VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
1
2
3
4
5
6
7
8
TC9400
TC9401
TC9402
In some cases, however, the TC9400 output must be
zero at power-on without a frequency input. In such cases,
a capacitor connected from pin 11 to VDD will usually be
sufficient to pulse the TC9400 and provide a power-on reset
(see Figure 11A). Where predictable power-on operation is
critical, a more complicated circuit, such as Figure 11B, may
be required.
F/V POWER-ON RESET
In F/V mode, the TC9400 output voltage will occasion-
allybeatitsmaximumvaluewhenpowerisfirstapplied.This
conditionremainsuntilthefirstpulseisappliedtofIN. Inmost
frequency-measurement applications this is not a problem,
because proper operation begins as soon as the frequency
input is applied.
V
DD
14
1000pF
1kΩ
THRESHOLD
DETECTOR
11
f
IN
(A)
TC9400
V
DD
(B)
16
5
2
1
V
B
R
C
CC
3
4
CLRA
100kΩ
1µF
CD4538
6
Q
To TC 9400
A
V
SS
f
IN
8
Figure 11. Power-On Operation/Reset
TELCOM SEMICONDUCTOR, INC.
3-299
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
