Microchip Technology LE87251NQCT

Overview

LE87251NQCT from Zarlink Semiconductor is a dual-channel, high-voltage differential line driver IC designed for full-rate ADSL2+ and HDSL systems. It integrates four wideband amplifiers (A/B for channel 1, C/D for channel 2), delivers ±11.1 V single-ended output swing into 100 Ω, supports ±5 V to ±12 V dual supplies or +10 V to +24 V single supply, and features fixed 13× voltage gain with 450 mA peak output drive capability.

For engineers reviewing the LE87251NQCT datasheet, LE87251NQCT pinout, LE87251NQCT application, or LE87251NQCT equivalent, this device serves as a low-power, RoHS-compliant QFN-packaged solution for DSL line driving where MTPR > −70 dBc, THD < −75 dBc at 1 MHz, and thermal management via exposed pad are critical selection criteria.

Technical Context

The LE87251NQCT implements two independent differential driver channels using Zarlink's HV30 Bipolar SOI process, enabling stable operation down to low quiescent current (4 mA per amplifier) while maintaining >200 V/µs slew rate and >−75 dBc THD into 60 Ω. Each channel comprises matched amplifier pairs (A/B and C/D) with dedicated enable pins (ENAB/ENCD) and shared common-mode bias inputs (VCMAB/VCMCD).

It operates across −40°C to +85°C ambient, supports transformer-coupled line termination with active/passive schemes, and includes on-chip output clamping to prevent damage from transients - all without requiring external gain-setting resistors due to its internal fixed 13× gain architecture.

Key Specifications

Pinout & Package

LE87251NQCT uses a thermally enhanced 16-pin QFN package (4 mm × 4 mm) with an exposed die pad for PCB heat sinking. The pad must be soldered to a copper plane with thermal vias per Zarlink layout guidelines.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-channel DSL line driver applications.

Compared with LE87251NQCT, LE87252NQCT extends usable bandwidth for next-gen DSL standards but increases power consumption, while MAX22026ETE+ trades high-voltage drive capability for integration and low-voltage operation - making neither a drop-in replacement but rather application-specific alternatives.

Availability

LE87251NQCT is available at Aetrix Electronics and suitable for DSLAM line cards, ADSL2+ customer premises equipment, and HDSL repeater modules requiring stable component supply, long-term lifecycle support, and RoHS-compliant green packaging.

Supply support for LE87251NQCT 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

Zarlink Semiconductor was a fabless semiconductor company specializing in communications ICs, acquired by Microsemi in 2011 and later integrated into Microchip Technology. It pioneered high-performance analog front-ends for broadband access.

The LE87251NQCT belongs to Zarlink's BD870 Series of DSL line drivers, engineered specifically for low-power, high-fidelity differential signaling in carrier-grade ADSL2+/HDSL infrastructure with emphasis on thermal efficiency and transformer interface simplicity.

FAQ

What is the recommended power supply configuration for LE87251NQCT in ADSL2+ applications?

The LE87251NQCT supports both dual-supply (±12 V) and single-supply (+24 V) operation. For ADSL2+ line driving, ±12 V is recommended to maximize symmetric output swing and minimize even-order distortion. Decoupling requires a 2.2 µF tantalum and 0.1 µF ceramic capacitor per supply rail, placed close to the VS+ and VS− pins. Ground connections for bypass capacitors must tie together before returning to system ground to avoid current loops.

Does LE87251NQCT require external gain-setting resistors?

No, the LE87251NQCT features an internal fixed voltage gain of 13.0×, eliminating the need for external feedback or gain-setting resistors. This simplifies PCB layout, improves gain accuracy across temperature (±0.1 V/V variation), and reduces component count. The fixed gain is implemented in the HV30 Bipolar SOI process and is guaranteed across the full operating temperature range.

How does the enable/disable functionality work on LE87251NQCT?

The LE87251NQCT provides independent channel control via ENAB (channel 1) and ENCD (channel 2). Driving either pin to ground enables its respective amplifier pair; leaving it floating or pulling it high (≤6 V) disables the channel. Internal 50 kΩ pull-up resistors bias ENAB/ENCD to 2.5 V when unconnected. In disabled state, quiescent current drops to ≤0.4 mA per amplifier, supporting dynamic power management.

What thermal design considerations apply to LE87251NQCT?

The LE87251NQCT uses a 4 mm × 4 mm QFN package with an exposed thermal pad that must be soldered to a minimum 4 mm × 4 mm copper area on the PCB, connected via ≥4 thermal vias (0.3 mm diameter) to inner ground planes. Failure to implement this results in junction temperature exceeding +150°C under full load. Thermal resistance (θ_JA) is specified at 35°C/W only with this layout - otherwise, derating is required.

Can LE87251NQCT drive a 60 Ω load directly without external components?

Yes, the LE87251NQCT is characterized to deliver 40.5 V_p-p differential output into a 60 Ω load with −75 dBc THD at 1 MHz. However, series termination resistors (e.g., 49.9 Ω) are still required per the typical application circuit to prevent oscillation, limit fault current during line shorts, and ensure stability with capacitive loading. Direct connection without these resistors risks instability or excessive DC current flow.