ADM9690

a FEATURES Precision Voltage Monitor (4.31 V) Watchdog Timeout Monitor Selectable Watchdog Timeout—0.75 ms, 1.5 ms, 12.5 ms, 25 ms Two RESET Outputs APPLICATIONS Microprocessor Systems Computers Printers Controllers Intelligent Instruments Power Supply and Watchdog Timer Monitoring Circuit ADM9690 FUNCTIONAL BLOCK DIAGRAM VCC VMON 4.31V ADM9690 OSC SEL1 OSC SEL2 WATCHDOG TIMEBASE RESET(1) TIMER RESET(2) TIMER RESET(1) RESET(2) WATCHDOG INPUT (WDI) WATCHDOG TRANSITION DETECTOR GND GENERAL DESCRIPTION The ADM9690 contains a voltage monitoring comparator and a watchdog timer monitor. It is designed to monitor the 5 V power supply to a microprocessor and the microprocessor operation via a watchdog function. The voltage monitoring comparator monitors the voltage on VMON. If it drops outside tolerance, as will happen during a power-fail, two reset signals are generated. Both reset signals go active (low) simultaneously. They will remain active while VMON is below the threshold, and for 50 ms (RESET(1)) or 60 ms (RESET(2)) after VMON climbs above the reset threshold. RESET(1) is intended to provide a power-on reset signal for the µP while RESET(2) is used to hold additional circuitry in a reset state until the µP has regained control following a power-up. The voltage monitoring circuitry remains operational with VCC as low as 2 V. The watchdog timer monitoring circuit is designed to monitor the activity on the WDI input. This input is normally connected to an output lin...