Texas Instruments LM5070MTC-50/NOPB

Overview

LM5070MTC-50/NOPB from Texas Instruments is an IEEE 802.3af-compliant Powered Device (PD) interface and current-mode PWM controller with integrated 80 V, 400 mA MOSFET, 50% maximum duty cycle limit, programmable inrush current limit (75–390 mA), and internal 7.8 V VCC regulator. It enables PoE-powered endpoints such as VoIP phones and wireless access points.

For engineers reviewing the LM5070MTC-50/NOPB datasheet, LM5070MTC-50/NOPB pinout, LM5070MTC-50/NOPB application, or LM5070MTC-50/NOPB equivalent, key selection considerations include IEEE 802.3af signature/classification compliance, inrush current programmability via RCLP, UVLO hysteresis control, TSSOP-16 package thermal performance (θ_JA = 125°C/W), and absence of slope compensation due to its –50 suffix designation.

Technical Context

The LM5070MTC-50/NOPB implements a two-stage power sequencing architecture: first, the PD interface performs detection (1.8–10 V), classification (12.5–20.5 V), and controlled inrush charging via its internal MOSFET; second, the current-mode PWM controller initiates operation only after RTN falls below 1.5 V relative to VEE, ensuring safe SMPS startup.

Its –50 suffix denotes a fixed 50% maximum duty cycle limit without slope compensation, distinguishing it from the –80 variant; oscillator frequency is internally divided by two to enforce precise 50% duty control, and the CS comparator triggers cycle-by-cycle current limiting at 0.5 V threshold with 50 ns leading-edge blanking.

Key Specifications

Pinout & Package

TSSOP-16 package (Package Number PW) with exposed pad thermally bonded to VEE; θ_JA = 125°C/W, suitable for compact PoE endpoint layouts requiring moderate power dissipation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Powered Device interface and PWM controller applications.

Compared with LM5070MTC-80/NOPB, the LM5070MTC-50/NOPB trades duty-cycle flexibility for simpler loop compensation and lower EMI risk in fixed 50% topologies; versus TPS23753APWR, it offers lower cost and zero-firmware operation but lacks PoE+ support and digital control.

Availability

LM5070MTC-50/NOPB is available at Aetrix Electronics and suitable for VoIP phones, wireless access points, network cameras, and thin clients requiring stable component supply and long-term industrial lifecycle support.

Supply support for LM5070MTC-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 connectivity technologies with broad industrial and communications portfolio coverage.

The LM5070 product line delivers integrated PoE PD interface and PWM controllers targeting cost-sensitive, space-constrained Ethernet-powered endpoints where IEEE 802.3af compliance and autonomous power sequencing are essential.

FAQ

What is the primary function of the LM5070MTC-50/NOPB in a PoE system?

The LM5070MTC-50/NOPB serves as a fully integrated IEEE 802.3af Powered Device (PD) interface and current-mode PWM controller. It manages detection, classification, inrush current limiting, and undervoltage lockout for the PD front-end, then regulates isolated or non-isolated DC-DC conversion via its 50% duty-cycle-limited gate driver. Its internal 80 V, 400 mA MOSFET eliminates external high-voltage switching components, and the LM5070MTC-50/NOPB's fixed 50% duty cycle simplifies flyback design without slope compensation.

How does the LM5070MTC-50/NOPB implement IEEE 802.3af signature detection?

The LM5070MTC-50/NOPB implements signature detection by enabling a 25 kΩ resistor between VIN and RSIG pins when input voltage exceeds 1.8 V-matching the IEEE 802.3af required impedance range of 23.75–26.25 kΩ. The device draws less than 10 µA during detection, meets the 0.05–0.12 µF input capacitance requirement, and disables the signature resistor above 11 V to reduce standby power. This hardware-based detection requires no external components beyond the resistor and is validated per SNVS308G specification for the LM5070MTC-50/NOPB.

What distinguishes the LM5070MTC-50/NOPB from the LM5070MTC-80/NOPB variant?

The LM5070MTC-50/NOPB features a fixed 50% maximum duty cycle limit and no slope compensation circuitry, whereas the LM5070MTC-80/NOPB provides an 80% maximum duty cycle with integrated slope compensation. Both share identical pinout, MOSFET specs, and PD interface functions, but the –50 variant uses an internal oscillator divide-by-two to enforce strict 50% duty control-ideal for flyback converters operating near boundary conduction mode. The LM5070MTC-50/NOPB thus simplifies compensation and reduces EMI in fixed-ratio topologies where duty cycle headroom is not required.

Can the LM5070MTC-50/NOPB support non-isolated DC-DC topologies?

Yes, the LM5070MTC-50/NOPB supports non-isolated topologies via its internal error amplifier and 1.25 V reference. The FB pin serves as the inverting input, and the COMP pin provides an open-drain output with internal 5 kΩ pull-up-enabling direct connection to buck or buck-boost feedback networks. For non-isolated designs, the internal error amplifier replaces secondary-side regulation, and the LM5070MTC-50/NOPB's VCC regulator supplies bias from the high-side input, eliminating need for auxiliary windings. This capability is explicitly documented in the SNVS308G datasheet for the LM5070MTC-50/NOPB.

What thermal considerations apply to the LM5070MTC-50/NOPB in TSSOP-16 package?

The LM5070MTC-50/NOPB in TSSOP-16 (PW package) has a junction-to-ambient thermal resistance (θ_JA) of 125°C/W, requiring careful PCB layout for thermal management. The exposed pad must be soldered to a VEE-connected copper pour to maximize heat dissipation. Thermal shutdown activates at 165°C with 25°C hysteresis, and the device operates from –40°C to +125°C junction temperature. Derating is required above 70°C ambient; for example, at 85°C ambient, maximum continuous power dissipation drops to ~0.65 W. These thermal characteristics are measured and specified for the LM5070MTC-50/NOPB per its official TI characterization data.