Texas Instruments LM2577T-ADJ/LB03

Overview

LM2577T-ADJ/LB03 from Texas Instruments is a monolithic step-up (boost) switching voltage regulator featuring an integrated 3.0A NPN output switch, 52 kHz fixed-frequency oscillator, and adjustable output voltage set via external resistive 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 industrial sensors requiring regulated 5–24V rails from single-cell or multi-cell Li-ion inputs.

For engineers reviewing the LM2577T-ADJ/LB03 datasheet, LM2577T-ADJ/LB03 pinout, LM2577T-ADJ/LB03 application, or LM2577T-ADJ/LB03 equivalent, key selection criteria include its TO-220 (T) package with bent staggered leads, 1.230 V internal reference, soft-start function for in-rush control, and compatibility with standard off-the-shelf boost inductors such as AIE L47–L680 series.

Technical Context

The LM2577T-ADJ/LB03 implements current-mode control architecture, where peak inductor current is directly sensed and compared against an error amplifier output to regulate duty cycle. Its 52 kHz oscillator sets switching frequency independent of external components, simplifying design while enabling predictable EMI behavior.

It uses an internal 1.230 V precision bandgap reference at the feedback (FB) pin, allowing output voltage adjustment from ~1.23 V to 60 V using two external resistors. The NPN switch exhibits 0.7 V typical saturation voltage at 2.0 A, and its current limit threshold is factory-trimmed to 3.7 A minimum (6.0 A absolute max under transient conditions).

Key Specifications

Pinout & Package

LM2577T-ADJ/LB03 is housed in a 5-lead TO-220 package (NS package number T05D) with bent, staggered leads. The exposed tab is electrically connected to Pin 2 (Ground) and serves as the primary thermal path.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2577T-12/LB03, the LM2577T-ADJ/LB03 trades fixed-output simplicity for full voltage adjustability, while MC34063AP1G offers SMT compatibility and higher switching frequency at reduced current capability-making each optimal for distinct power, layout, and thermal constraints.

Availability

LM2577T-ADJ/LB03 is available at Aetrix Electronics and suitable for industrial sensor power supplies, portable medical device rail generation, automotive telematics, and legacy control system retrofits requiring stable component supply and long-term manufacturability.

Supply support for LM2577T-ADJ/LB03 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 expertise in switching regulator design and manufacturing.

The LM2577 product line was engineered for cost-effective, low-component-count DC/DC conversion in industrial, automotive, and battery-powered systems where reliability, thermal robustness, and ease of implementation are critical.

FAQ

What is the minimum input voltage required for stable operation of the LM2577T-ADJ/LB03?

The LM2577T-ADJ/LB03 has a guaranteed minimum operating input voltage of 3.5 V, with undervoltage lockout (UVLO) releasing at 2.70 V minimum. Below 3.5 V, regulation may degrade or cease depending on load and output voltage setting. For reliable start-up and sustained operation, maintain VIN ≥3.5 V under all conditions. The LM2577T-ADJ/LB03 datasheet specifies this as an absolute operating rating.

How is the output voltage set on the LM2577T-ADJ/LB03?

The LM2577T-ADJ/LB03 uses an internal 1.230 V reference connected to the Feedback (FB) pin. Output voltage is set by a resistive divider (R1 from VOUT to FB, R2 from FB to GND), where VOUT = 1.230 × (1 + R1/R2). Standard 1% tolerance resistors are recommended. The LM2577T-ADJ/LB03 reference voltage has ±1.3% initial accuracy over temperature, ensuring tight output tolerance when R1/R2 are precisely selected.

Can the LM2577T-ADJ/LB03 be used in flyback or forward converter topologies?

Yes-the LM2577T-ADJ/LB03 is explicitly designed for step-up (boost), flyback, and forward converter configurations per its datasheet description. In flyback mode, it drives the primary winding with the NPN switch, and energy transfer occurs during switch-off via transformer coupling. The LM2577T-ADJ/LB03's current-mode control and internal protections remain fully functional in these topologies, provided external component ratings (e.g., transformer turns ratio, diode PIV) meet application requirements.

What thermal considerations apply to the LM2577T-ADJ/LB03 in TO-220 (T) package?

The LM2577T-ADJ/LB03 in TO-220 (T) package has θJA = 65°C/W (junction-to-ambient) and θJC = 2°C/W (junction-to-case). To maintain TJ ≤125°C, ensure adequate copper area (≥1 sq in) under the tab and use thermal vias to inner ground planes. At 3.0 A switch current and 0.7 V saturation, power dissipation can reach ~2.1 W-requiring heatsinking for continuous high-load operation. Derating curves in the LM2577T-ADJ/LB03 datasheet define safe operating area vs. ambient temperature.

Does the LM2577T-ADJ/LB03 require an external compensation network?

Yes-the LM2577T-ADJ/LB03 exposes its error amplifier output at the Compensation (COMP) pin, requiring an external RC network (typically 10 kΩ + 100 nF) between COMP and GND to stabilize the control loop. This network sets dominant pole frequency and phase margin. Omitting or mis-sizing this network causes instability, oscillation, or poor transient response. The LM2577T-ADJ/LB03 application notes provide exact values based on inductor value and output capacitance.