

High Range 0 to +2.55 0 to +2.55 0 to +2.55 V

–1.28 to +1.27 –1.28 to +1.27 –1.28 to +1.27 V

ABSOLUTE (Inputs to Power GND)

Low Range T

MIN

to T

MAX

–0.150 V

CC

– 3.5 –0.150 V

CC

– 3.5 –0.150 V

CC

– 3.5 V

High Range T

MIN

to T

MAX

–1.50 V

CC

–1.50 V

CC

–1.50 V

CC

V

BIAS CURRENT (255 mV RANGE)

T

MIN

to T

MAX

200 500 200 500 200 750 nA

OFFSET CURRENT (255 mV RANGE)

T

MIN

to T

MAX

40 200 40 200 40 200 nA

2.55 V RANGE INPUT RESISTANCE 8.0 12.0 8.0 12.0 8.0 12.0 kΩ

2.55 V RANGE FULL-SCALE MATCH

+ AND – INPUT ±1/2 ±1/2 ±1/2 LSB

COMMON-MODE REJECTION

RATIO (255 mV RANGE) 111LSB

COMMON-MODE REJECTION

RATIO (2.55 V RANGE) 1 1 1 LSB

POWER SUPPLY

Operating Range 4.5 5.5 4.5 5.5 4.75 5.5 V

Current I

CC

30 45 30 45 30 45 mA

Rejection Ratio T

MIN

to T

MAX

0.015 0.015 0.015 % of FS/%

DIGITAL OUTPUTS

SINK CURRENT (V

OUT

= 0.4 V)

T

MIN

to T

MAX

1.6 1.6 1.6 mA

SOURCE CURRENT (V

OUT

= 2.4 V)

T

MIN

to T

MAX

0.5 0.5 0.5 mA

THREE-STATE LEAKAGE CURRENT 640 640 640 µA

OUTPUT CAPACITANCE 5 5 5 pF

DIGITAL INPUT VOLTAGE

V

INL

0.8 0.8 0.7 V

V

INH

2.0 2.0 2.0 V

DIGITAL INPUT CURRENT

(0 ≤ V

IN

≤ +5 V)

I

INL

–100 –100 –100 µA

I

INH

+100 +100 + 100 µA

INPUT CAPACITANCE 10 10 10 pF

NOTES

1

Tested at V

CC

= 4.5 V, 5.0 V and 5.5 V for A, B grades; 4.75 V, 5.0 V and 5.5 V for S grade.

Specifications shown in boldface are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. All min and max specifications

are guaranteed, although only those shown in boldface are tested on all production units.

Specifications subject to change without notice.

AD670

REV. A

–3–

AD670

REV. A

–4–

ORDERING GUIDE

Temperature Relative Accuracy Gain Accuracy

Model

1

Range @ +258C @ +258C Package Option

2

AD670JN 0°C to +70°C ±1/2 LSB ±1.5 LSB Plastic DIP (N-20)

AD670JP 0°C to +70°C ±1/2 LSB ±1.5 LSB PLCC (P-20A)

AD670KN 0°C to +70°C ±1/4 LSB ±0.75 LSB Plastic DIP (N-20)

AD670KP 0°C to +70°C ±1/4 LSB ±0.75 LSB PLCC (P-20A)

AD670AD –40°C to +85°C ±1/2 LSB ±1.5 LSB Ceramic DIP (D-20)

AD670BD –40°C to +85°C ±1/4 LSB ±0.75 LSB Ceramic DIP (D-20)

AD670SD –55°C to +125°C ±1/2 LSB ±1.5 LSB Ceramic DIP (D-20)

NOTES

1

For details on grade and package offerings screened in accordance with MIL-STD-883 refer to the Analog Devices

Military Products Databook.

2

D = Ceramic DIP; N = Plastic DIP; P = Plastic Leaded Chip Carrier.

Figure 1. AD670 Block Diagram and Terminal

Configuration (AII Packages)

ABSOLUTE MAXIMUM RATINGS*

V

CC

to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V to +7.5 V

Digital Inputs (Pins 11–15) . . . . . . . . . . . –0.5 V to V

CC

+0.5 V

Digital Outputs (Pins 1–9) . Momentary Short to V

CC

or Ground

Analog Inputs (Pins 16–19) . . . . . . . . . . . . . . . –30 V to +30 V

Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 mW

Storage Temperature Range . . . . . . . . . . . . . –65°C to +150°C

Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . +300°C

*Stresses above those listed under “Absolute Maximum Ratings” may cause

permanent damage to the device. This is a stress rating only and functional

operation of the device at them or any other conditions above those indicated in

the operational sections of this specification is not implied. Exposure to absolute

maximum rating conditions for extended periods may affect device reliability.

CIRCUIT OPERATION/FUNCTIONAL DESCRIPTION

The AD670 is a functionally complete 8-bit signal conditioning

A/D converter with microprocessor compatibility. The input

section uses an instrumentation amplifier to accomplish the

voltage to current conversion. This front end provides a high

impedance, low bias current differential amplifier. The com-

mon-mode range allows the user to directly interface the device

to a variety of transducers.

The AID conversions are controlled by R/

W, CS, and CE. The

R/

W line directs the converter to read or start a conversion. A

minimum write/start pulse of 300 ns is required on either

CE or

CS. The STATUS line goes high, indicating that a conversion is

in process. The conversion thus begun, the internal 8-bit DAC

is sequenced from MSB to LSB using a novel successive ap-

proximation technique. In conventional designs, the DAC is

stepped through the bits by a clock. This can be thought of as a

static design since the speed at which the DAC is sequenced is

determined solely by the clock. No clock is used in the AD670.

Instead, a “dynamic SAR” is created consisting of a string of in-

verters with taps along the delay line. Sections of the delay line

between taps act as one shots. The pulses are used to set and re-

set the DAC’s bits and strobe the comparator. When strobed,

the comparator then determines whether the addition of each

successively weighted bit current causes the DAC current sum

to be greater or less than the input current. If the sum is less,

the bit is turned off. After all bits are tested, the SAR holds an

8-bit code representing the input signal to within 1/2 LSB

accuracy. Ease of implementation and reduced dependence on

process related variables make this an attractive approach to a

successive approximation design.

The SAR provides an end-of-conversion signal to the control

logic which then brings the STATUS line low. Data outputs re-

main in a high impedance state until R/

W is brought high with

CE and CS low and allows the converter to be read. Bringing

CE or CS high during the valid data period ends the read cycle.

The output buffers cannot be enabled during a conversion. Any

convert start commands will be ignored until the conversion

cycle is completed; once a conversion cycle has been started it

cannot be stopped or restarted.

The AD670 provides the user with a great deal of flexibility by

offering two input spans and formats and a choice of output

codes. Input format and input range can each be selected. The

BPO/

UPO pin controls a switch which injects a bipolar offset

current of a value equal to the MSB less 1/2 LSB into the sum-

ming node of the comparator to offset the DAC output. Two

precision 10 to 1 attenuators are included on board to provide

input range selection of 0 V to 2.55 V or 0 mV to 255 mV. Ad-

ditional ranges of –1.28 V to 1.27 V and –128 mV to 127 mV

are possible if the BPO/

UPO switch is high when the conversion

is started. Finally, output coding can be chosen using the FOR-

MAT pin when the conversion is started. In the bipolar mode

and with a Logic 1 on FORMAT, the output is in two’s comple-

ment; with a Logic 0, the output is offset binary.