AD2S90

REV. D

–5–

For more information on the operation of the converter, see

Circuit Dynamics section.

S2 TO S4

(COS)

0

S3 TO S1

(SIN)

R2 TO R4

(REF)

90

180

270

360

Figure 4. Electrical and Physical Resolver Representation

Connecting The Converter

± 5%

should be connected to Pin 13 & Pin 14 and negative power

supplies will destroy the device. S3 (SIN) and S2 (COS)

from the resolver should be connected to the SIN and COS pins

of the converter. S1 (SIN) and S4 (COS) from the resolver

should be connected to the SINLO and COSLO pins of the

converter. The maximum signal level of either the SIN or COS

resolver outputs should be 2 V rms

± 10%. The AD2S90

AGND pin is the point at which all analog signal grounds should

be star connected. The SIN LO and COS LO pins on the

AD2S90 should be connected to AGND. Separate screened

twisted cable pairs are recommended for all analog inputs SIN,

COS, and REF. The screens should terminate at the converter

AGND pin.

North marker width selection is controlled by Pin 15, NMC.

90

°, 180° and 360° pulsewidths. If unconnected, the NM pulse

defaults to 90

°. For a more detailed description of the output

formats available see the Position Output section.

RESOLVER FORMAT SIGNALS

A resolver is a rotating transformer which has two stator wind-

ings and one rotor winding. The stator windings are displaced

mechanically by 90

° (see Figure 4). The rotor is excited with an

ac reference. The amplitude of subsequent coupling onto the

stator windings is a function of the position of the rotor (shaft)

relative to the stator. The resolver, therefore, produces two

output voltages (S3–S1, S2–S4) modulated by the SINE and

COSINE of shaft angle. Resolver format signals refer to the

signals derived from the output of a resolver. Equation 1 illus-

trates the output form.

ωt • SINθ

ωt • COSθ

(1)

where:

θ = shaft angle

SIN

ωt = rotor excitation frequency

Principle of Operation

The AD2S90 operates on a Type 2 tracking closed-loop prin-

ciple. The output continually tracks the position of the resolver

without the need for external convert and wait states. As the

transducer moves through a position equivalent to the least

significant bit weighting, the output is updated by one LSB.

On the AD2S90, CLKOUT updates corresponding to one LSB

increment. If we assume that the current word state of the

up-down counter is

φ, S3–S1 is multiplied by COS φ and S2–S4

is multiplied by SIN

φ to give:

ωt • COS θ SINφ

(2)

An error amplifier subtracts these signals giving:

θ • (SIN θ COS φ – COS θ SIN φ)

or

ωt • SIN (θ – φ)

(3)

where (

θ – φ) = angular error

A phase sensitive detector, integrator and voltage controlled

oscillator (VCO) form a closed loop system which seeks to null

sin (

θ – φ). When this is accomplished the word state of the

up/down counter,

φ, equals within the rated accuracy of the

converter, the resolver shaft angle

θ.

OSCILLATOR

TWISTED PAIR

SCREENED

CABLE

S3

S1

S1

S3

S2

S4

POWER RETURN

RESOLVER

10nF

47 F

10nF

47 F

+5V

–5V

0V (POWER GROUND)

15

16

17

18

14

19

20

1

2

3

AD2S90AP

REF

COS LO

COS

AGND

SIN

SIN LO

DGND

7

6

5

48

13

12

11

10

9

R2

R1

S4

S2

Figure 5. Connecting the AD2S90 to a Resolver