729 MHz fractional-N PLL — the line-rate ceiling
The SY87739LHY is a fractional-N PLL synthesizer from Microchip's AnyClock® family, clocking up to 729 MHz on the output. That maximum frequency sets the upper bound for the serial line rate it can generate or clean — 729 MHz is enough for 1 GbE, OC-12/STM-4 SONET, and 1x/2x Fibre Channel without an external multiplier.
PECL signaling — what it means for the backplane
Both input and output are PECL (PECL differential), with a 1:1 input-to-output ratio. PECL is the dominant clock standard in telecom and datacom line cards because its differential swing rejects common-mode noise across a backplane. The 3.15 V to 3.45 V supply rail is the PECL VCC range — the output swing is referenced to this rail, so the receiving PECL buffer must share the same supply or use AC-coupling with a bias network.
Industrial temp and exposed-pad thermal path
The 32-TQFP exposed pad (7x7 mm body) pulls heat from the die into a ground-plane via the center pad; the datasheet's RθJA assumes a thermal via array under the pad. Without those vias the junction temperature climbs above the 85°C ambient ceiling at the full 729 MHz toggle rate.
ROHS3 means the part is free of the four phthalates (DEHP, BBP, DBP, DIBP) in addition to the original six RoHS substances, so no exemption-expiry risk for European or California-market builds.