mm1407 Mitsumi Electronics, Corp., mm1407 Datasheet - Page 10

• Manufacturer Part Number: mm1407
• Description: Monolithic Ic Mm1407
• Manufacturer: Mitsumi Electronics, Corp.

Figure C. Watchdog Timer
Basically, the watchdog timer monitors the level (3) of the current it impresses on the external capacitor. The
charging time is determined by C1 and I2 in the block diagram, and control is done by input signal (1). When
the first "H" trigger (input signal) chargers the external capacitor and level (3) goes over (4) "H" threshold
value, output is first inverted (L
charging current impress/stop to the external capacitor, but if input signal (1) is not impressed within the set
time (clock monitoring time), charging to the external capacitors is stopped and the capacitor starts discharge
operation. Then level (3) falls below "L" threshold value and output (5) is again inverted (H
1. WAKEUP pin input signal cycle limit
2. WAKEUP pin input signal amplitude limit
3. External capacitor time constant (sets clock monitoring time)
Use at 1/Ta or higher, 100Hz or lower.
T1: clock monitoring time (The time from WAKEUP signal input stop until logic truth table WAKEUP
switches to low.)
Use at 1.5V or higher, 5V or lower.
Determined by T1 = 1.638
(E.g.: If C = 1µF, for T1 . = . 1S, R = 620kΩ, for T1 . = . 2S, R = 1.2MΩ)
C µF
H). While the input signal is being continuously impressed, the timer repeats
Watchdog Timer Circuit Block Diagram
R [Ω].
L).