FM1233B Datasheet, PDF (1/6 Pages) Fairchild Semiconductor – 3-Pin μC Supervisor Circuit

February 2003
FM1233B
3-Pin µC 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 µP. 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 5kΩ pull-up resistor
s Other reset choices available: 32 to 128ms
s Operating Temperature -40°C to +105°C
s Monitors external pushbutton override
s Internal switch debounce circuitry
s SOT23-3 package
Typical Operating Circuit
VCC
GND
Connection Diagram
3
FM1233B
1
2
RESET
Controller
GND 1
FM1233B 3 VCC
RESET 2
SOT23-3 Package
©2002 Fairchild Semiconductor Corporation
1
FM1233B Rev. D
www.fairchildsemi.com