ADVFC32 Просмотр технического описания (PDF) - Analog Devices
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ADVFC32 Datasheet PDF : 7 Pages
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ADVFC32
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
by capacitor C1. Specifically, the one shot time period (in nano-
seconds) is:
tOS ≅ (Cl + 44 pF) × 6.7 kΩ
replaced during the remainder of the cycle to return the integra-
tor to its original voltage. Since the charge taken out of C2 is
equal to the charge that is put on C2 every cycle,
1
(1 mA – IIN) × tOS = IIN × FOUT – tOS
or, rearranging terms,
FOUT
=
I IN
1 mA × tOS
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:
VINI / RIN
( ) 1mA × C1 + 44 pF × 6.7 kΩ
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
FOUT FS
( ) C2 =
10–4 Farads / sec
F OUT FS
1000 pF minimum
VIN FS
RIN = 0.25 mA
R2 ≥
+VLOGIC
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.
VIN FS
1V
10 V
1V
10 V
Table I. Suggested Values for C1, RIN and C2
FOUT FS
10 kHz
10 kHz
100 kHz
100 kHz
C1
3650 pF
3650 pF
330 pF
330 pF
RIN
4.0 kΩ
40 kΩ
4.0 kΩ
40 kΩ
C2
0.01 µF
0.01 µF
1000 pF
1000 pF
ORDERING GUIDE
Part
Number1
Gain Tempco Temp Range Package
ppm/؇C
؇C
Option
ADVFC32KN ± 75 typ
0 to 70
14-Pin
Plastic DIP
Figure 2. Voltage-to-Frequency Conversion Waveforms
ADVFC32BH
ADVFC32SH
± 100 max
± 150 max
–25 to +85 TO-100
–55 to +125 TO-100
During this period, a current of (1 mA – IIN) flows out of the
integration capacitor. The total amount of charge depleted
during one cycle is, therefore (1 mA – IIN) × tOS. This charge is
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.
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
recommended to avoid performance degradation or loss of functionality.
ESD SENSITIVE DEVICE
REV. B
–3–
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