FUJITSU SEMICONDUCTOR
DATA SHEET
DS04-27402-4E
ASSP
POWER-VOLTAGE MONITORING IC
WITH WATCHDOG TIMER
MB3793-42
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 fail-safe function for various application systems.
There is also a mask option that can detect voltages of 4.9 to 2.4V in 0.1-V steps.
The model number and package code are as shown below.
Model No.
MB3793-42
Package code
3793-A
Detection voltage
4.2 V
s
FEATURES
•
•
•
•
•
•
•
Precise detection of power voltage fall:
±2.5%
Detection voltage with hysteresis
Low power dispersion: I
CC
= 27
µA
(reference)
Internal dual-input watchdog timer
Watchdog timer halt function (by inhibition terminal)
Independently-set watchdog and reset times
Mask option for detection voltage (4.9 to 2.4 V, 0.1-V steps)
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PACKAGES
8-pin plastic DIP
8-pin plastic SOP
8-pin plastic SOP
(DIP-8P-M01)
(FPT-8P-M01)
(FPT-8P-M02)
MB3793-42
s
PIN ASSIGNMENT
(TOP VIEW)
1
2
3
4
8
7
6
5
CK1
CK2
INH
V
CC
RESET
CTW
CTP
GND
(DIP-8P-M01)
(FPT-8P-M01)
(FPT-8P-M02)
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PIN DESCRIPTION
Pin No.
1
2
3
4
Symbol
RESET
CTW
CTP
GND
Description
Outputs reset
Sets monitoring time
Sets power-on reset hold time
Ground
Pin No.
5
6
7
8
Symbol
V
CC
INH
CK2
CK1
Description
Power supply
Inhibits watchdog timer function
Inputs clock 2
Inputs clock 1
2
MB3793-42
s
BLOCK DIAGRAM
To V
CC
of all blocks
I
1
≅
3
µA
I
2
≅
30
µA
5
V
CC
CTP
3
Q
S
R
1
≅
590 kΩ
Output
buffer
RESET
1
RSFF2
Comp. O
+
−
Q
R
Q
S
RSFF1
Q
INH
6
R
Comp. S
CTW
2
Watchdog
timer
Pulse generator 1
Reference
voltage
generator
−
+
V
S
CK1
8
V
REF
≅
1.24 V
R
2
≅
240 kΩ
Pulse generator 2
CK2
7
To GND of all blocks
4
GND
3
MB3793-42
s
BLOCK FUNCTIONS
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 R
1
and R
2
. When V
S
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
(C
TP
). The flip-flop circuit RSFF2 switches the charging accelerator for charging C
TP
during resetting on/off. This
circuit only functions during resetting and does not function at power-on reset.
4
MB3793-42
s
ABSOLUTE MAXIMUM RATINGS
(Ta =
+25°C)
Parameter
Power voltage*
CK1
Input voltage*
CK2
INH
Reset output voltage
(direct current)
RESET
Symbol
V
CC
V
CK1
V
CK2
V
INH
I
OL
I
OH
P
D
Tstg
−10
−55
+10
200
+125
mA
mW
°C
−0.3
+7
V
Rating
Min
−0.3
Max
+7
Unit
V
Power dissipation (Ta
≤
+85°C)
Storage temperature
*: The power 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
Watchdog timer monitoring time
Operating ambient temperature
Symbol
V
CC
I
OL
I
OH
C
TP
C
TW
t
WD
Ta
Value
Min
1.2
−5
0.001
0.001
0.1
−40
Typ
5.0
0.1
0.1
+25
Max
6.0
+5
10
1
1500
+85
Unit
V
mA
µF
µF
ms
°C
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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