MB3793-42PNF-G Datasheet, PDF (4/23 Pages) Fujitsu Component Limited. – POWER-VOLTAGE MONITORING IC WITH WATCHDOG TIMER

MB3793-42
s 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. Comp. O
Comp. O is a comparator to control the reset signal (RESET) output and compares the threshold voltage with
the voltage at the CTP terminal for setting the power-on reset hold time. When the voltage at the CTP terminal
exceeds the threshold voltage, resetting is canceled.
3. Reset output buffer
Since the reset (RESET) output buffer has CMOS organization, no pull-up resistor is needed.
4. Pulse generator
The pulse generator generates pulses when the voltage at the CK1 and CK2 clock terminals changes to High
from Low level (positive-edge trigger) and exceeds the threshold voltage; it sends the clock signal to the watchdog
timer.
5. Watchdog timer
The watchdog timer can monitor two clock pulses. Short-circuit the CK1 and CK2 clock terminals to monitor a
single clock pulse.
6. Inhibition terminal
The inhibition (INH) terminal forces the watchdog timer on/off. When this terminal is High level, the watchdog
timer is stopped.
7. Flip-flop circuit
The flip-flop circuit RSFF1 controls charging and discharging of the power-on reset hold time setting capacity
(CTP). The flip-flop circuit RSFF2 switches the charging accelerator for charging CTP during resetting on/off. This
circuit only functions during resetting and does not function at power-on reset.
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