2002 Fairchild Semiconductor Corporation
1
www.fairchildsemi.com
February 2003
FM1233B 3-Pin C Super
visor Cir
cuit
FM1233B Rev. D
FM1233B
3-Pin C Supervisor Circuit
General Description
The FM1233B is a supervisor circuit that monitors a micropro-
cessor 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.
The device features a precision temperature-compensated volt-
age reference and comparator. When V
CC
falls to the threshold
voltage, a RESET pulse is issued, holding the output in the
active state. When power rises above V
TH
, the reset remains for
approximately 250 ms to allow the system clock and other cir-
cuits to stabilize. The reset output of FM1233B is of open-drain
active low type.
The FM1233B also can monitor a switch closure on its output,
enabling it to recognize an external reset from a pushbutton
switch or a P. In the case of a switch, the closure will be
debounced by circuitry internal to the FM1233B.
Features
s
Precision monitoring of 5V and lower voltage microprocessor
systems
s
V
TH
values of 4.62V, 4.38V and 4.12V
s
Automatic restart of microprocessor after power failure
s
140ms (min) power-on RESET delay (typ.: 256ms)
s
Internal 5k
pull-up resistor
s
Other reset choices available: 32 to 128ms
s
Operating Temperature -40C to +105C
s
Monitors external pushbutton override
s
Internal switch debounce circuitry
s
SOT23-3 package
Typical Operating Circuit
Connection Diagram
SOT23-3 Package
1
FM1233B
Controller
2
3
VCC
GND
RESET
GND
VCC
RESET
1
FM1233B
2
3
FM1233B 3-Pin C Super
visor Cir
cuit
2
www.fairchildsemi.com
FM1233B Rev. D
Absolute Maximum Ratings
Votage on any pin relative to GND
V
CC
-0.3V to +6.0V
RESET
-0.3V to (V
CC
+ 0.3V)
Input Current
20mA
Output Current (RESET)
20mA
ESD Rating:
Human body model
>2kV
Machine Model
>200 V
Continuous Power Dissipation (T
A
= 70C)
SOT23 (derate 4mW above 70C)
300mW
Operating Temperature Range
-40C to +105C
Storage Temperature Range
-65C to +150C
Lead Temperature (soldering, 10s)
+300C
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.
Electrical Characteristics (V
CC
= 5V; T
A
= -40C to +105C unless otherwise noted)
(Note 1)
Note 1
: Testing at production is done at 25C only. Limits over temperature are guaranteed by design.
Note 2
: C = 100pF, V
CC
= 5V. It is recommended to connect 100pF capacitor between the Reset pin and Ground pin if pushbutton reset is implemented.
Parameter
Symbol
Conditions
Min
Typ
Max
Units
Operating Voltage
V
CC
1.2
5.5
V
Supply Current
I
CC
V
CC
< 5V
3
6
A
Reset Threshold
V
TH
FM1233BF
4.40
4.62
4.86
V
Reset Threshold
V
TH
FM1233BD
4.16
4.38
4.55
V
Reset Threshold
V
TH
FM1233BE
3.91
4.12
4.32
V
Reset Output Voltage
V
OL
FM1233B
I
sink
= 5mA
V
CC
= V
TH
(min)
0.4
V
Reset Timeout Period
t
RST
FM1233B
140
256
560
ms
Pushbutton Detect
PBV
DET
FM1233B
V
CC
= 5V
0.8
2.0
V
Pushbutton Release
PBV
REL
FM1233B
Note 2
0.3
1.5
V
FM1233B 3-Pin C Super
visor Cir
cuit
3
www.fairchildsemi.com
FM1233B Rev. D
Pin Descriptions
Circuit Timing
When operating properly with 5V V
CC
(for example), RESET will
also be about 5V. When V
CC
starts to fall, RESET will follow it
down as shown. When V
CC
drops below V
TH
, RESET drops to
ground ("issues a RESET") and stays there unless V
CC
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 V
CC
down to the ground.
When V
CC
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 V
CC
rises above V
TH
, RESET
comes out of RESET 140 ms later.
If it is required that a lower value than GND + 1.0V is needed
on RESET signal during V
CC
1V, a 100K resistor may be used
on the device output to GND.
Pin Number
Name
Function
1
GND
GROUND
2
RESET
RESET remains LOW while V
CC
is below V
TH
, and for
at least 140ms after V
CC
rises above V
TH
.
3
V
CC
3.3V
V
TH
1V
GND
3.3V
V
TH
1V
GND
V
CC
RESET
140ms
(min)
FM1233B 3-Pin C Super
visor Cir
cuit
4
www.fairchildsemi.com
FM1233B Rev. D
General Description
The FM1233B features a highly accurate voltage reference to
which V
CC
is compared. Once V
CC
is below the specified
threshold, it will drive the RESET line and continue to hold it low
until V
CC
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 V
CC
line. The placement
of a 0.1F bypass capacitor as close as possible to the V
CC
pin
provides additional transient immunity.
For a V
CC
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 100K
pull-down resistor between RESET and
V
SS
.
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 0.01F.
Connecting an External Reset to the FM1233B
1
FM1233
Controller
2
3
V
CC
GND
100pF
PUSH
BUTTON
RESET
FM1233B 3-Pin C Super
visor Cir
cuit
5
www.fairchildsemi.com
FM1233B Rev. D
Ordering Information
Note 3
: Devices listed above feature 250ms typical reset pulse width. Consult Fairchild Sales for other reset pulse width options.
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
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