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General Description

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.

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.

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

■ 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)

■ Internal 5k? 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