FM31278 – FRAM-Enhancedâ„¢ Processor Companion with 2-wire serial interface


This integrated, single-chip solution replaces discrete components to reduce board space and cost in processor-based metering system.

The FM31278 combines 256 kilobits of nonvolatile F-RAM memory with an industry-standard 2-wire bus and a real-time clock/calendar (RTC) that operates with a low-cost 12.5pF crystal. 

The RTC can be battery-backed or capacitor-backed with no additional circuits (i.e. battery crossover, capacitor charging circuit) and draws less than 1 microamp.

The device also boasts a superior trickle charger that can typically charge a 1 Farad supercapacitor in less than three hours, allowing designers to use a capacitor as a backup supply without any additional components. 

Other features of the FM31278 include a programmable low-VDD reset; a programmable watchdog timer; a manual reset function; a nonvolatile event counter; a lockable serial number; and a general-purpose comparator that can be used for early warning power-fail interrupts (NMI). 

The device operates from 2.7 to 5.5 volts over the entire industrial temperature range (-40 degrees C to +85 degrees C) and is available in a green 14-pin SOIC package.

F-RAM offers three distinct benefits in advanced metering designs:

  • NoDelay™ reads/writes:  F-RAM writes data at bus speed, eliminating the need for a complicated data backup system in the event of power loss.
  • Virtually unlimited endurance:  F-RAM collects data for an unlimited period without wearing out.  In an electric meter F-RAM can be written every second for the life of a meter.  No other nonvolatile memory offers this capability.  Less advanced designs that exclude F-RAM can only afford to write the data when power is failing because alternative memory products wear out quickly if they are written too often.
  • Low power consumption:  F-RAM devices are RAMs and do not require charge pumps and are, therefore, orders of magnitude lower in power during write cycles than floating gate devices such as flash and EEPROM.  During battery-powered data collection, F-RAM devices offer the lowest power operation of any memory solution available, making them ideal for a variety of data collection applications including water and gas meters.