FAIRCHILD FM1233BFS3X

FM1233B
3-Pin µC Supervisor Circuit
General Description
Features
The FM1233B is a supervisor circuit that monitors a microprocessor power supply or other system voltage and issues a reset
pulse when a fault condition exists. Several different threshold
voltages are offered to accommodate 5V systems with different
tolerances.
■ Precision monitoring of 5V and lower voltage microprocessor
systems
■ VTH values of 4.62V, 4.38V and 4.12V
■ Automatic restart of microprocessor after power failure
■ 140ms (min) power-on RESET delay (typ.: 256ms)
The device features a precision temperature-compensated voltage reference and comparator. When VCC falls to the threshold
voltage, a RESET pulse is issued, holding the output in the
active state. When power rises above VTH, the reset remains for
approximately 250 ms to allow the system clock and other circuits to stabilize. The reset output of FM1233B is of open-drain
active low type.
■
■
■
■
■
■
Internal 5kΩ pull-up resistor
Other reset choices available: 32 to 128ms
Operating Temperature -40°C to +105°C
Monitors external pushbutton override
Internal switch debounce circuitry
SOT23-3 package
The FM1233B also can monitor a switch closure on its output,
enabling it to recognize an external reset from a pushbutton
switch or a µP. In the case of a switch, the closure will be
debounced by circuitry internal to the FM1233B.
Typical Operating Circuit
VCC
3
Controller
FM1233B
1
2
RESET
GND
Connection Diagram
GND
1
FM1233B
RESET
3
VCC
2
SOT23-3 Package
©2002 Fairchild Semiconductor Corporation
FM1233B Rev. D
1
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FM1233B 3-Pin µC Supervisor Circuit
February 2003
Votage on any pin relative to GND
VCC
RESET
Input Current
Output Current (RESET)
ESD Rating:
Human body model
>2kV
Machine Model
>200 V
Continuous Power Dissipation (TA = 70°C)
SOT23 (derate 4mW above 70°C)
300mW
20mA
Operating Temperature Range
-40°C to +105°C
Storage Temperature Range
-65°C to +150°C
Lead Temperature (soldering, 10s)
+300°C
These are stress ratings only, and functional operation is not implied for these levels or beyond. Exposure to Absolute Maximum
Rating conditions for extended periods may affect device reliability.
-0.3V to +6.0V
-0.3V to (VCC + 0.3V)
20mA
Electrical Characteristics (VCC = 5V; TA = -40°C to +105°C unless otherwise noted)
(Note 1)
Parameter
Symbol
Conditions
Operating Voltage
VCC
Supply Current
ICC
VCC < 5V
Min
Typ
1.2
3
Max
Units
5.5
V
6
µA
Reset Threshold
VTH
FM1233BF
4.40
4.62
4.86
V
Reset Threshold
VTH
FM1233BD
4.16
4.38
4.55
V
Reset Threshold
VTH
FM1233BE
3.91
4.12
4.32
V
Reset Output Voltage
VOL
FM1233B
0.4
V
Reset Timeout Period
tRST
FM1233B
256
560
ms
Pushbutton Detect
PBVDET
FM1233B
VCC = 5V
2.0
V
Pushbutton Release
PBVREL
FM1233B
Note 2
0.3
1.5
V
Isink = 5mA
VCC = VTH(min)
140
0.8
Note 1: Testing at production is done at 25°C only. Limits over temperature are guaranteed by design.
Note 2: C = 100pF, VCC = 5V. It is recommended to connect 100pF capacitor between the Reset pin and Ground pin if pushbutton reset is implemented.
2
FM1233B Rev. D
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FM1233B 3-Pin µC Supervisor Circuit
Absolute Maximum Ratings
FM1233B 3-Pin µC Supervisor Circuit
Pin Descriptions
Pin Number
Name
1
GND
2
RESET
3
VCC
Function
GROUND
RESET remains LOW while VCC is below VTH, and for
at least 140ms after VCC rises above VTH.
Circuit Timing
VCC
3.3V
VTH
1V
GND
RESET
3.3V
VTH
1V
GND
140ms
(min)
When VCC begins to rise, RESET follows it until 1.0V or so is
reached, whereupon the device regains control, RESET is
pulled to ground, etc. When VCC rises above VTH, RESET
comes out of RESET 140 ms later.
When operating properly with 5V VCC (for example), RESET will
also be about 5V. When VCC starts to fall, RESET will follow it
down as shown. When VCC drops below VTH, RESET drops to
ground (“issues a RESET”) and stays there unless VCC also
falls below its minimum operating voltage, approx. 1V. At this
point, the supervisor loses control, and its output may rise, only
to again follow VCC down to the ground.
If it is required that a lower value than GND + 1.0V is needed
on RESET signal during VCC ≤ 1V, a 100K resistor may be used
on the device output to GND.
3
FM1233B Rev. D
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Connecting an External Reset to the FM1233B
VCC
The FM1233B features a highly accurate voltage reference to
which VCC is compared. Once VCC is below the specified
threshold, it will drive the RESET line and continue to hold it low
until VCC returns above the threshold and the time for the
RESET pulse duration has expired. The FM1233B is immune to
short negative going transients on the VCC line. The placement
of a 0.1µF bypass capacitor as close as possible to the VCC pin
provides additional transient immunity.
3
FM1233
1
Controller
2
RESET
For a VCC value below 1.0V, the FM1233B does not sink very
much current on the RESET pin. This is not a problem in most
systems since common devices are not functional in this range.
If it is desired for the FM1233B reset to be functional below this
range, use a 100KΩ pull-down resistor between RESET and
VSS.
GND
100pF
PUSH
BUTTON
Bi-Directional Reset
The FM1233B permits an external pushbutton to initiate a reset.
Such a connection to pin 2 will be debounced, RESET will go
low and recover in typically 250ms. For proper operation, the
external switch should be paralleled by an external capacitor of
100pF to 0.01µF.
4
FM1233B Rev. D
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FM1233B 3-Pin µC Supervisor Circuit
General Description
Part
Number
Top
Marking
RESET
Threshold (V)
Output Type
Package
Type
Packing
Method
FM1233BFS3X
3BF
4.62
Open-Drain, active LOW
3-Pin, SOT23
3000 units in T&R
FM1233BDS3X
3BD
4.38
Open-Drain, active LOW
3-Pin, SOT23
3000 units in T&R
FM1233BES3X
3BE
4.12
Open-Drain, active LOW
3-Pin, SOT23
3000 units in T&R
Note 3: Devices listed above feature 250ms typical reset pulse width. Consult Fairchild Sales for other reset pulse width options.
5
FM1233B Rev. D
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FM1233B 3-Pin µC Supervisor Circuit
Ordering Information
FM1233B 3-Pin µC Supervisor Circuit
Physical Dimensions inches (millimeters) unless otherwise noted
0.021
0.015
0.055
0.047
0.098
0.083
0.120
0.105
0.0059
0.0035
0.040
0.031
0.079
0.071
0-8˚
0.010
0.005
0.004
0.001
0.76
2.29
PKG
CL
0.76
0.95
LAND PATTERN RECOMMENDATION
SOT-23 Package Dimensions
FS Pkg Code AU
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used in accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a significant
injury to the user.
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FM1233B Rev. D
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