Texas Instruments LM5071MT-50/NOPB

Overview

LM5071MT-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, IEEE 802.3af-compliant interface, and current-mode PWM controller for flyback/forward DC-DC converters. It supports auxiliary power enable, programmable classification current (9–44 mA), and 50% maximum duty cycle limiting - used in VoIP phones, IP cameras, and wireless access points requiring dual-input (PoE + AC adapter) operation.

For engineers reviewing the LM5071MT-50/NOPB datasheet, LM5071MT-50/NOPB pinout, LM5071MT-50/NOPB application, or LM5071MT-50/NOPB equivalent, key selection criteria include PoE signature/classification compliance, auxiliary startup threshold (2.5 V), UVLO hysteresis (10 µA), 50% duty cycle limit (no slope compensation), and TSSOP-16 package thermal performance (θ_JA = 125 °C/W).

Technical Context

The LM5071MT-50/NOPB implements a two-stage power sequencing architecture: first, the PD interface performs IEEE 802.3af detection (1.8–10 V), classification (12.5–25 V), and inrush current limiting (100 mA); second, the current-mode PWM controller activates only after RTN falls below 1.45 V, enabling soft-start and VCC regulation (7.8 V). Its -50 suffix denotes fixed 50% max duty cycle without slope compensation - optimized for non-isolated topologies where duty cycle >50% is not required.

It integrates an 80 V internal MOSFET switch with R_DS(ON) = 1 Ω (typ), programmable oscillator (505–665 kHz with RT = 10.5 kΩ), and dedicated CS input with 0.5 V cycle-by-cycle current limit threshold. The AUX pin provides forced UVLO release at ≥9.5 V input, enabling seamless switchover between PoE and 12 V AC adapters - critical for uninterrupted operation in enterprise edge devices.

Key Specifications

Pinout & Package

TSSOP-16 package (4.4 mm × 5.0 mm, 0.65 mm pitch), thermally enhanced with exposed pad (recommended soldered to PCB ground plane for θ_JA ≤ 125 °C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM5071MT-80/NOPB, the -50 variant offers simpler loop compensation and lower EMI in non-isolated applications; versus TPS23753APW, it provides unique auxiliary power arbitration but lacks PoE+ support - making LM5071MT-50/NOPB the optimal choice for cost-sensitive, dual-input 802.3af edge devices.

Availability

LM5071MT-50/NOPB is available at Aetrix Electronics and suitable for VoIP phones, IP cameras, and wireless access points requiring stable component supply, long-term industrial lifecycle support, and RoHS-compliant packaging.

Supply support for LM5071MT-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 delivering analog, embedded processing, and connectivity solutions for industrial, automotive, and communications markets.

The LM5071 product line delivers integrated Power over Ethernet PD controllers with auxiliary power interfaces - designed specifically for edge devices that must operate reliably from both PoE and local AC/DC sources.

FAQ

What is the maximum input voltage rating for LM5071MT-50/NOPB?

The LM5071MT-50/NOPB has an absolute maximum VIN-to-VEE rating of 80 V, with operational range specified from 1.8 V to 60 V. This allows robust handling of PoE transients and compatibility with 12 V auxiliary supplies. The internal 80 V MOSFET and UVLO circuitry ensure safe operation across this full range without external clamping components.

Does LM5071MT-50/NOPB support IEEE 802.3at (PoE+)?

No, LM5071MT-50/NOPB is fully compliant with IEEE 802.3af (up to 15.4 W) but does not support 802.3at (PoE+, up to 30 W). Its internal MOSFET is rated for 400 mA continuous current and 1 Ω R_DS(ON), sufficient for Class 0–4 (0.44–12.95 W) but not Class 5–8. For PoE+ applications, TI recommends TPS23753A or TPS2372-4.

How does the AUX pin function in LM5071MT-50/NOPB?

The AUX pin on LM5071MT-50/NOPB provides a 2.5 V threshold (0.5 V hysteresis) to force UVLO release and activate the SMPS controller when an auxiliary 12 V AC adapter is connected - even if VIN is below the normal 25 V UVLO threshold. This enables seamless, automatic switchover between PoE and wall power without external logic or microcontroller intervention.

What is the purpose of the RT/SYNC pin on LM5071MT-50/NOPB?

The RT/SYNC pin on LM5071MT-50/NOPB serves dual functions: (1) connecting an external resistor (e.g., 10.5 kΩ) sets the oscillator frequency to 505–665 kHz for the -50 variant; (2) it accepts narrow ac-coupled synchronization pulses from an external clock - enabling EMI reduction through frequency dithering or multi-phase interleaving in systems with multiple LM5071MT-50/NOPB controllers.

Can LM5071MT-50/NOPB be used in isolated flyback designs?

Yes, LM5071MT-50/NOPB supports isolated flyback topologies via its COMP pin, which provides an open-drain error amplifier output compatible with optocoupler feedback. However, its 50% maximum duty cycle limit (no slope compensation) restricts use to designs where duty cycle remains ≤50% - typically lower-output-voltage or higher-turns-ratio implementations. For >50% duty cycle, LM5071MT-80/NOPB is recommended.