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ADVFC32KN Fiches technique(PDF) 3 Page - Analog Devices |
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ADVFC32KN Fiches technique(HTML) 3 Page - Analog Devices |
3 / 6 page ADVFC32 REV. A –3– UNIPOLAR V/F, POSITIVE INPUT VOLTAGE When operated as a V/F converter, the transformation from voltage to frequency is based on a comparison of input signal magnitude to the 1 mA internal current source. A more complete understanding of the ADVFC32 requires a close examination of the internal circuitry of this part. Consider the operation of the ADVFC32 when connected as shown in Figure 1. At the start of a cycle, a current proportional to the Figure 1. Connection Diagram for V/F Conversion, Positive Input Voltage input voltage flows through R3 and R1 to charge integration capacitor C2. As charge builds up on C2, the output voltage of the input amplifier decreases. When the amplifier output volt- age (Pin 13) crosses ground (see Figure 2 at time t1), the comparator triggers a one shot whose time period is determined Figure 2. Voltage-to-Frequency Conversion Waveforms by capacitor C1. Specifically, the one shot time period (in nano- seconds) is: tOS ≅ (C l + 44 pF) × 6.7 kΩ During this period, a current of (1 mA – IIN) flows out of the in- tegration capacitor. The total amount of charge depleted during one cycle is, therefore (1 mA – IIN) × tOS. This charge is replaced during the remainder of the cycle to return the integrator to its original voltage. Since the charge taken out of C2 is equal to the charge that is put on C2 every cycle, (1 mA – IIN) × tOS = IIN × 1 F OUT – t OS or, rearranging terms, FOUT = I IN 1 mA × t OS The complete transfer equation can now be derived by substi- tuting IIN = VIN/RIN and the equation relating C1 and tOS. The final equation describing ADVFC32 operation is: VIIN / RIN 1mA × C 1 + 44 pF ()×6.7kΩ Components should be selected to optimize performance over the desired input voltage and output frequency range using the equations listed below: 3.7 ×107 pF / sec FOUT FS –44 pF C2 = 10 –4 Farads / sec F OUT FS 1000 pF minimum () RIN = VIN FS 0.25 mA R2 ≥ +V LOGIC 8 mA Both RIN and C1 should have very low temperature coefficients as changes in their values will result in a proportionate change in the V/F transfer function. Other component values and tem- perature coefficients are not critical. WARNING! ESD SENSITIVE DEVICE CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the ADVFC32 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. ORDERING GUIDE Part Gain Tempco Temp Range Package Number 1 ppm/ C C Option ADVFC32KN ±75 typ 0 to +70 14-Pin Plastic DIP ADVFC32BH ±100 max –25 to +85 TO-100 ADVFC32SH ±150 max –55 to +125 TO-100 NOTE 1For details on grade and package offerings screened in accordance with MIL-STD-883, refer to the Analog Devices Military Products Databook or current ADVFC32/883B data sheet. Table I. Suggested Values for C1, RIN and C2 VIN FS FOUT FS C1 RIN C2 1 V 10 kHz 3650 pF 4.0 k Ω 0.01 µF 10 V 10 kHz 3650 pF 40 k Ω 0.01 µF 1 V 100 kHz 330 pF 4.0 k Ω 1000 pF 10 V 100 kHz 330 pF 40 k Ω 1000 pF |
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