The Infineon CY7C12701KV18-400BZXC is a 36Mbit synchronous DDR II SRAM organized as 1M x 36, clocked at 400 MHz over a parallel interface. It operates from a 1.7V to 1.9V core supply and is housed in a 165-ball FBGA (13x15 mm) for surface-mount assembly. This is a volatile memory part — data is retained only while power is applied — targeted at high-bandwidth, low-latency applications such as network packet buffers, telecom line cards, and test equipment where the DDR II bus eliminates dead cycles on back-to-back reads and writes.
At 400 MHz the DDR II interface transfers data on both clock edges, so the effective data rate is 800 MT/s per pin. For a 36-bit-wide bus that translates to roughly 28.8 Gbit/s of raw bandwidth into the SRAM array. That throughput is what makes this part a fit for designs that need to hold lookup tables or packet buffers with deterministic access latency — think 10G/40G Ethernet forwarding engines or high-speed oscilloscope acquisition memory. The trade-off is the 1.7V to 1.9V supply rail: the board needs a dedicated regulator, not a shared 3.3V or 2.5V plane.
Obsolete — the sourcing reality
Infineon lists the CY7C12701KV18-400BZXC as obsolete. That means new-production factory orders are no longer accepted. If your design can tolerate a re-spin, the broader CY7C12701KV18 family includes other speed and temperature variants that may still be active — but no pin-compatible drop-in replacement is documented.
Package and temperature — board-fit constraints
The 165-FBGA (13x15 mm) footprint is a 1.0 mm ball-pitch array — standard for high-density routing but requires at least four layers on the PCB to escape the inner balls. No industrial or automotive qualification here, so skip this part for outdoor base stations or engine controllers.