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AD2S90APZ Datasheet(PDF) 5 Page - Analog Devices |
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AD2S90APZ Datasheet(HTML) 5 Page - Analog Devices |
5 / 12 page 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 Refer to Figure 4. Positive power supply VDD = +5 V dc ± 5% should be connected to Pin 13 & Pin 14 and negative power supply VSS = –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 VDD, 0 V, or VSS 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 = EO SIN ωt • SINθ S2–S4 = EO SIN ωt • COSθ (1) where: θ = shaft angle SIN ωt = rotor excitation frequency EO = 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: EO SIN ωt • SIN θ COSφ EO SIN ωt • COS θ SINφ (2) An error amplifier subtracts these signals giving: EO SIN θ • (SIN θ COS φ – COS θ SIN φ) or EO SIN 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 VDD R2 R1 S4 S2 VDD VSS Figure 5. Connecting the AD2S90 to a Resolver |
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