Most micro-controllers comes with both SRAM volatile memory, and flash or EEPROM for non-volatile (persistent) memory, but Texas Instruments – and other companies – have been selling MCUs with FRAM (Ferroelectric Random Access Memory) and standalone FRAM chip, a non-volatile memory that delivers performance and power efficiency similar to SRAM, and much better endurance that either flash or EEPROM. You don’t see FRAM in that many MCUs and solutions, because it’s more expensive than having SRAM + flash, but some applications requiring ultra low power consumption and non-volatile storage write capabilities may benefit from the technology. Those include data logging, sensor networks, and batteryless applications. Microchip has also it own technology with EERAM, a non-volatile SRAM memory that includes a “shadow” EEPROM used to automatically backup data on power down with a small external capacitor providing enough power to save SRAM to the EEPROM.
Once power is recovered (Vdd > Vtrip), the content of the EEPROM is copied back into the SRAM. The company can hence combines the performance of SRAM with EEPROM non-volatile storage and reliability with this solution. Store and Recall actions can also be triggered by software commands. The end results is similar to what is achieved with FRAM, but Microchip claims EERAM is much cheaper. The company provide both 4Kbit and 16Kbit of the EERAM with the following specifications:
- Capacity – 4Kb – 16Kb
- Interface – I2C
- Non-volatile (with external capacitor)
- Unlimited erase/write cycles
- Instantaneous, random read/write
- Temperature Range – -40°C to +125°C
- 8-pin packages
Just like FRAM, it’s also well suited to data logging applications, however capacity is quite lower since you can get 1 Mbit FRAM chips, and standby current is higher than some other Serial NVSRAM (Non-volatile SRAM) chips. Price starts at $0.50 per unit for 5K orders. Visit Microchip EERAM product page for more details.