FM3808

The FM3808 combines a 256Kb FRAM array with a real-time clock and a system supervisor function. An external 32.768 kHz crystal drives the timekeeping function. It maintains time and date settings in the absence of system power through the user's choice of backup power source either a capacitor or battery.In either case data in the memory array does not depend on the backup source, it remains nonvolatile in FRAM. In addition to timekeeping, the FM3808 includes a system supervisor to manage low VDD power conditions and a watchdog timer function. A programmable interrupt output pin allows the user to select the supervisor functions and the polarity of the signal.

Both the FRAM array and the timekeeping function are accessed through the memory interface. The upper 16-address locations of the memory space are allocated to the timekeeping registers rather than to memory. The FRAM array provides data retention for 10 years in the absence of system power, and is not dependent on the backup power source for the clock. This eliminates system concerns over data loss in a traditional battery-backed RAM solution. In addition, clock and supervisor control settings are implemented in FRAM rather than battery-backed RAM, making them more dependable. The FM3808 offers guaranteed operation over an industrial temperature range of -40°C to +85°C.