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 3.3V and 3.0V systems with different tolerances.

FM1233A 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 asserted for a minimum period (tRST) 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 μP. In the case of a switch, the closure will be debounced by circuitry internal to the FM1233A.

Features

■ Precision monitoring of 3.3V and lower voltage

microprocessor systems

■ VTH values of 3.08V, 2.88V and 2.72V

■ Automatic restart of microprocessor after power failure

■ Reset Timeout Period Choice:

– Options AC and AD: 140ms (min)/256ms (typ)

– Option ABA: 17ms (min)/32ms (typ)

– Available on request: 64ms (typ) and 128ms (typ)

■ Internal 5k? pull-up resistor

■ Operating Temperature -40°C to +105°C

■ Monitors external pushbutton override

■ Internal switch debounce circuitry

■ SOT23-3 package