AD2S93

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

Tel: 617/329-4700

Fax: 617/326-8703

a

Low Cost

LVDT-to-Digital Converter

FUNCTIONAL BLOCK DIAGRAM

DEMODIN

CLKOUT

DEMOD OUT

ERROR

AMP

LOS

LATCHES

FREQUENCY

SHAPING

VCO

PHASE

SENSITIVE

DEMODULATOR

C1

C2

R2

VEL

UP-DOWN

COUNTER

REFERENCE

(PRIMARY

EXCITATION)

DIFFERENTIAL

(SECONDARY

VOLTAGE)

REF

A

B

LOS

GAIN

V

DD

OVR

UNR

NULL

CS

DATA

SCLK

ACERROR

AC RATIO

BRIDGE

DIFF

DECODE

LOGIC

C3

AD2S93

INTIN

R4

R3

SERIAL

INTERFACE

DIR

R5

R1

C4

R6

R7

VCO GAIN

FEATURES

Full Function Monolithic LVDT-to-Digital Converter

Absolute Serial Data Output

Uncommitted Differential Input

Repeatability

Remote Diagnostics

14-Bit Resolution

Industrial Temperature Range

28-Pin PLCC

Low Power

APPLICATIONS

Industrial Gauging

Industrial Process Control

Linear Positioning Systems

Linear Actuator Control

Automotive Motion Sensing and Control

Torque Sensing Conditioner

AC Strain Gages Conditioning

Avionics

REV. A

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 AD2S93 is a complete 14-bit resolution tracking LVDT-to-

digital converter. A Type II tracking loop is employed to track

the A–B input and produce a digital output equal to (A–B)/

(REF/2), where REF is a fixed amplitude ac reference phase co-

herent with the A–B input. This allows the measurement of any

2-, 3-, 4- and 5-wire LVDT or linear amplitude modulated in-

put. The operating frequency range is from 360 Hz to 10 kHz

with user definable bandwidth set externally within a range of

45 Hz to 1250 Hz.

The AD2S93 has a 16-bit serial output. The MSB (LOS), read

first, indicates a loss of the signal A, B, or reference inputs to the

converter or transducer. The second and third MSBs are flags

indicating whether [–REF/2 (UNR)

≤ A–B ≤ +REF/2 (OVR]) is

outside the linear operating range of the converter. The dis-

placement data is presented as 13-bit offset binary giving a

±12-

bit operating range. LOS, OVR and UNR are pinned out on

the device, in addition a NULL flag is available which is set

when (A–B) = 0.

Absolute displacement information is accessed when CS is taken

LO followed by the application of an external clock (SCLK)

with a maximum rate of 2 MHz. Data is read MSB first. When

CS

is high the DATA output is high impedance; this allows

daisy chaining of more than one converter onto a common bus.

The A, B differential input allows the user to scale the A, B in-

puts between 1 and 10. This enables the user to accurately set

up the inputs matching the REF input to the DIFF output. The

DIFF output is the resultant A–B. The AD2S93 operates using

±5 V ± 5% power supplies and is fabricated on Analog Devices’

linear compatible CMOS process (LC

is a mixed technology process that combines precision bipolar

circuits with low power logic.

PRODUCT HIGHLIGHTS

Complete LVDT-to-Digital Interface.

The AD2S93 pro-

vides the complete solution for digitizing LVDT signals to 14-

bit resolution.

Serial 16-Bit Output Data.

One 16-bit read from the

AD2S93 determines input signal continuity (LOS), over and

underrange detection and 13 bits of offset binary displacement

information.

High Accuracy Grade in Low Cost Package.

0.05% and

0.1% integral linearity over the full –40

°C to +85°C operating

temperature range.

Uncommitted Differential Input.

Allows configuration of 2-,

3-, 4- and 5-wire LVDTs.

Multiple Converter Interfacing.

High impedance data out-

put and a simple three-wire interface reduces cabling and elimi-

nates bus contention.

Low Power

. 70 mW power consumption (typ).