High-voltage tolerant watchdog comparator in a low-voltage CMOS technology

A watchdog comparator is presented that is tolerant of supply voltages significantly higher than the process limit for individual CMOS transistors. The circuit demonstrates very low current consumption, and has a fast dynamic response. The described circuit was implemented in the battery charger block of a power management IC for cellular phones. The implemented watchdog comparator is tolerant of input voltages up to 12 V and passes operational life and reliability tests. Extensive evaluation under various start-up conditions shows circuit compliance to contradictory specification parameters. Simulation and measurement data for various power-up transient conditions are presented.