Texas Instruments LMH6551MA

Overview

LMH6551MA 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, 18 ns settling time to 0.05%, and −94/−96 dBc HD2/HD3 at 5 MHz - enabling precision differential signaling in video-over-twisted-pair and IF/RF receiver front-ends.

For engineers reviewing the LMH6551MA datasheet, LMH6551MA pinout, LMH6551MA application, or LMH6551MA equivalent, this page provides verified technical context, validated pin functions, confirmed package mapping (SOIC-8), real-world application cards, and two rigorously cross-checked alternative parts with documented functional and application-level differences.

Technical Context

The LMH6551MA integrates three functional channels: two high-gain differential signal paths (IN+→+OUT, IN−→−OUT) operating in inverting mode, plus an independent common-mode feedback loop centered on the VCM pin. This architecture 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), while the VCM pin controls output common-mode voltage via a dedicated error amplifier that compares sensed output average against an applied reference - floating VCM defaults to midsupply via internal 50-kΩ resistors.

Key Specifications

Pinout & Package

LMH6551MA is packaged in an 8-pin SOIC (4.90 mm × 3.91 mm body), pin-compatible with industry-standard SOIC-8 footprints and reflow profiles.

Key Features

Applications

Equivalent & Alternatives

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

Compared with THS4561IDR and ADA4940-1ARZ, the LMH6551MA uniquely balances 370-MHz bandwidth, programmable VCM, single/dual supply flexibility, and proven −96 dBc HD3 at 5 MHz - making it optimal for mid-bandwidth, mixed-supply, and VCM-tunable differential signal chains.

Availability

LMH6551MA is available at Aetrix Electronics and suitable for high-speed ADC interface design, video-over-cable transmission, IF amplification, SAW filter buffering, and differential line driving requiring stable component supply across industrial temperature ranges (−40°C to +125°C).

Supply support for LMH6551MA 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 signal conditioning and data converter interfaces.

The LMH6551MA belongs to TI's LMH™ family of high-speed differential amplifiers, designed specifically for precision, wideband differential signal conditioning in communications, test equipment, and high-fidelity data acquisition systems.

FAQ

What is the maximum small-signal bandwidth of the LMH6551MA under ±5-V supply conditions?

The LMH6551MA achieves a 370-MHz −3-dB small-signal bandwidth when operated with ±5-V supplies, VOUT = 0.5 VPP, and G = +1 configuration. This bandwidth is measured differentially and supports applications such as IF amplification up to ~185 MHz fundamental frequency. The LMH6551MA maintains usable gain beyond this point but with increasing attenuation.

Can the LMH6551MA operate from a single 3.3-V supply, and what are the key trade-offs?

Yes, the LMH6551MA supports single 3.3-V operation with VCM = 1.65 V. Key trade-offs include reduced small-signal bandwidth (320 MHz), lower slew rate (700 V/µs), and diminished output swing (±0.9 V peak-to-peak). However, harmonic distortion remains strong at −93 dBc HD2 / −85 dBc HD3 at 5 MHz, making it viable for low-voltage, moderate-bandwidth applications.

How does the VCM pin function in the LMH6551MA, and what happens if it is left unconnected?

The VCM pin sets the output common-mode voltage via an internal error amplifier. When left unconnected, the LMH6551MA defaults to midsupply (e.g., 0 V with ±5 V supplies, 2.5 V with +5 V supply) using internal 50-kΩ resistors. For precise control, drive VCM with a low-impedance reference and bypass with 0.1 µF to ground - coupling noise into VCM directly modulates output common-mode.

What is the recommended layout practice for minimizing balance error in the LMH6551MA?

To minimize balance error (< −70 dB), maintain strict symmetry: use identical trace lengths and widths for IN+, IN−, +OUT, and −OUT; place RF/RG resistors close to the LMH6551MA pins; terminate each output differentially (e.g., 50 Ω to ground per side); and avoid routing VCM near noisy digital traces. Asymmetric parasitics directly degrade differential output fidelity.

Does the LMH6551MA include power-down functionality, and how is it controlled?

No, the LMH6551MA does not feature a dedicated power-down (PD) pin. Unlike later-generation FDAs (e.g., THS4561), the LMH6551MA lacks enable/disable control. Power state is managed solely via supply rails - removing V+ and V− disables operation. For active power gating, external supply switches or load-switch ICs must be used in conjunction with the LMH6551MA.