Spansion
®
Analog and Microcontroller
Products
The following document contains information on Spansion analog and microcontroller products. Although the
document is marked with the name “Fujitsu”, the company that originally developed the specification, Spansion
will continue to offer these products to new and existing customers.
Continuity of Specifications
There is no change to this document as a result of offering the device as a Spansion product. Any changes that
have been made are the result of normal document improvements and are noted in the document revision
summary, where supported. Future routine revisions will occur when appropriate, and changes will be noted in a
revision summary.
Continuity of Ordering Part Numbers
Spansion continues to support existing part numbers beginning with “MB”. To order these products, please use
only the Ordering Part Numbers listed in this document.
For More Information
Please contact your local sales office for additional information about Spansion memory, analog, and
microcontroller products and solutions.
FUJITSU MICROELECTRONICS
DATA SHEET
DS04-27404-3Ea
ASSP For Power Supply Applications
BIPOLAR
Power Voltage Monitoring IC
with Watchdog Timer
MB3793
-27A
■
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 application systems.
There is also a mask option that can detect voltages of 4.9 to 2.4 V in 0.1-V steps.
■
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
Three types of packages (SOP-8pin : 2 types, SSOP-8pin : 1 type)
■
APPLICATION
• Arcade Amusement
etc.
Copyright©1992-2008 FUJITSU MICROELECTRONICS LIMITED All rights reserved
2006.5
MB3793
-27A
■
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)
■
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
■
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
■
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 hold time setting capacitor (C
TP
).
Flip-flop RSFF2 turns on/off the circuit that accelerates charging of the power-on reset hold 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.
4
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EEWORLD
