HA16117F Datasheet, PDF (16/31 Pages) Hitachi Semiconductor – CMOS Watchdog Timer

HA16117F Series
Setting of RES Timing and Watchdog Frequency Range
Different MPUs have different RES timing requirements. The minimum reset time (t_ON) required at power-
on (rise of V_CC) is 20 ms for some MPUs and 100 ms for others.
RES timing waveform parameters must be selected according to the MPU. With the HA16117F the timing
of the RES output and the watchdog frequency range can both be set by external constants (C_F, C_R, and K).
Parameters
Item
Symbol
CR (pin 4)
CF (pin 3)
K (pin 8) *¹
Power-on reset time
t _ON
q
Reset-clock off time
t _OFF
q
v *²
q
Reset low time
t _RL
q
Reset high time
t _RH
q
q
Watchdog frequency high f_H
q
q
Watchdog frequency low
f_L
q
q
q
Notes: 1. K = R₂ / (R₁ + R₂)
2. Variability of t_OFF increases with increasing C_F. The variability ∆t_OFF is approximately
3.3 (MΩ) × C_F (µF), so C_F ≤ 0.01 (µF) is recommended.
3. External constants should be selected with reference to the formulas in tables 1 and 2.
Table 1
Item
t_ON (ms)
t_OFF (ms)
t_RL (ms)
t_RH (ms)
t_SL (ms)
Calculation of RES Output Timing
Formula
400 (Ω) × C_R (µF)
1.99 × t_RH (ms)
0.5 × t_ON (ms)
K
×
31
1.6
(µA)
(V)
− 15.8
(µA)
×
C_R
(µF)
×
10³
≈ t_OFF (ms)
Notes
t_ON and t_OFF can be set independently
t_RL and t_RH can be set independently
Table 2
Item
f_H (MHz)
f_L (Hz)
Calculation of Watchdog Frequency Range
Formula
1
500 (Ω) × C_F (µF)
×
t_RH (ms) − t_RL (ms)
t_RH (ms) + t_RL (ms)
1
1.7 (MΩ) × C_F (µF)
×
t_RL (ms)
t_RH (ms) + t_RL (ms)
or
1
t_OFF (ms)
× 10³
Whichever is larger
16