Datasheet

AD2S90
REV. D
–5–
For more information on the operation of the converter, see
Circuit Dynamics section.
u
S2 TO S4
(COS)
08
S3 TO S1
(SIN)
R2 TO R4
(REF)
908 1808 2708 3608
Figure 4. Electrical and Physical Resolver Representation
Connecting The Converter
Refer to Figure 4. Positive power supply V
DD
= +5 V dc ± 5%
should be connected to Pin 13 & Pin 14 and negative power
supply V
SS
= –5 V dc ± 5% to Pin 12. Reversal of these 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.
Application of V
DD
, 0 V, or V
SS
to NMC will select standard
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.
S3–S1 = E
O
SIN ω t • SIN θ
S2–S4 = E
O
SIN ω t • COS θ (1)
where: θ = shaft angle
SIN ωt = rotor excitation frequency
E
O
= rotor excitation amplitude
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:
E
O
SIN ω t • SIN θ COS φ
E
O
SIN ω t • COS θ SIN φ (2)
An error amplifier subtracts these signals giving:
E
O
SIN θ • (SIN θ COS φ – COS θ SIN φ )
or
E
O
SIN ω t • 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
47mF
10nF
47mF
+5V
–5V
0V (POWER GROUND)
15161718 14
19
20
1
2
3
AD2S90AP
REF
COS LO
COS
AGND
SIN
SIN LO
DGND
76548
13
12
11
10
9
V
DD
R2
R1
S4
S2
V
DD
V
SS
Figure 5. Connecting the AD2S90 to a Resolver