TC9400_06 Datasheet, PDF (18/24 Pages) Microchip Technology – Voltage-to-Frequency/Frequency-to-Voltage Converters

TC9400/9401/9402
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. In most frequency measurement appli-
cations, this is not a problem because proper operation
begins as soon as the frequency input is applied.
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 V_DD will
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
complicated circuit, such as Figure 8-1 (b), may be
required.
F_IN
1 kΩ
(a)
V_DD
14
1000 pF
11 Threshold
Detector
V_DD
100 kΩ
TC9400
1 μF
16
3 ^VCC
CLRA
4A
(b)
5
2
B
R
CD4538
V_SS
8
1
C
6
Q
F_IN
To TC9400
FIGURE 8-1:
Power-On Operation/Reset
DS21483C-page 18
© 2006 Microchip Technology Inc.