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PRODUCT SPECIFICATION
RC4152
8
The input waveform must have fast slewing edges, and the
differentiated input signal must be less than the timing
period of the one-shot, 1.1 R
O
C
O
. A differentiator and
divider are used to shape and bias the trigger input; a nega-
tive going pulse at pin 6 will cause the comparator to fire the
one-shot. The input pulse amplitude must be large enough to
trip the comparator, but not so large as to exceed the ICs
input voltage ratings.
The output voltage is directly proportional to the input
frequency:
Output ripple can be minimized by increasing CB, but this
will limit the response time. Recommended values for
various operating ranges are shown in the following table.
Precision FVC
Linearity, offset and response time can be improved by
adding one or more op amps to form an active lowpass filter
at the output. A circuit using a single pole active integrator is
shown in Figure 5.
The positive output current pulses are averaged by the invert-
ing integrator, causing the output voltage to be negative.
Response time can be further improved by adding a double
pole filter to replace the single pole filter. Refer to the graphs
under Typical Performance Characteristics that show
nonlinearity error versus input frequency for the
precision FVC circuit.
Input
Operating
Rage
C
IN
R
O
C
O
R
B
C
B
Ripple
0 to 1.0 kHz
0.02
m
F
0.002
m
F 6.8 k
W
0.01
m
F
200 pF
6.8 k
W
0.001
m
F 100 k
W
6.8 k
W
0.1
m
F
100 k
W
100 k
W
100
m
F 1.0 mV
10
m
F
1.0
m
F
0 to 10 kHz
1.0 mV
0 to 100 kHz
1.0 mV
V
OUT
1.1R
C
R
V
S
-------------------R
IN
Hz
(
)
=
Figure 4. Single Supply FVC
4152-07
+15V
10 k
W
10 k
W
C
0.022 F
R
6.8 k
OUT
S
2
W
7
V
IN
TH
S
OUT
1
OUT
V
+V
I
C
O
4152
VFC
Gnd
F
R
O
3
4
5
8
C
0.01 F
O
R = 16.7K
6
C
10 F
B
m
V
R
100K
+15V
5 k
W
10 k
W
Frequency
Input
0 F 10kHz
F
IN