FUJITSU MB3773 - Manual (Page 4)

MB3773
4
■ ■ ■ ■ 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
µ
s 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 Cr 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 k
Ω
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 a interdiction.
The Reference amplifier is a 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.