MB3793-27A Datasheet, PDF (11/25 Pages) Fujitsu Component Limited. – Power Voltage Monitoring IC with Watchdog Timer

5. Clock pulse input supplementation (Positive clock pulse)
MB3793-27A
*1
CK1
*2
CK2
VH
CTW
VL
Note : The MB3793 watchdog timer monitors Clock1 (CK1) and Clock2 (CK2) pulses alternately.
When a CK2 pulse is detected after detecting a CK1 pulse, the monitoring time setting capacity (CTW)
switches to charging from discharging.
When two consecutive pulses occur on one side of this alternation before switching, the second pulse
is ignored.
In the above figure, pulse *1 and *2 are ignored.
■ OPERATION SEQUENCE
1. Positive clock pulse input
See “1. Basic operation (positive clock pulse)” under “■ DIAGRAM.”
2. Negative clock pulse input
See “2. Basic operation (negative clock pulse)” under “■ DIAGRAM.”
The MB3793 operates in the same way whether it inputs positive or negative pulses.
3. Clock monitoring
To use the MB3793 while monitoring only one clock, connect clock pins CK1 and CK2.
Although the MB3793 operates basically in the same way as when monitoring two clocks, it monitors the clock
signal at every other input pulse.
See “3. Single-clock input monitoring (positive clock pulse)” under “■ DIAGRAM.”
4. Description of Operations
The numbers given to the following items correspond to numbers (1) to (13) used in “■ DIAGRAM.”
(1) The MB3793 outputs a reset signal when the supply voltage (VCC) reaches about 0.8 V (VCCL)
(2) If VCC reaches or exceeds the rise-time detected voltage VSH, the MB3793 starts charging the power-on
reset hold time setting capacitor CTP. At this time, the output remains in a reset state. The VSH value is about
2.76 V.
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