Texas Instruments LMK61E2-312M50SIAR

Overview

LMK61E2-312M50SIAR from Texas Instruments is an ultra-low-jitter LVPECL oscillator generating a precise 312.5 MHz reference clock for high-speed serial interfaces. It delivers 90 fs RMS jitter (typical), ±50 ppm total frequency tolerance, and operates from a single 3.3 V supply across –40°C to +85°C. It serves as a drop-in replacement for crystal-based oscillators in FPGA clocking and 10G/25G Ethernet PHY timing.

For engineers reviewing the LMK61E2-312M50SIAR datasheet, LMK61E2-312M50SIAR pinout, LMK61E2-312M50SIAR application, or LMK61E2-312M50SIAR equivalent, key selection criteria include differential LVPECL output compliance up to 1 GHz, PSRR of –70 dBc against supply noise, and factory-programmed fixed-frequency operation with OE-controlled output enable/disable.

Technical Context

The LMK61E2-312M50SIAR integrates a high-stability PLL-based core optimized for low phase noise and robust power supply rejection. Its internal power conditioning enables stable operation under noisy rail conditions without external LDOs. The device supports only LVPECL output format at 312.5 MHz - not reconfigurable to LVDS or HCSL.

It features a dedicated OE (output enable) input with internal pull-up, allowing high-impedance state control of the differential OUTP/OUTN pair. Power-on reset ensures reliable startup within 10 ms after VDD reaches 3.135 V, and output enable/disable transitions occur within 50 µs.

Key Specifications

Pinout & Package

LMK61E2-312M50SIAR uses a 6-pin QFM (7 mm × 5 mm) package, pin-compatible with industry-standard 7050 XO footprints. The SIA package has exposed thermal pad connected to GND for enhanced thermal dissipation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar ultra-low-jitter oscillator applications.

Compared with LMK61E2-312M50SIA, the SIAR variant provides identical timing performance with optimized packaging for volume production; versus Si5338A-B-GM, it trades configurability for lower jitter (90 fs vs. 120 fs typical), reduced power, and elimination of I²C firmware dependencies.

Availability

LMK61E2-312M50SIAR is available at Aetrix Electronics and suitable for 10G/25G Ethernet PHY timing, FPGA reference clocking, and optical transport network line cards requiring stable component supply and guaranteed long-term availability.

Supply support for LMK61E2-312M50SIAR includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor company specializing in analog, embedded processing, and high-performance timing solutions for industrial, automotive, and communications markets.

The LMK61XX family was designed specifically for applications demanding ultra-low jitter, high PSRR, and factory-calibrated precision - targeting next-generation networking, data center, and test equipment where crystal oscillators fall short.

FAQ

What output format does the LMK61E2-312M50SIAR support?

The LMK61E2-312M50SIAR supports LVPECL output only - it is factory-programmed for 312.5 MHz LVPECL operation and cannot be reconfigured to LVDS or HCSL. Its differential outputs (OUTP/OUTN) require 50-Ω termination to VDD–2 V, consistent with JEDEC JESD8-12 standards. This fixed-format design simplifies layout and eliminates configuration overhead compared to programmable alternatives.

Does the LMK61E2-312M50SIAR require external configuration or programming?

No, the LMK61E2-312M50SIAR is fully factory-programmed and requires no external configuration. It ships with 312.5 MHz LVPECL output enabled by default. There is no I²C, SPI, or pin-strapping interface. All timing parameters - including frequency, jitter, and voltage tolerance - are set during manufacturing and verified per datasheet specifications. This makes LMK61E2-312M50SIAR ideal for plug-and-play clocking in production systems.

What is the function of the OE pin on the LMK61E2-312M50SIAR?

The OE (Output Enable) pin on the LMK61E2-312M50SIAR is an LVCMOS-compatible digital control input with internal pull-up. When pulled low, it disables the LVPECL output pair (OUTP/OUTN), placing them in high-impedance state within 50 µs. When left floating or driven high, outputs are active. This hardware-level gating enables dynamic clock shutdown for power management without software interaction or system reset - a key feature for energy-efficient networking equipment.

Can the LMK61E2-312M50SIAR operate from a 2.5 V supply?

No, the LMK61E2-312M50SIAR is specified exclusively for 3.3 V ±5% operation (3.135 V to 3.465 V). It does not support 2.5 V or other supply voltages. Attempting to operate outside this range may cause functional failure or permanent damage. The device draws ~208 mA in active LVPECL mode, and its internal regulators and output drivers are optimized for 3.3 V rail integrity - underscoring the need for proper decoupling per TI's recommended 10 µF / 1 µF / 0.1 µF network.

How does the LMK61E2-312M50SIAR achieve its ultra-low jitter specification?

The LMK61E2-312M50SIAR achieves 90 fs RMS jitter (typical) through a combination of proprietary PLL architecture, on-die power conditioning, and optimized output driver design. Its internal power regulation provides –70 dBc PSRR, rejecting supply noise that would otherwise modulate the VCO. The LVPECL output stage is tuned for minimal edge uncertainty, and the entire signal path - from crystal-less resonator to differential output - is hardened against substrate coupling and thermal drift. These features are validated across –40°C to +85°C and documented in TI's SNAS676D datasheet for LMK61E2-312M50SIAR.