TC9400/9401/9402
In some cases, however, the TC9400 output must be
zero at power-on without a frequency input. In such
8.0
F/V POWER-ON RESET
In F/V mode, the TC9400 output voltage will occasion-
ally be at its maximum value when power is first
applied. This condition remains until the first pulse is
applied to F . In most frequency measurement appli-
cations, this is not a problem because proper operation
begins as soon as the frequency input is applied.
cases, a capacitor connected from Pin 11 to V
will
DD
usually be sufficient to pulse the TC9400 and provide a
Power-on Reset (see Figure 8-1 (a) and (b)). Where
predictable power-on operation is critical, a more com-
plicated circuit, such as Figure 8-1 (b), may be
required.
IN
FIGURE 8-1:
POWER-ON OPERATION/RESET
(a)
(b)
V
DD
V
DD
14
16
5
2
1
1000pF
V
B
R
C
CC
3
4
CLRA
1kΩ
F
IN
Threshold
Detector
11
100kΩ
1µF
CD4538
6
To TC9400
Q
A
V
SS
F
IN
TC9400
8
2002 Microchip Technology Inc.
DS21483B-page 15
MICROCHIP [ MICROCHIP ]
