FUJITSU SEMICONDUCTOR
DATA SHEET
DS04-27404-1E
ASSP For Power Supply Applications
BIPOLAR
Power Voltage Monitoring IC
with Watchdog Timer
MB3793
-27A
s
DESCRIPTION
The MB3793 is an integrated circuit to monitor power voltage; it incorporates a watchdog timer.
A reset signal is output when the power is cut or falls abruptly. When the power recovers normally after resetting,
a power-on reset signal is output to microprocessor units (MPUs). An internal watchdog timer with two inputs for
system operation diagnosis can provide a fall-safe function for various applicaiton systems.
There is also a mask option that can detect voltages of 4.9 to 2.4 V in 0.1-V steps.
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FEATURES
•
•
•
•
•
•
Precise detection of power voltage fall:
±2.5%
Detection voltage with hysteresis
Low power dispersion: I
CC
= 31
µA
(reference)
Internal dual-input watchdog timer
Watchdog-timer halt function (by inhibition pin)
Independently-set wacthdog and reset times
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PACKAGE
8-pin, Plastic SOP
8-pin, Plastic SOL
(FPT-8P-M01)
8-pin, Plastic SSOP
(FPT-8P-M02)
8-pin, Plastic DIP
(FPT-8P-M03)
(DIP-8P-M01)
MB3793
-27A
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PIN ASSIGNMENT
(TOP VIEW)
1
2
3
4
8
7
6
5
CK1
CK2
INH
V
CC
RESET
CTW
CTP
GND
(FPT-8P-M01)
(FPT-8P-M02)
(FPT-8P-M03)
(DIP-8P-M01)
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PIN DESCRIPTION
Pin no.
1
2
3
4
Symbol
RESET
CTW
CTP
GND
Descriptions
Outputs reset pin
Watchdog timer monitor time
setting pin
Power-on reset hold time
setting pin
Ground pin
Pin no.
5
6
7
8
Symbol
V
CC
INH
CK2
CK1
Descriptions
Power supply pin
Inhibit pin
Inputs clock 2 pin
Inputs clock 1 pin
2
MB3793
-27A
s
BLOCK DIAGRAM
To V
CC
of all blocks
.
I
1
= 3
µA
.
=
I
2
. .
30
µA
5 V
CC
CTP 3
.
R
1
=
.
295 kΩ
RESET 1
Output circuit
Logic circuit
INH 6
Comp.S
CTW 2
Pulse generator 1
CK1 8
.
V
REF
= 1.24 V
.
R
2
. .
=
240 kΩ
To GND of
all blocks
Watchdog
timer
Reference
voltage
generator
−
+
V
S
Pulse generator 2
CK2 7
4 GND
3
MB3793
-27A
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BLOCK DESCRIPTION
1. Comp. S
Comp. S is a comparator with hysteresis to compare the reference voltage with a voltage (V
S
) that is the result of
dividing the power voltage (V
CC
) by resistors 1 and 2. When V
S
falls below 1.24 V, a reset signal is output.
This function enables the MB3793 to detect an abnomality within 1
µs
when the power is cut or falls abruptly.
2. Output circuit
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.
3. Pulse generator
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.
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
The logic circuit contains flip-flops.
Flip-flop RSFF1 controls the charging and discharging of the power-on reset time setting capacitor (C
TP
).
Flip-flop RSFF2 turns on/off the circuit that accelerates charging of the power-on reset time setting capacitor
(C
TP
) at a reset. The RSFF2 operates only at a reset; it does not operate at a power-on reset when the power is
turned on.
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MB3793
-27A
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ABSOLUTE MAXIMUM RATINGS
(Ta = +25°C)
Parameter
Power supply voltage*
CK1
Input voltage*
CK2
INH
Reset output current
Power dissipation
Storage temperature
RESET
Symbol
V
CC
V
CK1
V
CK2
I
INH
I
OL
I
OH
P
D
Tstg
Conditions
—
—
—
—
—
Ta
≤
+85°C
—
–10
—
–55
+10
200
+125
mA
mW
°C
–0.3
+7
V
Rating
Min.
–0.3
Max.
+7
Unit
V
* : The voltage is based on the ground voltage (0 V).
WARNING: Semiconductor devices can be permanently damaged by application of stress (voltage, current,
temperature, etc.) in excess of absolute maximum ratings. Do not exceed these ratings.
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RECOMMENDED OPERATING CONDITIONS
Parameter
Power supply voltage
Reset (RESET) output current
Power-on reset hold time setting
capacity
Watchdog-timer monitoring time
setting capacity
Operating temperature
Symbol
V
CC
I
OL
I
OH
C
TP
C
TW
Ta
Conditions
—
—
—
—
—
Value
Min.
1.2
–5
0.001
0.001
–40
Typ.
—
—
—
—
—
Max.
6.0
+5
10
1
+85
Unit
V
mA
µF
µF
°C
* : The watchdog timer monitor time range depends on the rating of the setting capacitor.
WARNING: The recommended operating conditions are required in order to ensure the normal operation of the
semiconductor device. All of the device's electrical characteristics are warranted when the device is
operated within these ranges.
Always use semiconductor devices within their recommended operating condition ranges. Operation
outside these ranges may adversely affect reliability and could result in device failure.
No warranty is made with respect to uses, operating conditions, or combinations not represented on
the data sheet. Users considering application outside the listed conditions are advised to contact their
FUJITSU representatives beforehand.
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