Datasheet ADVFC32 (Analog Devices) - 4

ADVFC32 UNIPOLAR V/F, POSITIVE INPUT VOLTAGE
replaced during the remainder of the cycle to return the integra- When operated as a V/F converter, the transformation from tor to its original voltage. Since the charge taken out of C2 is voltage to frequency is based on a comparison of input signal equal to the charge that is put on C2 every cycle, magnitude to the 1 mA internal current source.  1  A more complete understanding of the ADVFC32 requires a (1 mA – I – t IN) × tOS = IIN × OS  F  close examination of the internal circuitry of this part. Consider OUT the operation of the ADVFC32 when connected as shown in or, rearranging terms, Figure 1. At the start of a cycle, a current proportional to the IIN FOUT = 1mA × 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 + 44 pF ( )×6.7kΩ 1 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 – 44 pF F OUT FS 10–4 Farads / sec C 1000 pF minimum ( ) 2 = F Figure 1. Connection Diagram for V/F Conversion, OUT FS Positive Input Voltage VIN FS input voltage flows through R3 and R1 to charge integration RIN = 0.25mA capacitor C2. As charge builds up on C2, the output voltage of the input amplifier decreases. When the amplifier output volt- +VLOGIC R age (Pin 13) crosses ground (see Figure 2 at time t 2 ≥ 1), the 8 mA comparator triggers a one shot whose time period is determined Both RIN and C1 should have very low temperature coefficients by capacitor C1. Specifically, the one shot time period (in nano- as changes in their values will result in a proportionate change seconds) is: in the V/F transfer function. Other component values and tem- tOS ≅ (Cl + 44 pF) × 6.7 kΩ perature coefficients are not critical.
Table I. Suggested Values for C1, RIN and C2 VIN FS FOUT FS C1 RIN C2
1 V 10 kHz 3650 pF 4.0 kΩ 0.01 µF 10 V 10 kHz 3650 pF 40 kΩ 0.01 µF 1 V 100 kHz 330 pF 4.0 kΩ 1000 pF 10 V 100 kHz 330 pF 40 kΩ 1000 pF
ORDERING GUIDE Part Gain Tempco Temp Range Package Number1 ppm/
ⴗ
C
ⴗ
C Option
ADVFC32KN ±75 typ 0 to 70 14-Pin Plastic DIP ADVFC32BH ±100 max –25 to +85 TO-100 Figure 2. Voltage-to-Frequency Conversion Waveforms ADVFC32SH ±150 max –55 to +125 TO-100 During this period, a current of (1 mA – IIN) flows out of the NOTE integration capacitor. The total amount of charge depleted 1For details on grade and package offerings screened in accordance with MIL-STD-883, during one cycle is, therefore (1 mA – IIN) × tOS. This charge is refer to the Analog Devices Military Products Databook or current ADVFC32/883B data sheet.
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
WARNING!
the ADVFC32 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are
ESD SENSITIVE DEVICE
recommended to avoid performance degradation or loss of functionality. REV. B –3–