Texas Instruments LMH6551MMX

Overview

LMH6551MMX from Texas Instruments is a high-speed, fully differential voltage-feedback amplifier optimized for driving high-performance ADCs and balanced transmission lines. It delivers 370 MHz −3-dB bandwidth (±5 V supply), 2400 V/µs slew rate, and −94/−96 dBc HD2/HD3 at 5 MHz - enabling precise differential signaling in IF/RF and video-over-twisted-pair systems.

For engineers reviewing the LMH6551MMX datasheet, LMH6551MMX pinout, LMH6551MMX application, or LMH6551MMX equivalent, this page provides verified technical context, real-world design meaning of key specs, validated pin functions, confirmed alternative options, and supply-chain support for industrial and communications hardware development.

Technical Context

The LMH6551MMX implements a three-channel architecture: two high-gain differential signal paths (V+ and V−) operating in inverting mode, plus an independent common-mode feedback loop that senses output average voltage and forces it to match the VCM pin reference. This enables true single-ended-to-differential conversion without external baluns.

Its voltage-feedback topology uses external gain-setting resistors (e.g., RF = RG = 365 Ω for G = +1), with internal 50-kΩ resistive divider establishing mid-supply VCM when the pin is left floating. The amplifier requires ±5 V, +5 V, or +3.3 V operation - performance degrades predictably with lower supply voltage (e.g., SSBW drops from 370 MHz to 320 MHz at 3.3 V).

Key Specifications

Pinout & Package

VSSOP-8 package (3.00 mm × 3.00 mm), thermally enhanced for high-speed analog operation with exposed thermal pad (connected to V− internally per TI layout guidelines).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar differential amplifier applications.

Compared with THS4561DR and ADA4940-1ARZ, the LMH6551MMX uniquely balances ultra-high speed (370 MHz), exceptional linearity (−96 dBc HD3), and flexible VCM control - making it the only option among the three capable of driving 105-MSPS+ ADCs with full dynamic range at IF frequencies up to 185 MHz.

Availability

LMH6551MMX is available at Aetrix Electronics and suitable for high-speed data acquisition, video transmission, and wireless infrastructure requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LMH6551MMX 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 leader delivering analog and embedded processing solutions, with deep expertise in high-speed amplifiers and data converter interface ICs.

The LMH6551MMX belongs to TI's LMH™ high-speed analog portfolio, designed specifically for demanding differential signal conditioning in communications, test equipment, and high-fidelity imaging systems.

FAQ

What is the recommended supply configuration for LMH6551MMX in ADC driver applications?

The LMH6551MMX performs optimally with ±5 V split supplies when driving high-performance ADCs. This configuration delivers maximum 370 MHz −3-dB bandwidth, 2400 V/µs slew rate, and lowest distortion (−96 dBc HD3). For single-supply systems, +5 V with VCM = 2.5 V is viable but reduces SSBW to 350 MHz and slew rate to 1800 V/µs - verify against your ADC's input swing and sampling rate requirements. LMH6551MMX must always have local 0.1 µF ceramic decoupling on both V+ and V− pins.

How does the VCM pin function in LMH6551MMX, and what happens if left unconnected?

The VCM pin on the LMH6551MMX sets the output common-mode voltage via an internal error amplifier that compares sensed output average to the VCM voltage. If left unconnected (floating), internal 50-kΩ resistors bias VCM to mid-supply (e.g., 0 V for ±5 V, 2.5 V for +5 V). However, TI strongly recommends bypassing VCM to ground with a 0.1 µF ceramic capacitor to suppress noise coupling - an unfiltered or floating VCM pin causes output common-mode instability and degraded dynamic range. LMH6551MMX requires this capacitor for production use.

Can LMH6551MMX be used for single-ended input to differential output conversion?

Yes - the LMH6551MMX natively supports single-ended-to-differential conversion using only the +IN pin (pin 8) while grounding −IN (pin 1) or terminating it to VCM. Its integrated common-mode feedback loop automatically adjusts +OUT and −OUT to maintain equal amplitude and opposite phase, eliminating need for external baluns or transformer coupling. This is confirmed in TI's datasheet Section 8.1 and Figure 23. LMH6551MMX achieves −70 dB output balance error at 10 MHz in this mode, making it ideal for cost-sensitive SE-to-DE interfaces.

What are the thermal limitations of LMH6551MMX in VSSOP-8 package at full performance?

In VSSOP-8 (DGK) package, the LMH6551MMX has a junction-to-ambient thermal resistance (RθJA) of 235°C/W. At ±5 V supply and 12.5 mA quiescent current, power dissipation is ~125 mW - resulting in ~29°C junction rise above ambient. To maintain full specifications up to +125°C ambient, ensure PCB copper area under the thermal pad is ≥100 mm² with ≥4 thermal vias to inner ground plane. Exceeding TJ = 150°C (absolute max) risks parametric shift and long-term reliability loss. LMH6551MMX thermal derating begins above +105°C case temperature.

Which external resistors are required for gain setting, and how critical is their matching?

The LMH6551MMX requires four external resistors: two gain-setting (RG1, RG2) and two feedback (RF1, RF2), typically configured as RG1 = RG2 and RF1 = RF2 for symmetric operation. For G = +1, TI specifies RF = RG = 365 Ω with 0.1% tolerance. Resistor matching is critical: >0.1% mismatch between RF1/RF2 or RG1/RG2 degrades output balance error and CMRR - e.g., 1% mismatch increases balance error from −70 dB to >−50 dB at 10 MHz. Use matched thin-film arrays (e.g., Vishay ACAS series) for production designs. LMH6551MMX does not operate without these resistors.