Package and mounting
The Infineon CY15B108QN-40SXI is an 8 Mbit ferroelectric RAM (FRAM) organized as 1M x 8 bits, accessed over a standard SPI bus at up to 40 MHz. It sits in the Excelon™-Auto family, which means it carries AEC-Q100 qualification for automotive use. Unlike EEPROM or Flash, FRAM writes at bus speed with no erase cycle and draws no extra time for a page program — the 40 MHz SPI clock is the write speed. The 1.8V to 3.6V supply range lets it run on a single 1.8V or 3.3V rail without a regulator.
Why the AEC-Q100 grade matters for your BOM
The AEC-Q100 qualification (part of the Excelon™-Auto series) is the main reason to pick this part over a standard FRAM like the FM25V20A-DG. It means the part has passed the automotive stress tests: extended temperature cycling, high-temperature operating life, and ESD robustness. If your design targets a vehicle ECU, ADAS module, or any safety-related system that requires AEC-Q100 parts on the AVL, this part fits without a waiver. The 8 Mbit density is the largest in the Excelon™-Auto SPI FRAM lineup, so it is the choice for data logging, calibration storage, or event recorder buffers where you need non-volatile writes at bus speed.
Package and supply — field-fit notes
The supply range from 1.8V to 3.6V means it can sit on a 1.8V MCU rail or a 3.3V system rail without level shifters on the SPI lines, as long as the host's I/O voltage is compatible. At 40 MHz, the SPI bus timing is tight but within the range of most Cortex-M SPI peripherals; check the setup/hold times against your MCU's datasheet if you are running at the full clock rate.