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FM1233A 3-Pin C Supervisor Circuit
November 2001
FM1233A 3-Pin C Supervisor Circuit
General Description
The FM1233A 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 3V systems with different tolerances. 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 FM1233A is of open-drain active low type. The FM1233A 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 FM1233A.
Features
I Precision monitoring of 3.3V and lower voltage microprocessor systems I VTH values of 2.88V, 2.72V I Automatic restart of microprocessor after power failure I 140ms (min) power-on RESET delay (typ.: 256ms) I Internal 5k pull-up resistor I Other reset choices available: 32 to 128ms I Operating Temperature -40C to +105C I Monitors external pushbutton override I Internal switch debounce circuitry I SOT23-3 package
Typical Operating Circuit
VCC
3
FM1233A Controller
1
GND
2
/RESET
Connection Diagram
GND 1 FM1233A 3 VCC /RESET 2
SOT23-3 Package
(c) 2001 Fairchild Semiconductor Corporation FM1233A Rev. B
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FM1233A 3-Pin C Supervisor Circuit
Absolute Maximum Ratings
Voltage on any pin relative to GND VCC /RESET Input Current Output Current (/RESET) -0.3V to +6.0V -0.3V to (VCC + 0.3V) 20mA 20mA Storage Temperature Range Lead Temperature (soldering, 10s) -65C to +150C +300C Continuous Power Dissipation (TA = 70C) SOT23 (derate 4mW above 70C) Operating Temperature Range 300mW -40C to +105C
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 (VCC = 3.3V; TA = -40C to +105C unless otherwise noted) (Note 1) Parameter
Operating Voltage Supply Current Reset Threshold Reset Threshold Reset Output Voltage Reset Output Voltage Reset Timeout Period Pushbutton Detect Pushbutton Release
Symbol
VCC ICC VTH VTH VOH VOL tRST PBVDET PBVREL
Conditions
VCC < 3.3V FM1233AC FM1233AD FM1233A FM1233A FM1233A FM1233A FM1233A VCC = 3.3V Note 2 ISOURCE = 150 A VCC = VTH(max) ISINK = 5mA VCC = VTH(min)
Min
1.2
Typ
3.3 3
Max
5.5 6 2.97 2.86
Units
V A V V V
2.70 2.58 0.8VCC
2.88 2.72
0.4 140 0.8 0.3 256 560 2.0 1.5
V ms V V
Note 1: Testing at production is done at 25C only. Limits over temperature are guaranteed by design. Note 2: C = 100pF, VCC = 3.3V. It is recommended to connect 100pF capacitor between the Reset pin and Ground pin if pushbutton reset is implemented.
2
FM1233A Rev. B
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FM1233A 3-Pin C Supervisor Circuit
Typical Operating Characteristics
Supply Current Vs. Temperature
10 8
10 8 6 4 2 -55C +25C +110C 0
ICC (A)
6 4 2 0
VCC = 3.3V
Temperature (C)
Power up Reset Timeout Vs. Temperature
Power up Reset timeout (ms)
600 500 400 300 200 100 -40C +25C +105C
600 500 400 300 200 100
Temperature (C)
3
FM1233A Rev. B
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FM1233A 3-Pin C Supervisor Circuit
Pin Descriptions
Pin Number
1 2
Name
GND /RESET GROUND
Function
/RESET remains LOW while VCC is below VTH, and for at least 140ms after VCC rises above VTH.
3
VCC
Circuit Timing (Ex: FM1233A)
VCC 3.3V
VTH
1V
GND RESET 3.3V
VTH
1V
GND
140ms (min)
When operating properly with 3V VCC (for example), /RESET will also be about 3V. 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.
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. 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.
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FM1233A Rev. B
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FM1233A 3-Pin C Supervisor Circuit
General Description
The FM1233A 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 FM1233A is immune to short negative going transients on the VCC line. The placement of a 0.1F bypass capacitor as close as possible to the VCC pin provides additional transient immunity. For a VCC value below 1.0V, the FM1233A 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 FM1233A reset to be functional below this range, use a 100K pull-down resistor between /RESET and VSS.
Connecting an External Reset to the FM1233A
VCC
3
FM1233 Controller
1
GND
100pF
2
/RESET
PUSH BUTTON
Bi-Directional Reset
The FM1233A 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.
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FM1233A Rev. B
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FM1233A 3-Pin C Supervisor Circuit
Ordering Information
Part Number
FM1233ACS3X FM1233ADS3X
Top Marking
3AC 3AD
RESET Threshold (V)
2.88 2.72
Output Type
Open-Drain, active LOW Open-Drain, active LOW
Package Type
3-Pin, SOT23 3-Pin, SOT23
Packing Method
3000 units in T&R 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.
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FM1233A Rev. B
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FM1233A 3-Pin C Supervisor Circuit
Physical Dimensions inches (millimeters) unless otherwise noted
0.45~0.60 0.20 MIN 2.40 0.10
0.40 0.03
1.30 0.10
0.03~0.10 0.38 REF
0.40 0.03 0.96~1.14 2.90 0.10
0.12 -0.023
+0.05
0.95 0.03 0.95 0.03 1.90 0.03 0.508REF
SOT-23 Package Dimensions FS Pkg Code AU
Life Support Policy
Fairchild's products are not authorized for use as critical components in life support devices or systems without the express written approval of the President of Fairchild Semiconductor Corporation. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user.
Fairchild Semiconductor Americas Customer Response Center Tel. 1-888-522-5372 Fairchild Semiconductor Europe Fax: +44 (0) 1793-856858 Deutsch Tel: +49 (0) 8141-6102-0 English Tel: +44 (0) 1793-856856 Francais Tel: +33 (0) 1-6930-3696 Italiano Tel: +39 (0) 2-249111-1
0.97REF
2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.
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Fairchild does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and Fairchild reserves the right at any time without notice to change said circuitry and specifications.
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FM1233A Rev. B
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