DS1233
5V EconoReset
www.maxim-ic.com
FEATURES
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Automatically restarts microprocessor after
power failure
Monitors pushbutton for external override
Internal circuitry debounces pushbutton
switch
Maintains reset for 350ms after V
CC
returns to
an in-tolerance condition or pushbutton
released
Accurate 5%, 10%, or 15% microprocessor
5V power supply monitoring
Reduces need for discrete components
Precision temperature-compensated voltage
reference and voltage sensor
Low-cost TO-92 package or surface-mount
SOT-223 package
Internal 5kW pull-up resistor
Operating temperature of -40°C to +85°C
PIN ASSIGNMENT
DALLAS
DS1233
Econo
Reset
1
1 2 3
1 2 3
BOTTOM VIEW
TO-92 PACKAGE
See Mech.
Drawings Section
on Website
2 4 3
TOP VIEW
SOT-223 PACKAGE
See Mech.
Drawings Section
on Website
PIN DESCRIPTION
PIN 1
PIN 2
PIN 3
PIN 4
GROUND
RESET
V
CC
GROUND (SOT-223 ONLY)
DESCRIPTION
The DS1233 EconoReset monitors two vital conditions for a microprocessor: power supply and external
override. A precision temperature-compensated reference and comparator circuit are used to monitor the
status of the power supply (V
CC
). When an out-of-tolerance condition is detected, an internal power-fail
signal is generated which forces reset to the active state. When V
CC
returns to an in-tolerance condition,
the reset signal is kept in the active state for approximately 350ms to allow the power supply and
processor to stabilize. The second function of the DS1233 is pushbutton reset control. The DS1233
debounces a pushbutton closure and will generate a 350ms reset pulse upon release.
OPERATION — POWER MONITOR
The DS1233 provides the functions of detecting out-of-tolerance power supply conditions and warning a
processor-based system of impending power failure. When V
CC
is detected as out-of-tolerance, as
defined by the tolerance of the part selected, the
RST
signal is asserted. On power-up,
RST
is kept active
for approximately 350ms after the power supply has reached the selected tolerance. This allows the power
supply and microprocessor to stabilize before
RST
is released.
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122001
DS1233
OPERATION — PUSHBUTTON RESET
The DS1233 provides for a pushbutton switch to be connected to the
RST
output pin. When the DS1233
is not in a reset cycle, it continuously monitors the
RST
signal for a low going edge. If an edge is
detected, the DS1233 will debounce the switch by pulling the
RST
line low. After the internal timer has
expired, the DS1233 will continue to monitor the
RST
line. If the line is still low, the DS1233 will
continue to monitor the line looking for a rising edge. Upon detecting a release, the DS1233 will force the
RST
line low and hold it low for 350ms.
NOTE:
For proper operation with an external pushbutton, a capacitor between 100pF and 0.01mF must be
connected between
RST
and ground. In applications where additional reset current is required, a
minimum capacitance of 500pF should be used, along with a parallel external pull-up resistor of
1kW minimum.
BLOCK DIAGRAM
Figure 1
APPLICATION EXAMPLE
Figure 2
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DS1233
ABSOLUTE MAXIMUM RATINGS*
Voltage on V
CC
Pin Relative to Ground
Voltage on I/O Relative to Ground
Operating Temperature Range
Storage Temperature Range
Soldering Temperature
*
-0.5V to +7.0V
-0.5V to V
CC
+0.5V
-40°C to +85°C
-55°C to +125°C
260°C for 10 seconds
This is a stress rating only and functional operation of the device at these or any other conditions
above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS
PARAMETER
Supply Voltage
SYMBOL
V
CC
MIN
1.2
TYP
5.0
MAX
5.5
(-40°C to +85°C)
UNITS
V
NOTES
1
DC ELECTRICAL CHARACTERISTICS
PARAMETER
Low Level @
RST
Output Current @ 0.4V
Operating Current
V
CC
Trip Point 5%
V
CC
Trip Point 10%
V
CC
Trip Point 15%
Output Capacitance
Pushbutton Detect
Pushbutton Release
Internal Pull-Up Resistor
SYMBOL
V
OL
I
OL
I
CC
V
CCTP0
V
CCTP1
V
CCTP2
C
OUT
PB
DV
PB
RD
R
P
(-40°C to +85°C; V
DD
= 5V
±
10%)
MIN
+8
50
4.50
4.25
4.0
1.8
0.3
3.75
5
4.625
4.375
4.125
4.75
4.49
4.24
10
3.3
0.8
6.25
TYP
MAX
0.4
UNITS
V
mA
mA
V
V
V
pF
V
V
kW
1
1, 2
1
1
1
NOTES
1
AC ELECTRICAL CHARACTERISTICS
PARAMETER
RESET Active Time
V
CC
Detect to
RST
V
CC
Slew Rate (4.75V - 4.00V)
V
CC
Slew Rate (4.00V - 4.75V)
Pushbutton Debounce
V
CC
Detect to RST
SYMBOL
t
RST
t
RPD
t
F
t
R
PB
DB
t
RPU
(-40°C to +85°C; V
CC
= 5V
±
10%)
MIN
250
300
0
250
250
350
350
450
450
TYP
350
MAX
450
100
UNITS
ms
ns
ms
ns
ms
ms
NOTES
NOTES:
1) All voltages are referenced to ground.
2) With a 100pF to 0.01mF capacitor connected from
RST
to ground.
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