Texas Instruments LMK61A2-644M53SIAR

Overview

LMK61A2-644M53SIAR from Texas Instruments is an ultra-low jitter LVDS oscillator generating a precise 644.53125 MHz reference clock for high-speed serial interfaces. It delivers ±50 ppm total frequency stability, 90 fs RMS jitter (typical at >100 MHz), and operates from a single 3.3 V supply in industrial temperature range (–40°C to +85°C). Its primary role is timing reference generation in FPGA transceiver lanes and optical transport systems.

For engineers reviewing the LMK61A2-644M53SIAR datasheet, LMK61A2-644M53SIAR pinout, LMK61A2-644M53SIAR application, or LMK61A2-644M53SIAR equivalent, key selection criteria include differential output format compatibility (LVDS), 644.53125 MHz exact frequency requirement, sub-100 fs jitter performance, PSRR of –70 dBc, and 7 mm × 5 mm QFM package constraints.

Technical Context

The LMK61A2-644M53SIAR implements an integrated PLL-based architecture with factory-programmed frequency synthesis, eliminating external crystal or loop filter components. Its internal power conditioning provides robust supply noise immunity, enabling direct integration into noisy digital power domains without additional filtering.

It supports only LVDS output format at this specific frequency variant, with differential pair (OUTP/OUTN) termination optimized for 100 Ω differential loads. The OE pin enables LVCMOS-compatible output disable control with internal pull-up, allowing dynamic power gating in system-level timing management.

Key Specifications

Pinout & Package

LMK61A2-644M53SIAR uses a 6-pin QFM (Quad Flat No-lead) package measuring 7.0 mm × 5.0 mm, pin-compatible with standard 7050 XO footprints. Thermal pad is connected to GND for optimal heat dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LMK61E2-644M53SIAR, the LMK61A2-644M53SIAR trades ±25 ppm stability for broader industrial qualification and lower cost; versus Si5338A-D-GM, it eliminates I²C dependency and reduces layout complexity while maintaining sufficient jitter performance for 100G applications.

Availability

LMK61A2-644M53SIAR is available at Aetrix Electronics and suitable for OTN transport systems, 100G Ethernet switches, and FPGA-based test equipment requiring stable component supply, consistent parametric performance, and long-term lifecycle support.

Supply support for LMK61A2-644M53SIAR 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, with decades of leadership in precision clock generation.

The LMK61XX product line was designed specifically for high-speed communication infrastructure, delivering factory-programmed, ultra-low jitter oscillators that replace quartz-based solutions in 10G–400G networking, optical transport, and wireless baseband applications.

FAQ

What output format does the LMK61A2-644M53SIAR support?

The LMK61A2-644M53SIAR supports LVDS output only at its factory-programmed frequency of 644.53125 MHz. Unlike other variants in the LMK61XX family, this part is not configurable for LVPECL or HCSL. Its LVDS output delivers 300–480 mV differential swing into 100 Ω loads, with guaranteed rise/fall times of 150–250 ps.

Does the LMK61A2-644M53SIAR require external programming or configuration?

No, the LMK61A2-644M53SIAR is factory-programmed and fully operational upon power-up with no external configuration required. It contains no EEPROM or I²C interface. All timing parameters-including frequency, output format, and startup behavior-are hard-coded during manufacturing, ensuring zero firmware dependencies and deterministic boot timing for the LMK61A2-644M53SIAR.

What is the recommended power supply bypassing for the LMK61A2-644M53SIAR?

Texas Instruments specifies a three-capacitor bypass network for the LMK61A2-644M53SIAR: 10 µF (bulk), 1 µF (mid-frequency), and 0.1 µF (high-frequency) ceramic capacitors placed as close as possible to the VDD pin. All capacitors must be mounted on the component side using 0201 or 0402 packages, with short traces and low-inductance connections to the ground plane via multiple vias.

How does the OE pin function on the LMK61A2-644M53SIAR?

The OE (Output Enable) pin on the LMK61A2-644M53SIAR is an LVCMOS input with internal pull-up. When pulled low (≤0.6 V), it disables both OUTP and OUTN outputs, placing them in high-impedance state within 50 µs. When left unconnected or pulled high (≥1.4 V), outputs are active. This enables system-level clock gating without affecting internal oscillator operation.

Is the LMK61A2-644M53SIAR pin-compatible with other LMK61XX devices?

Yes, the LMK61A2-644M53SIAR shares identical 6-pin QFM (7.0 mm × 5.0 mm) packaging and pinout with all members of the LMK61XX family, including LMK61E2-100M, LMK61A2-125M, and LMK61I2-100M. Pin functions (OE, GND, OUTN, OUTP, VDD, NC) are consistent across variants, enabling PCB design reuse and simplified inventory management for the LMK61A2-644M53SIAR and related parts.