64Kbit I²C EEPROM in a 2x3 mm package
It supports a 1 MHz clock frequency and a 450 ns access time, with a write cycle time of 5 ms per word or page. The wide supply range from 1.7V to 5.5V lets it bridge 1.8V and 3.3V or 5V logic domains without a level shifter.
Obsolete — plan the replacement now
STMicroelectronics lists the M24C64-FMB6TG as Obsolete. That means no further production runs; the only channel is surplus or broker inventory. If you're qualifying a new build, look at the current-generation M24C64-W or M24C64-R series parts from ST — they share the same 64Kbit I²C EEPROM core and are available in similar UFDFPN packages. For an existing BOM, verify the exact footprint and supply voltage before swapping; the newer parts maintain the 1.7V to 5.5V range and 1 MHz clock.
The supply range covers 1.8V, 2.5V, 3.3V, and 5V rails without an external regulator. That simplifies BOM consolidation when the same EEPROM is used across boards with different logic families.
Surface-mount footprint and handling
MSL level is not stated in this listing, but typical for this package class is MSL 1 or 3 — if the reel's moisture barrier bag is compromised, a bake before reflow is prudent.