HA16103 Datasheet, PDF (7/21 Pages) Hitachi Semiconductor – Watchdog Timer

HA16103 FPJ/FPK
Watchdog Timer Function
The system contains a bandpass filter for pulse width detection, which outputs a reset pulse when input
pulses are not at the preselected frequency (at either a higher or lower frequency).
The RC characteristic of the bandpass filter may be set with external components Rf and Cf. Equation 3
specifies how to determine the minimum pulse width (tmin) for runaway detection of the bandpass filter,
and figure 4 shows the characteristic of the filter.
HA16103
Rf Cf
tmin = Cf x Rf x 0.11 (s) ⋅ ⋅ ⋅ ⋅ Equation 3
Rf : Ω
2.0 m
1.8 m
1.6 m
1.4 m
1.2 m
1.0 m
0.8 m
0.6 m
0.4 m
0.2 m
100 k
(Ta = 25°C)
P—Run pulse duty ratio 50% (fixed)
V_CC = 12 V
C_R = 0.1 µF
R_R = 180 k Ω
Cf = 0.022 µF
Cf = 0.01 µF
Cf = 0.0047 µF
200 k
500 k
Resistance Rf (Ω)
Figure 4 Characteristic of Power-On Reset Circuit
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