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MB3773 Datasheet, PDF (5/31 Pages) Fujitsu Component Limited. – Power Supply Monitor with Watch-Dog Timer
MB3773
3. Functional Descriptions
Comp.S is comparator including hysteresis. it compare the reference voltage and the voltage of Vs, so that when the voltage of Vs
terminal falls below approximately 1.23 V, reset signal outputs.
Instantaneous breaks or drops in the power can be detected as abnormal conditions by the MB3773 within a 2 μs interval.
However because momentary breaks or drops of this duration do not cause problems in actual systems in some cases, a delayed
trigger function can be created by connecting capacitors to the Vs terminal.
Comp.O is comparator for turning on/off the output and, compare the voltage of the CT terminal and the threshold voltage. Because
the RESET/RESET outputs have built-in pull-up circuit, there is no need to connect to external pull-up resistor when connected to a
high impedance load such as CMOS logic IC.
(It corresponds to 500 kΩ at Vcc = 5 V.) when the voltage of the CK terminal changes from the “high” level into the “Low” level, pulse
generator is sent to the watch-dog timer by generating the pulse momentarily at the time of drop from the threshold level.
When power-supply voltages fall more than detecting voltages, the watch-dog timer becomes an interdiction.
The Reference amplifier is an op-amp to output the reference voltage.
If the comparator is put up outside, two or more power-supply voltage monitor and overvoltage monitor can be done.
If it uses a comparator of the open-collector output, and the output of the comparator is connected with the Vs terminal of MB3773
without the pull-up resistor, it is possible to voltage monitor with reset-hold time.
Document Number: 002-08513 Rev. *A
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