64Kbit FRAM with SPI — what it replaces and why
The Infineon FM25640B-GTR is a 64Kbit Ferroelectric RAM (FRAM) from the F-RAM™ series, organized as 8K x 8 bits and accessed through an SPI bus at up to 20 MHz. This makes it a direct drop-in for serial EEPROM sockets where the application needs faster writes, higher endurance, or lower write energy.
20 MHz SPI — bus timing and throughput
At 20 MHz the SPI interface delivers a raw read throughput of 20 Mbps. The FRAM technology means a write cycle completes in the same 50 ns clock period as a read — no write-polling, no page-buffer management. For a data-logging application that writes 64 bytes every 10 ms, the FM25640B-GTR finishes the write in under 26 µs versus the several milliseconds a 64-byte page write takes in a typical serial EEPROM. That timing difference matters when the MCU needs to service other interrupts during the store operation.
FRAM endurance — 10^14 cycles versus EEPROM's 10^6
The FM25640B-GTR uses ferroelectric storage with endurance rated at 10^14 read/write cycles, compared to the 10^6 cycles typical of serial EEPROMs. For a system that writes configuration data every power cycle or logs sensor data continuously, that endurance margin eliminates wear-leveling software and the risk of sector failure over a ten-year service life.
Package and supply — 8-SOIC, 5V rail
The supply range is 4.5V to 5.5V, so it runs directly from a 5V rail without a regulator. The SPI bus pins are 5V-tolerant inputs, which means a 3.3V MCU can drive them through a level translator or a simple resistor divider on the output lines. For a 5V-only design, no translation is needed at all.