LM2576 — 3A 52kHz Step-Down (Buck) Switching Regulator

Overview

The LM2576 (and adjustable TO-220 5-pin variant LM2576T-ADJ) is a 3.0 Amp step-down (buck) switching regulator IC manufactured by Texas Instruments (originally National Semiconductor). Operating at a $52\text{ kHz}$ switching frequency, it is the direct predecessor to the ubiquitous LM2596 ( $150\text{ kHz}$ ).

Because of its lower switching frequency, the LM2576 uses larger inductors (typically $100\ \mu\text{H}$ to $330\ \mu\text{H}$ ) than modern high-frequency converters, but offers exceptional ruggedness, internal current limiting, and thermal shutdown features. It is widely used in power supplies, industrial control circuits, and hobbyist DC-DC step-down converters.

Quick reference


Regulator Type	Monolithic Step-Down (Buck) Switching Regulator
Package	TO-220-5 (Through-Hole) / TO-263-5 (D2PAK)
Input Voltage Range ( $V_{IN}$ )	$4.0\text{ V}$ to $40.0\text{ V}$ DC (HV version up to $60\text{ V}$ )
Output Voltage Range ( $V_{OUT}$ )	$1.23\text{ V}$ to $37.0\text{ V}$ DC (Adjustable) / Fixed 3.3V, 5V, 12V, 15V
Continuous Output Current ( $I_{OUT}$ )	Up to $3.0\text{ A}$
Switching Frequency	$52\text{ kHz}$ internal oscillator
Conversion Efficiency	$75\% \dots 88\%$
Control Features	`ON`/`OFF` logic shutdown pin (Low = ON, High = OFF)

Pinout (TO-220 5-Pin Package)

text

        ┌──────────────────┐
        │   LM2576T-ADJ    │  (Front Package Face)
        └─┬───┬───┬───┬────┘
          1   2   3   4   5
         VIN SW  GND FB  ON/OFF

Pin	Name	Description
1	`VIN`	Unregulated DC input supply pin (+4.0 V to +40 V DC)
2	`OUTPUT` / `SW`	Internal NPN power switch emitter output (Connects to Schottky catch diode & 100µH inductor)
3	`GND`	Ground reference (0 V)
4	`FEEDBACK` / `FB`	Feedback sensing pin (1.23V internal reference for ADJ version)
5	`ON`/`OFF`	Logic control shutdown input (Connect to GND for normal operation, High to shut down)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Input Voltage Range	$V_{IN}$	4.0	12 / 24	40	V	Standard version ( $V_{IN} - V_{OUT} \ge 2.0\text{V}$ )
Feedback Reference Voltage	$V_{FB}$	1.193	1.230	1.267	V	Adjustable version ( $V_{IN} = 12\text{V}, I_{OUT} = 0.5\text{A}$ )
Continuous Load Current	$I_{OUT}$	—	3.0	—	A	$V_{IN} - V_{OUT} \ge 2.0\text{V}$
Peak Current Limit	$I_{CL}$	4.2	5.8	6.9	A	Internal switch current limit
Oscillator Frequency	$f_{OSC}$	47	52	58	kHz	Internal clock frequency
Quiescent Current	$I_Q$	—	5.0	10.0	mA	Operating state ( $V_{FB} = 1.3\text{V}$ )
Standby Current	$I_{STBY}$	—	50	200	$\mu\text{A}$	Shutdown state ( $V_{ON/OFF} = 5.0\text{V}$ )

Typical Application Circuit

text

       +V_IN (4.0V - 40V DC Input)
          │
       [Pin 1: VIN]
        LM2576T-ADJ ── [Pin 2: SW] ─── [ 100µH Inductor ] ──┬─── +V_OUT Regulated DC Output
          │                                  │              │
       [Pin 3: GND]               [1N5822 Schottky Diode] [ R1 = 1kΩ ]
          │                                  │              │
         GND ────────────────────────────────┴──────────────┼─── [Pin 4: FB]
                                                            │
                                                          [ R2 ]
                                                            │
                                                           GND

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

Common mistakes

Using a standard silicon rectifier diode instead of a Schottky diode: The LM2576 requires a fast Schottky catch diode (such as 1N5822 or SR360) between SW and GND. Standard 1N4007 diodes are too slow and cause overheating and failure.
Undersized inductor value: Due to the $52\text{ kHz}$ switching frequency, using smaller inductors (such as 10µH or 22µH meant for 1MHz+ switchers) leads to excessive peak currents and regulator saturation. Use $100\ \mu\text{H}$ or higher rated for 3A continuous.

Notes

LM2576 vs LM2596: LM2576 operates at $52\text{ kHz}$ , requiring larger inductors ( $100\ \mu\text{H}$ ), whereas LM2596 operates at $150\text{ kHz}$ with smaller inductors ( $33\ \mu\text{H}$ ).

Interface	5-Terminal Switching Output
Package	TO-220-5 / TO-263-5 (D2PAK)