MB3793-30A Fujitsu Media Devices, MB3793-30A Datasheet - Page 4

• Manufacturer Part Number: MB3793-30A
• Description: POWER-VOLTAGE MONITORING IC WITH WATCHDOG TIMER
• Manufacturer: Fujitsu Media Devices

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DataSheet
4
4
MB3793
1. Comp. S
2. Output circuit
3. Pulse generator
4. Watchdog timer
5. Inhibition pin
6. Logic circuit
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BLOCK DESCRIPTION
Comp. S is a comparator with hysteresis to compare the reference voltage with a voltage (V
of dividing the power voltage (V
This function enables the MB3793 to detect an abnormality when the power is cut or falls abruptly.
The output circuit contains a RESET output control comparator that compares the voltage at the CTP pin to the
threshold voltage to release the RESET output if the CTP pin voltage exceeds the threshold value.
Since the reset (RESET) output buffer has CMOS organization, no pull-up resistor is needed.
The pulse generator generates pulses when the voltage at the CK1 and CK2 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.
The watchdog timer can monitor two clock pulses. Short-circuit the CK1 and CK2 clock pins to monitor a single
clock pulse.
The inhibition (INH) pin forces the watchdog timer on/off. When this pin is High level, the watchdog timer is
stopped.
The logic circuit contains flip-flops.
Flip-flop RSFF1 controls the charging and discharging of the power-on reset time setting capacitor (C
Flip-flop RSFF2 turns on/off the circuit that accelerates charging of the power-on reset time setting capacitor
(C
is turned on.
TP
) at a reset. The RSFF2 operates only at a reset; it does not operate at a power-on reset when the power
-30A
CC
) by resistors 1 and 2. When V
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S
falls below 1.24 V, a reset signal is output.
S
) that is the result
TP
).