The Cypress CY7B991-5JCT is a PLL-based fanout buffer and zero delay buffer from the RoboClock series. It takes one CMOS input and distributes it to eight CMOS outputs at up to 80 MHz, with the internal PLL aligning the output edges to the input for zero propagation delay.
1:8 fanout and 80 MHz ceiling — sizing the clock tree
The 1:8 input-to-output ratio means a single CY7B991-5JCT can drive up to eight loads from one clock source, reducing the number of buffers on the board. The 80 MHz maximum frequency covers most standard logic and memory interfaces — SDRAM, 10/100 Ethernet MACs, and 8- or 16-bit microcontrollers — but falls short for gigabit-class serial links or DDR3/4 clocking. If your design runs above 80 MHz, you need a different part. Supply voltage is 4.5 V to 5.5 V, so this is a 5 V nominal part.
Package and footprint — 32-PLCC with J-leads
The CY7B991-5JCT comes in a 32-lead PLCC with J-leads (bent under the body). This is a surface-mount package that can also be socketed with a PLCC socket. The J-lead footprint is less common than gull-wing (SOIC, TSSOP) — verify your PCB land pattern matches the J-lead geometry. The supplier device package is 32-PLCC (11.43x13.97 mm).
For a BOM line, this is a low-risk part to qualify — no last-time-buy scramble, no forced redesign.