VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
TC9400
TC9401
TC9402
+
V
= 10V to 15V
14
10k
VDD
6
GND
.01µF
6.2V
10k
TC9400
5
3
V
REFOUT
500k
ZERO
ADJUST
2
47pF
100k
+
V
IIN
Offset
Adjust
.001µF
1M
12
6
AMP OUT
GND
1.0k
0.01µF
33k
Frequency
Input
11
VOUT
DET
IN914
IBIAS
1.0M
VREF
VSS
4
7
0.1µF
1.0k
100k
Note: The output is referenced to pin 6, which is at 6.2V (Vz). For frequency meter applications,
a 1 mA meter with a series-scaling resistor can be placed across pins 6 and 12.
Figure 9. F/V Single Supply F/V Converter
Output Filtering
The output of the TC9400 has a sawtooth ripple super-
imposed on a DC level. The ripple will be rejected if the
TC9400 output is converted to a digital value by an integrat-
ing analog to digital converter, such as the TC7107 or
TC7109. The ripple can also be reduced by increasing the
value of the integrating capacitor, although this will reduce
the response time of the F/V converter.
5
3
V
REFOUT
47pF
IIN
TC9400
.001µF
200
1M
12
AMP OUT
The sawtooth ripple on the output of an F/V can be
eliminated without affecting the F/V's response time by
using the circuit in Figure 10. The circuit is a capacitance
multiplier, where the output coupling capacitor is multiplied
by the AC gain of the op amp. A moderately fast op amp,
such as the TL071, should be used.
0.1µF
1M
.01µF
GND
6
+5
VOUT
7
4
2
3
–
+
6
TL071
1M
–5
Figure 10. Ripple Filter
3-298
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
