64 Kbit SPI EEPROM for parameter storage and calibration tables
The Microchip 25AA640-I/SN is a 64Kbit serial EEPROM with an SPI interface, organized as 8K x 8 bits. The 1 MHz maximum clock rate is adequate for boot-time parameter reads and infrequent logging; if your application streams data at higher rates, the 2 MHz 25LC640 sibling is worth a look. The 5 ms write cycle time per word or page means you budget around 2.5 seconds to rewrite the full 64 Kbit array — fine for infrequent updates, not for high-frequency data logging.
ROHS3 compliance covers the EU RoHS exemption structure through 2024 and beyond. For dual-sourcing flexibility, the 25AA640A-I/P is a through-hole DIP variant with the same 64Kbit density and SPI interface, though it ships in a different package and may have slight parametric differences — verify the AC timing before dropping it in as a second source.
SPI bus integration — what the 1 MHz clock means for throughput
At 1 MHz SPI clock, a 64-bit read takes about 72 µs including command and address overhead; a full 8K x 8 page read (64 bytes) runs roughly 640 µs. That is fast enough for boot-time configuration pulls and periodic parameter saves, but if your MCU polls the EEPROM at control-loop rates, the bus occupancy will eat into your margin. The write cycle locks out the bus for 5 ms per page — plan your firmware state machine to retry or queue writes.
Package and footprint — 8-SOIC narrow body
The Tube shipping medium is typical for low-volume production and prototyping; if your pick-and-place line prefers tape-and-reel, the 25AA640T-I/SN variant is the reeled version of the same die.