What this 1:4 PCIe clock buffer does on the bench
The 9DB403DFLFT is a PLL-based clock buffer purpose-built for PCI Express (PCIe) reference clock distribution. It takes one HCSL input and fans it out to four differential outputs, each configurable as HCSL or LVDS — the output type is set per the application, not hard-wired at the factory. Maximum output frequency is 400 MHz, which covers all PCIe base clocks (100 MHz, 125 MHz, 133 MHz) with headroom for the 400 MHz Gen5 reference if the system ever needs it. The 1:4 ratio means one input drives four loads — typical for a root complex feeding multiple add-in cards or downstream switch ports.
Supply rail and temperature — what to watch
If your board's 3.3 V rail droops below 3.135 V under load, the PLL loses lock and the outputs go indeterminate. The 28-SSOP package (0.209-inch body width, 5.30 mm) is a fine-pitch SSOP — standard footprint, no via-in-pad required. The supplier device package is also 28-SSOP, so the land pattern is the same regardless of which Renesas assembly site ships it.