RF frequency synthesizer with integrated PLL — what it covers and what it needs
The Texas Instruments LMX2491RTWR is a single-chip frequency synthesizer combining a phase-locked loop (PLL) with a VCO core, designed to generate clock or local-oscillator signals up to 6.4 GHz. It accepts a reference clock input and outputs a synthesized clock, with an internal divider and multiplier chain that lets you lock to a multiple or submultiple of the reference. The 2:1 input-to-output ratio means two reference inputs can be selected, but the output path is single-ended — no differential signaling on either side. The part is built for RF and microwave applications: point-to-point radio, radar local oscillators, 5G NR frequency generation, and test equipment that needs a clean, programmable carrier up into C-band. The supply range is 3.15 V to 3.45 V. The industrial temperature grade covers -40°C to 125°C.
Package and mounting — thermal pad is not optional
The LMX2491RTWR comes in a 24-lead WFQFN with an exposed thermal pad (4 mm × 5 mm body,). That pad must be soldered to a PCB copper land with thermal vias to a ground plane; without it, the junction temperature rises well above the 125°C limit under continuous operation at the upper frequency range. The package is surface-mount only, supplied in Tape & Reel or Cut Tape — no tube or tray option.
Lifecycle and sourcing reality
The LMX2491RTWR is listed as Active and ROHS3 compliant. There is no LTB notice or NRND flag in the record — this part is still in regular production and available through the standard TI distribution network. For a BOM line that needs an RF PLL up to 6.4 GHz, this is a current-design-in candidate, not a last-time-buy scavenge.