Texas Instruments LMK61E2-I4SIAR

Overview

LMK61E2-I4SIAR from Texas Instruments is an ultra-low jitter (90 fs RMS typical @ >100 MHz), programmable oscillator with integrated fractional-N PLL, 4.6–5.6 GHz VCO, and user-selectable LVPECL/LVDS/HCSL outputs in a 7 mm × 5 mm QFM-8 package. It features internal EEPROM for factory- or field-programmable default settings (e.g., 156.25 MHz LVPECL), I²C interface, ±50 ppm total frequency tolerance, and operates from a single 3.3 V supply across –40°C to +85°C. Used as a high-stability clock source for FPGA/processor reference, network line cards, and test equipment.

For engineers reviewing the LMK61E2-I4SIAR datasheet, LMK61E2-I4SIAR pinout, LMK61E2-I4SIAR application, or LMK61E2-I4SIAR equivalent, key selection criteria include RMS jitter performance at target output frequency, output format compatibility (LVPECL up to 1 GHz / LVDS up to 900 MHz / HCSL up to 400 MHz), PSRR (–70 dBc), frequency margining capability, and EEPROM-based self-start behavior without external configuration.

Technical Context

The LMK61E2-I4SIAR implements a fractional-N PLL architecture with a 4.6–5.6 GHz integrated VCO, 50 MHz crystal reference, and configurable integer/fractional feedback dividers. Its output stage supports three differential formats via register-controlled buffer selection, each with defined voltage swing, common-mode level, and rise/fall time specifications.

Power conditioning includes on-chip LDOs isolating analog PLL supplies from digital I²C and output buffers, enabling –70 dBc PSRR against 50 kHz–1 MHz supply ripple. Frequency margining is implemented at two levels: coarse (via output divider) and fine (via oscillator tuning), both accessible through I²C registers and storable in EEPROM.

Key Specifications

Pinout & Package

LMK61E2-I4SIAR uses a 7 mm × 5 mm, 8-pin QFM (SIA) package with wettable flank leads and an exposed thermal pad. Pin 1 is marked by a dot; top view orientation follows JEDEC standard.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar programmable oscillator applications.

Compared with Si51211-D-GM and AK210-01B-EVAL, LMK61E2-I4SIAR uniquely balances field-programmability, EEPROM-based reliability, and sub-100 fs jitter - making it optimal for systems requiring post-manufacture clock tuning, firmware-agnostic boot, and multi-standard interoperability.

Availability

LMK61E2-I4SIAR is available at Aetrix Electronics and suitable for FPGA reference clocking, 10G/25G Ethernet line cards, and medical imaging systems requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for LMK61E2-I4SIAR 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 headquartered in Dallas, Texas, designing and manufacturing analog ICs, embedded processors, and programmable logic devices for industrial, automotive, and communications markets.

The LMK61E2-I4SIAR belongs to TI's Precision Clocks product line, engineered specifically for high-speed serial interface timing, data converter synchronization, and infrastructure equipment where jitter, stability, and programmability are critical system constraints.

FAQ

What is the default output configuration of LMK61E2-I4SIAR at power-up?

The LMK61E2-I4SIAR powers up with factory-programmed EEPROM settings delivering 156.25 MHz LVPECL output. This occurs without external I²C communication - the device starts generating a valid clock within 10 ms of VDD reaching 3.135 V, as specified in Section 5.12 of the datasheet.

Can LMK61E2-I4SIAR generate non-integer output frequencies like 161.1328125 MHz?

Yes. The LMK61E2-I4SIAR uses a fractional-N PLL with 22-bit numerator/denominator resolution to synthesize arbitrary frequencies within its 10–1000 MHz range. 161.1328125 MHz is explicitly validated in Section 5.18 with measured phase noise and jitter performance.

How does the ADD pin affect I²C communication?

The ADD pin sets the LSB of the 7-bit I²C slave address: tied to GND = 00, floating = 01, tied to VDD = 10. This allows up to three LMK61E2-I4SIAR devices on one I²C bus without address collision, as confirmed in Table 4-1 and Section 7.3.2 of the datasheet.

Is external termination required for LVPECL output operation?

Yes. LVPECL mode requires 150 Ω pull-down resistors from OUTP and OUTN to VCC–2 V (typically 1.3 V), as shown in Figure 6-1. These are not integrated and must be placed externally to meet differential swing (700–1200 mV) and common-mode (VDD–1.55 V) specifications.