Texas Instruments LM5071MTX-50/NOPB

Overview

LM5071MTX-50/NOPB from Texas Instruments is a Power over Ethernet (PoE) Powered Device (PD) controller with integrated 80 V, 1 Ω, 400 mA internal MOSFET, current-mode PWM control, IEEE 802.3af compliance, and auxiliary power interface for AC adapter backup. It enables single-chip PoE + auxiliary power handoff in IP phones, wireless access points, and network cameras.

For engineers reviewing the LM5071MTX-50/NOPB datasheet, LM5071MTX-50/NOPB pinout, LM5071MTX-50/NOPB application, or LM5071MTX-50/NOPB equivalent, key selection criteria include 50% max duty cycle limit (no slope compensation), TSSOP-16 package, -40°C to 125°C junction temperature, 200 kHz nominal oscillator frequency, and dual-input (PoE + AUX) power sequencing capability.

Technical Context

The LM5071MTX-50/NOPB implements a fully integrated IEEE 802.3af PD interface with signature detection (1.8–10 V), classification (12.5–25 V), programmable UVLO (2.00 V threshold), and thermal shutdown (165 °C). Its auxiliary power enable pin activates PWM operation below PoE UVLO threshold, supporting seamless switchover from PoE to 12 V AC adapter input.

This variant features a fixed 50% maximum duty cycle limit and no internal slope compensation-optimized for non-isolated flyback or forward converters where duty cycle remains ≤50%. The current-mode PWM controller includes cycle-by-cycle current limiting (0.5 V CS threshold), soft-start (10 µA current source), and 800 mA peak gate drive on OUT pin.

Key Specifications

Pinout & Package

TSSOP-16 package with exposed thermal pad (PW suffix); RoHS-compliant, lead-free, and moisture-sensitive level 2a per JEDEC J-STD-020.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PoE PD controller applications.

Compared with LM5071MTX-80/NOPB, the LM5071MTX-50/NOPB trades duty cycle flexibility for simpler loop compensation and lower gate drive losses in fixed-frequency, ≤50% duty cycle flyback designs; versus TPS23753APWPR, it offers lower BOM cost and integrated AUX enable but lacks PoE+ support and synchronous rectification.

Availability

LM5071MTX-50/NOPB is available at Aetrix Electronics and suitable for IP telephony endpoints, wireless access points, network surveillance cameras, IoT gateways, and industrial PoE-powered edge devices requiring stable component supply across production lifecycles.

Supply support for LM5071MTX-50/NOPB 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 specializing in analog, embedded processing, and power management ICs, with decades of leadership in power-over-Ethernet solutions and industrial-grade controller design.

The LM5071 product line delivers integrated PoE PD controllers optimized for cost-sensitive, space-constrained networked devices requiring dual-input (PoE + auxiliary) power management and robust IEEE 802.3af compliance.

FAQ

What is the key functional difference between LM5071MTX-50/NOPB and LM5071MTX-80/NOPB?

The LM5071MTX-50/NOPB implements a 50% maximum duty cycle limit with no internal slope compensation, making it ideal for non-isolated flyback or forward converters operating strictly below 50% duty cycle. In contrast, the LM5071MTX-80/NOPB supports up to 80% duty cycle and includes slope compensation for stable current-mode control above 50% duty cycle-required for active-clamp or high-input-voltage topologies. Both share identical pinout and PoE interface functionality, but their PWM sections are not interchangeable without circuit redesign.

Can LM5071MTX-50/NOPB operate with a 12 V AC adapter alone, without PoE?

Yes, the LM5071MTX-50/NOPB supports standalone auxiliary operation via its dedicated AUX pin. When a resistor divider raises the AUX pin voltage above 2.5 V (with 0.5 V hysteresis), it forces UVLO release and enables the PWM controller-even if VIN is below the PoE UVLO threshold (e.g., 12 V from an AC adapter). This allows full DC-DC converter operation without PoE present, making LM5071MTX-50/NOPB suitable for hybrid-powered network devices.

What is the minimum external component count required to implement a functional PoE PD using LM5071MTX-50/NOPB?

A minimal functional PoE PD requires: one signature resistor (24.5 kΩ) between VIN and RSIG; one classification resistor (e.g., 82.5 Ω for Class 2) between RCLASS and VEE; two UVLO divider resistors (e.g., 1 MΩ top, 80.6 kΩ bottom for 25 V turn-on); one AUX divider (e.g., 100 kΩ/47 kΩ for ~3.2 V); one soft-start capacitor (e.g., 100 nF on SS); one RT resistor (30.3 kΩ for 200 kHz); plus basic input/output capacitors and a flyback transformer. No external MOSFET or gate driver is needed-the LM5071MTX-50/NOPB integrates the 80 V, 400 mA switch.

Does LM5071MTX-50/NOPB support IEEE 802.3at (PoE+) or only 802.3af?

The LM5071MTX-50/NOPB is designed and specified exclusively for IEEE 802.3af (Type 1) PoE compliance. Its internal 80 V, 400 mA MOSFET and 25.5 W power handling align with Class 0–4 (max 12.95 W delivered) requirements. It does not support 802.3at (PoE+, Type 2), which requires 50 V minimum input, 30 W delivery, and additional detection/classification timing-functions implemented in TI's TPS2375x family. Using LM5071MTX-50/NOPB on a PoE+ PSE may result in incomplete classification or undervoltage shutdown.

How does the LM5071MTX-50/NOPB handle thermal overload during sustained high-current operation?

The LM5071MTX-50/NOPB incorporates a dedicated thermal shutdown circuit that disables both the PoE interface and PWM controller when junction temperature reaches 165 °C, with 25 °C hysteresis (restart at 140 °C). This protects against latch-up or permanent damage during prolonged overload or poor heatsinking. Unlike current-limit-only protection, thermal shutdown responds to cumulative die heating-not just instantaneous current-and remains active until safe temperature is restored, ensuring robust field reliability in sealed enclosures.