DS04-27401-8E
FUJITSU SEMICONDUCTOR
DATA SHEET
Copyright2003-2006 FUJITSU LIMITED All rights reserved
ASSP
BIPOLAR
Power Supply Monitor
with Watch-Dog Timer
MB3773
DESCRIPTION
MB3773 generates the reset signal to protect an arbitrary system when the power-supply voltage momentarily is
intercepted or decreased. It is IC for the power-supply voltage watch and "Power on reset" is generated at the
normal return of the power supply. MB3773 sends the microprocessor the reset signal when decreasing more
than the voltage, which the power supply of the system specified, and the computer data is protected from an
accidental deletion.
In addition, the watch-dog timer for the operation diagnosis of the system is built into, and various microprocessor
systems can provide the fail-safe function. If MB3773 does not receive the clock pulse from the processor for a
specified period, MB3773 generates the reset signal.
FEATURES
Precision voltage detection (V
S
= 4.2 V
2.5 %)
Detection threshold voltage has hysteresis function
Low voltage output for reset signal (V
CC
= 0.8 V Typ)
Precision reference voltage output (V
R
= 1.245 V
1.5%)
With built-in watch-dog timer of edge trigger input.
External parts are few.(1 piece in capacity)
The reset signal outputs the positive and negative both theories reason.
One type of package (SOP-8pin : 1 type)
APPLICATION
Industrial Equipment
Arcade Amusement etc.
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
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 C
T
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
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.
PDF 
ZIP
