Overview

The LM2577 (LM2577T-ADJ / LM2577S-ADJ) is a 3A step-up (boost) voltage regulator IC belonging to Texas Instruments' iconic SIMPLE SWITCHER family. It is the step-up counterpart to the ubiquitous LM2596 buck regulator, widely featured on red and green adjustable DC-DC step-up power supply modules across AliExpress, Amazon, and eBay.

Operating over an input voltage range of 3.5V to 40.0V DC, the LM2577 incorporates an internal 3.0A NPN power switch rated for up to 60V DC output, a 52 kHz internal oscillator, soft-start circuitry, and thermal shutdown protection.

Quick reference

Pinout (TO-220-5 Package)

Looking at the front labeled face of the 5-lead package with leads pointing down:

        ┌─────────────┐
        │   O   [TAB] │  (Metal Mounting Tab = GROUND / GND)
        ├─────────────┤
        │   LM2577T   │  (Front Package Face)
        └─┬─┬─┬─┬─┬───┘
          1 2 3 4 5

Output Voltage Formula (Adjustable Version)

The output voltage ($V_{OUT}$) is set by resistor divider $R_1$ (between VOUT and FB) and $R_2$ (between FB and GND):

$V_{OUT} = 1.23\text{V} \times \left(1 + \frac{R_1}{R_2}\right)$

$\text{For } R_2 = 1.0\text{ k}\Omega \text{ and } R_1 = 8.76\text{ k}\Omega \implies V_{OUT} = 12.0\text{ Volts}.$

Common mistakes

• Attempting to step-down ($V_{IN} > V_{OUT}$): The LM2577 is a boost (step-up) converter. Current flows from $V_{IN}$ through the inductor and Schottky diode directly to $V_{OUT}$ even when the IC is idle. If $V_{IN}$ exceeds $V_{OUT}$, the output voltage will equal $V_{IN} - 0.5\text{V}$.
• Omitting the compensation RC network on COMP (Pin 1): Unlike buck regulators, boost converters require loop compensation ($R_C \approx 2.0\text{ k}\Omega$ and $C_C \approx 0.47\ \mu\text{F}$) on Pin 1 to maintain loop stability.

Notes

• LM2577 vs XL6009 vs LM2596: LM2577 is a 52kHz 3A boost regulator; XL6009 is a 400kHz 4A modern boost replacement; LM2596 is a 150kHz 3A step-down (buck) regulator.