8.5 ns ZBT SRAM for high-throughput data paths
The Renesas 71V3557S85PFG is a 4.5 Mbit synchronous SRAM organized as 128K x 36 bits, with a zero-bus-turnaround (ZBT) architecture that eliminates dead cycles when switching between read and write. The 8.5 ns access time lets it keep pace with a 100+ MHz bus in a pipelined system, making it a common choice for network buffers, DSP scratchpads, and cache tag stores where every cycle of throughput matters.
128K x 36 organization — why the extra width
The 36-bit word width is wider than the more common x32 or x18 SRAMs. That extra nibble per word is often used to carry a parity or ECC check bit alongside a 32-bit data bus, saving an external logic layer. In a DSP or FPGA-based design, it also allows packing two 18-bit samples per access, effectively doubling the data rate for a given clock frequency.
Package and footprint
Housed in a 100-pin TQFP (14x14 mm body, 0.5 mm pitch), the 71V3557S85PFG is a surface-mount part intended for reflow assembly. The fine pitch demands careful solder-paste stencil design and a controlled reflow profile to avoid bridging. The package is MSL 3 per JEDEC — if the moisture-barrier bag has been open longer than the floor-life window, a bake-out is required before reflow to prevent popcorning.