MB3793-45 Datasheet, PDF (4/28 Pages) Fujitsu Component Limited. – POWER-VOLTAGE MONITORING IC WITH WATCHDOG TIMER

MB3793-45
■ BLOCK FUNCTIONS
1. Comp. S
Comp. S is a comparator with hysteresis to compare the reference voltage with a voltage (VS) that is the result
of dividing the power voltage (VCC) by resistors R1 and R2. When VS falls below 1.24 V, a reset signal is output.
This function enables the MB3793 to detect an abnormality within 1 μs when the power is cut or falls abruptly.
2. Output circuit
The output circuit has a comparator to control the reset signal (RESET) output. When the voltage at the CTP
pin for setting the power-on reset hold time exceeds the threshold voltage, resetting is canceled.
Since the reset (RESET) output buffer has the CMOS organization, no pull-up resistor is needed.
3. Pulse generator
The pulse generator generates pulses when the voltage at the CK1 and CK2 input clock pins changes to High
from Low level (positive-edge trigger) and exceeds the threshold voltage; it sends the clock signal to the watchdog
timer.
4. Watchdog timer
The watchdog timer can monitor two clock pulses. Short-circuit the CK1 and CK2 clock pins to monitor a single
clock pulse.
5. Inhibition pin
The inhibition (INH) pin forces the watchdog timer on/off. When this pin is High level, the watchdog timer is
stopped.
6. Logic circuit
Logic circuit controls charging and discharging of the power-on reset hold time setting capacity (CTP) on a signal
of Comp.S and Watchdog timer.
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DS04-27405-2E