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
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,
–
t
OS
(1 mA – I
IN
)
×
t
OS
= I
IN
×
F
OUT
1
or, rearranging terms,
F
OUT
=
I
IN
1
mA
×
t
OS
The complete transfer equation can now be derived by substi-
tuting I
IN
= V
IN
/R
IN
and the equation relating C1 and t
OS
. The
final equation describing ADVFC32 operation is:
V
II
/
R
IN
N
1mA
×
C
1
+
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
×10
7
pF
/
sec
– 44
pF
F
OUT FS
10
–4
Farads
/
sec
1000
pF minimum
C
2
=
F
OUT FS
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 t
1
), the
comparator triggers a one shot whose time period is determined
R
IN
=
R
2
≥
V
IN FS
0.25
mA
+V
LOGIC
8
mA
Both R
IN
and C
1
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.
Table I. Suggested Values for C
1
, R
IN
and C
2
V
IN FS
1V
10 V
1V
10 V
F
OUT FS
10 kHz
10 kHz
100 kHz
100 kHz
C
1
3650 pF
3650 pF
330 pF
330 pF
R
IN
4.0 kΩ
40 kΩ
4.0 kΩ
40 kΩ
C
2
0.01
µF
0.01
µF
1000 pF
1000 pF
ORDERING GUIDE
Part
Number
1
Gain Tempco
ppm/ C
±
75 typ
±
100 max
±
150 max
Temp Range
C
0 to +70
–25 to +85
–55 to +125
Package
Option
14-Pin
Plastic DIP
TO-100
TO-100
Figure 2. Voltage-to-Frequency Conversion Waveforms
by capacitor C1. Specifically, the one shot time period (in nano-
seconds) is:
t
OS
≅
(C
l
+ 44
pF)
×
6.7
kΩ
During this period, a current of (1 mA – I
IN
) flows out of the in-
tegration capacitor. The total amount of charge depleted during
one cycle is, therefore (1 mA – I
IN
)
×
t
OS
. This charge is replaced
ADVFC32KN
ADVFC32BH
ADVFC32SH
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.
NOTE
1
For 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.
WARNING!
ESD SENSITIVE DEVICE
REV. A
–3–
AD [ ANALOG DEVICES ]
