FUJITSU MICROELECTRONICS
DATA SHEET
DS04-27405-2E
ASSP
BIPOLAR
POWER-VOLTAGE MONITORING IC
WITH WATCHDOG TIMER
MB3793-45
■
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.
Model No.
MB3793-45
Marking Code
3793-7
Detection voltage
4.5 V
■
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 watchdog and reset times
■
APPLICATION
• Arcade Amusement
etc.
Copyright©2000-2009 FUJITSU MICROELECTRONICS LIMITED All rights reserved
2009.9
MB3793-45
■
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)
■
PIN DESCRIPTION
Pin No.
1
2
3
4
5
6
7
8
Symbol
RESET
CTW
CTP
GND
V
CC
INH
CK2
CK1
Outputs reset
Sets monitoring time
Sets power-on reset hold time
Ground
Power supply
Inhibits watchdog timer function
Inputs clock 2
Inputs clock 1
Description
2
DS04-27405-2E
MB3793-45
■
BLOCK DIAGRAM
To V
CC
of all blocks
.
I
1
= 3
μA
.
I
2
. .
30
μA
=
5 V
CC
CTP 3
.
R
1
=
.
650 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
DS04-27405-2E
3
MB3793-45
■
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. 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 (C
TP
) on a signal
of Comp.S and Watchdog timer.
4
DS04-27405-2E
MB3793-45
■
ABSOLUTE MAXIMUM RATINGS
Parameter
Power supply voltage*
CK1
Input voltage*
CK2
INH
Reset output voltage*
RESET
Reset output current
Power dissipation
Storage temperature
Symbol
V
CC
V
CK1
V
CK2
I
INH
V
OL
V
OH
I
OL
I
OH
P
D
Tstg
Conditions
⎯
⎯
⎯
⎯
⎯
⎯
Ta
≤ +85 °C
⎯
−0.3
−10
⎯
−55
−0.3
Rating
Min
−0.3
Max
+7
V
CC
+
0.3
(
≤ +7)
V
CC
+
0.3
(
≤ +7)
+10
200
+125
Unit
V
V
V
mA
mW
°C
* : 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.
■
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 ambient temperature
Symbol
V
CC
I
OL
I
OH
C
TP
C
TW
Ta
Conditions
⎯
⎯
⎯
⎯
⎯
⎯
Value
Min
1.2
0
−5
0.001
0.001
−40
Typ
5.0
—
—
0.1
0.01
+25
Max
6.0
+
5
0
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 representatives beforehand.
DS04-27405-2E
5
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