PCIe clock source with 1:4 fanout — what it does
The Renesas (formerly IDT) 557G-05ALF is a PCI Express (PCIe) clock source IC that takes a single-ended clock or crystal input and delivers four differential HCSL or LVDS outputs at up to 200 MHz. The internal PLL cleans up the incoming reference and generates the low-jitter clock family required by PCIe root complexes, switches, and endpoints. The 1:4 fanout ratio means one input feeds four output lanes — useful for distributing a reference clock across a small PCIe switch or multiple downstream devices without adding a separate fanout buffer.
200 MHz ceiling and differential output — what they mean for the bus
The 200 MHz maximum frequency covers PCIe Gen 1 through Gen 3 reference clock requirements (100 MHz typical, with spread-spectrum modulation where needed). The differential output (HCSL or LVDS) is the standard PCIe clock signaling — the 557G-05ALF accepts a single-ended input and converts it to the differential format the PCIe PHY expects, so you don't need an external single-ended-to-differential converter. The No/Yes differential flag means the input is single-ended (clock or crystal) while all four outputs are differential.
Supply and temperature — commercial range, 3.3 V rail
The supply range is 3.135 V to 3.465 V — a tight 3.3 V ±5% window typical of PCIe clock generators. The operating temperature is 0°C to 70°C, so this part is specified for commercial/indoor equipment (servers, switches, desktop PCs, test gear) rather than industrial or outdoor environments. If the design needs -40°C operation, a different PCIe clock part with industrial temperature rating would be needed.
Package and mounting — 20-TSSOP, surface-mount
Housed in a 20-TSSOP (4.40 mm width) surface-mount package. The supplier device package is 20-TSSOP. This is a standard fine-pitch SSOP footprint — no exposed pad, so thermal dissipation is through the leads only. The shipping medium is tube, not tape-and-reel, which matters for automated pick-and-place line setup (tube-fed feeders or manual loading).
Lifecycle and compliance — active, ROHS3
The 557G-05ALF is listed as Active in production status and ROHS3 compliant.