PCIe reference clock in a 16-pin QFN — what this part does
The Renesas 5V41234NLG is a single-output PCI Express clock generator with an integrated PLL. It takes a single-ended LVCMOS or crystal input and produces a differential HCSL or LVDS output at up to 100 MHz, making it a direct fit for a PCIe reference clock tree where you need exactly one clean differential pair from a local oscillator or board-level clock. The 1:1 input-to-output ratio means this is a buffer or clean-up PLL, not a fanout device — one clock in, one clock out, with the PLL cleaning up jitter and generating the differential swing the PCIe PHY expects. The 3.135 V to 3.465 V supply range keeps it on the standard 3.3 V rail, and the 0°C to 70°C operating temperature limits it to commercial indoor gear — think servers, switches, and test equipment, not a truck or a rooftop radio.
100 MHz ceiling and what it means for your PCIe generation
The 100 MHz maximum frequency is the hard ceiling for the output. PCIe Gen 1 through Gen 3 all use a 100 MHz reference clock (the SerDes multiplies it internally), so this part covers those generations. If you are designing for Gen 4 or Gen 5, which still use 100 MHz but with tighter phase jitter requirements, check whether the 5V41234NLG's jitter performance meets the spec — the datasheet's phase noise plots will tell you. The PLL is present and doing the work, but the jitter cleanup margin is what matters at higher data rates.
Package and mounting — 16-VFQFN with exposed pad
The 16-VFQFN package with exposed pad (3x3 mm body) is a surface-mount part that needs a thermal via pattern under the paddle for both heat sinking and ground return. The exposed pad is the primary thermal path — without it, the junction temperature climbs quickly if the part is running near the 100 MHz limit in a warm enclosure. The 0°C to 70°C commercial temperature grade means this is not rated for extended industrial or automotive environments, so keep it on the indoor PCB.
Sourcing and lifecycle — active, no LTB worry
The 5V41234NLG carries an Active product status and ROHS3 compliance. No second-source or direct replacement is listed in the official records, so dual-sourcing would require qualifying a different PCIe clock generator from the same or another vendor.