Texas Instruments LM2577T-ADJ/LF02

Overview

LM2577T-ADJ/LF02 from Texas Instruments is a monolithic step-up (boost) switching voltage regulator featuring an integrated 3.0A NPN power switch, 52 kHz fixed-frequency oscillator, and adjustable output voltage via external resistor divider. It operates from 3.5V to 40V input, delivers up to 60V output, and includes current limiting, thermal shutdown, and undervoltage lockout. It is used in battery-powered instrumentation requiring regulated +12V or +15V rails from single Li-ion or multi-cell alkaline supplies.

For engineers reviewing the LM2577T-ADJ/LF02 datasheet, LM2577T-ADJ/LF02 pinout, LM2577T-ADJ/LF02 application, or LM2577T-ADJ/LF02 equivalent, key selection criteria include its TO-220 (T) package thermal performance (θ_JA = 65°C/W), adjustable reference voltage (1.230 V ±1.3%), soft-start function for in-rush current control, and compatibility with standard off-the-shelf boost inductors such as AIE L470 or Pulse PE-53114.

Technical Context

The LM2577T-ADJ/LF02 implements current-mode control architecture, where the error amplifier compares feedback voltage against a precision 1.230 V internal reference and modulates peak switch current to regulate output. Its 52 kHz oscillator sets fixed switching frequency, enabling predictable EMI filtering and stable loop compensation using a single external RC network on the COMP pin.

Internal protection includes undervoltage lockout (2.70–3.15 V threshold), thermal shutdown at ~150°C junction temperature, and cycle-by-cycle current limiting (3.7–6.0 A switch current limit). The NPN output switch exhibits 0.7–0.9 V saturation voltage at 2.0 A, and feedback pin bias current is ≤800 nA - critical for high-impedance resistor-divider designs.

Key Specifications

Pinout & Package

LM2577T-ADJ/LF02 uses a 5-lead TO-220 (T) package (NS package code T05A), with the tab electrically connected to Pin 2 (Ground). Thermal performance assumes ≥1 in² copper pour on PCB for θ_JA = 65°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-up regulator applications.

Compared with LM2577T-ADJ/LF02, LM2577T-12 offers plug-and-play simplicity at the cost of flexibility, while MC34063AP1G trades peak current capability and thermal robustness for lower cost and higher switching frequency - making it viable only in lighter-load, space-constrained designs.

Availability

LM2577T-ADJ/LF02 is available at Aetrix Electronics and suitable for battery-powered instrumentation, industrial sensor signal conditioning, automotive telematics, and legacy control system retrofits requiring stable component supply and long-term manufacturability.

Supply support for LM2577T-ADJ/LF02 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 and embedded processing technologies, with decades of expertise in power management ICs and industrial-grade reliability.

The LM2577 product line was designed for cost-effective, robust DC/DC conversion in non-isolated boost, flyback, and forward topologies - targeting industrial, automotive, and instrumentation applications demanding high integration and built-in protection.

FAQ

What is the maximum output voltage achievable with LM2577T-ADJ/LF02?

The LM2577T-ADJ/LF02 supports output voltages up to 60 V, limited by its internal switch voltage standoff rating of 65 V and the 10× VIN(min) rule per TI Application Hints. For example, with a minimum input of 3.5 V, the practical upper limit is 35 V - ensuring safe operation within both electrical and thermal constraints of the TO-220 package.

Does LM2577T-ADJ/LF02 require an external diode, and what type is recommended?

Yes, LM2577T-ADJ/LF02 requires an external Schottky or fast-recovery diode connected between the SW pin and output capacitor. A Schottky diode (e.g., 1N5822) with ≤0.5 V forward voltage is preferred for efficiency; fast-recovery types (e.g., UF4007) may be used if reverse voltage exceeds 60 V, though they increase conduction loss and reduce overall efficiency.

How does the soft-start function operate in LM2577T-ADJ/LF02?

The LM2577T-ADJ/LF02 implements soft-start by charging an internal capacitor with a 2.5–9.5 μA current sourced from the COMP pin, gradually increasing the duty cycle over ~1–3 ms. This limits in-rush current into the output capacitor, preventing input supply droop and reducing stress on the NPN switch during startup - especially critical in battery-fed systems.

Can LM2577T-ADJ/LF02 be used in flyback or forward converter topologies?

Yes, LM2577T-ADJ/LF02 is explicitly qualified for flyback and forward converter configurations per its datasheet description and Application Hints. In those topologies, its internal current limit becomes active and protects the switch - unlike in boost mode where external current limiting is required. Transformer-coupled designs enable isolated outputs and higher power density.

What is the thermal derating behavior of LM2577T-ADJ/LF02 in TO-220 package?

With θ_JA = 65°C/W and maximum junction temperature of 125°C (LM2577 grade), LM2577T-ADJ/LF02 must dissipate ≤1.92 W at 25°C ambient to stay within thermal limits. Power dissipation increases with duty cycle and switch losses (I²R_DS(on) + switching losses); above 1.2 W, a small heatsink or ≥1 in² copper pour is mandatory to maintain reliability and output regulation.