36Mbit QDR II SRAM at 400 MHz — what it does
It clocks at 400 MHz on the read and write ports, giving back-to-back bus transactions without dead cycles — the key advantage of QDR II over standard synchronous SRAM. The parallel interface and 1.7V to 1.9V core supply target high-throughput data buffers in network switches, test instrumentation, and baseband processing where every clock cycle carries a valid word.
At 400 MHz the QDR II interface delivers a peak bandwidth of 1.6 Gbps per I/O pin (double-data-rate on both read and write ports). That throughput is what makes this part a fit for designs that cannot stall the pipeline — think packet buffers in 10 GbE line cards or real-time radar processing. The trade-off is tighter timing closure on the PCB: the 400 MHz clock demands controlled-impedance traces and matched-length routing between the SRAM and the controller. The 165-ball FBGA (15x17 mm) footprint gives enough signal layers to route the full 36-bit data bus plus address and control without excessive via stubs.
The CY7C1265V18-400BZXC carries an official Obsolete lifecycle status. Cypress (now part of Infineon) no longer manufactures this density-speed-grade combination. If you are designing a new board, look at current-generation QDR II+ or QDR IV SRAMs from Cypress/Infineon or Renesas that maintain the 1.7V–1.9V supply and 165-ball FBGA footprint, but verify pin compatibility — the QDR II family has multiple ballout revisions.