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AD2S83 bảng dữ liệu(PDF) 9 Page - Analog Devices |
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AD2S83 bảng dữ liệu(HTML) 9 Page - Analog Devices |
9 / 20 page AD2S83 REV. E –8– COMPONENT SELECTION The following instructions describe how to select the external components for the converter in order to achieve the required bandwidth and tracking rate. In all cases the nearest “preferred value” component should be used, and a 5% tolerance will not degrade the overall performance of the converter. Care should be taken that the resistors and capacitors will function over the required operating temperature range. The components should be connected as shown in Figure 1. Free PC compatible software is available to help users select the optimum component values for the AD2S83, and display the transfer gain, phase and small step response. For more detailed information and explanation, see the Circuit Functions and Dynamic Performance section. 1. HF Filter (R1, R2, C1, C2) The function of the HF filter is to remove any dc offset and to reduce the amount of noise present on the signal inputs to the AD2S83, reaching the Phase Sensitive Detector and affecting the outputs. R1 and C2 may be omitted—in which case R2 = R3 and C1 = C3, calculated below—but their use is particularly recommended if noise from switch mode power supplies and brushless motor drive is present. Values should be chosen so that 15 k Ω≤ R1= R2 ≤ 56 kΩ C1 = C2 = 1 2 π R1 f REF and fREF = Reference Frequency (Hz) This filter gives an attenuation of three times at the input to the phase sensitive detector. 2. Gain Scaling Resistor (R4) (See Phase Sensitive Demodula- tor section.) If R1, C2 are used: R4 = E DC 100 × 10 −9 × 1 3 Ω where 100 × 10–9 = current/LSB If R1, C2 are not used: R4 = E DC 100 × 10 –9 Ω where EDC = 160 × 10–3 for 10 bits resolution = 40 × 10–3 for 12 bits = 10 × 10–3 for 14 bits = 2.5 × 10–3 for 16 bits = Scaling of the DC ERROR in volts/LSB 3. AC Coupling of Reference Input (R3, C3) Select R3 and C3 so that there is no significant phase shift at the reference frequency. That is, R 3 = 100 kΩ C 3 > 1 R 3 × f REF F with R3 in Ω. 4. Maximum Tracking Rate (R6) The VCO input resistor R6 sets the maximum tracking rate of the converter and hence the velocity scaling as at the max tracking rate, the velocity output will be 8 V. Decide on your maximum tracking rate, “T,” in revolutions per second. When setting the value for R6, it should be remembered that the linearity of the velocity output is specified across 0 kHz–500 kHz and 500 kHz–1000 kHz. The following conversion can be used to determine the corresponding rps: rps = VCO Rate (Hz ) 2 N Note that “T” must not exceed the maximum tracking rate or 1/16 of the reference frequency. R6 = 6.81 × 10 10 T × n Ω where n = bits per revolution = 1,024 for 10 bits resolution = 4,096 for 12 bits = 16,384 for 14 bits = 65,536 for 16 bits 5. Closed-Loop Bandwidth Selection (C4, C5, R5) a. Choose the closed-loop bandwidth (fBW) required ensuring that the ratio of reference frequency to band- width does not exceed the following guidelines: Resolution Ratio of Reference Frequency/Bandwidth 10 2.5 : 1 12 4 : 1 14 6 : 1 16 7.5 : 1 Typical values may be 100 Hz for a 400 Hz reference fre- quency and 500 Hz to 1000 Hz for a 5 kHz reference frequency. b. Select C4 so that C4 = 21 R6 × f BW 2 F with R6 in Ω and fBW, in Hz selected above. c. C5 is given by C5 = 5 × C4 d. R5 is given by R5 = 4 2 ×π × f BW × C 5 Ω 6. VCO Phase Compensation The following values of C6 and R7 should be connected as close as possible to the VCO output, Pin 41. C6 = 390 pF, R7 = 3.3 kΩ 7. VCO Optimization To optimize the performance of the VCO a capacitor, C7, should be placed across the VCO input and output, Pins 40 and 41. C7 = 150 pF |
Số phần tương tự - AD2S83 |
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Mô tả tương tự - AD2S83 |
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