Texas Instruments LM2574N-3.3

Overview

LM2574N-3.3 from Texas Instruments (formerly National Semiconductor) is a monolithic 0.5A step-down (buck) switching voltage regulator in an 8-pin DIP package, delivering a fixed 3.3V output with ±4% tolerance over line and load, 52 kHz fixed-frequency operation, and integrated thermal shutdown and cycle-by-cycle current limiting. It replaces linear regulators in embedded power supplies requiring high efficiency and minimal external components.

For engineers reviewing the LM2574N-3.3 datasheet, LM2574N-3.3 pinout, LM2574N-3.3 application, or LM2574N-3.3 equivalent, key selection considerations include input voltage range (4.75V–40V), guaranteed 0.5A output current, 72% typical efficiency at 12V_IN/0.5A, TTL-compatible shutdown, and compatibility with standard off-the-shelf inductors (e.g., 330 µH).

Technical Context

The LM2574N-3.3 implements a fixed-frequency, current-mode buck topology with internal oscillator, PWM comparator, and NPN power switch. Its control loop uses internal frequency compensation and requires only four external components: input capacitor, output capacitor, catch diode, and inductor.

It operates in continuous conduction mode across its rated load range (0.1A–0.5A) when paired with appropriate inductance (e.g., 330 µH for 12V_IN→3.3V), and transitions to discontinuous mode under light loads. Protection features include thermal shutdown, peak current limiting (1.0A typical), and 50 µA standby current during TTL-driven shutdown.

Key Specifications

Pinout & Package

LM2574N-3.3 is housed in an 8-pin plastic dual in-line package (DIP), NS package code N08A, with Pin 1 designated by notch or dot. Thermal performance is optimized when Pin 3 (Ground) and Pin 5 (Input) are soldered to large PCB copper areas.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2575N-3.3, the LM2574N-3.3 offers lower quiescent current and simpler external component requirements; compared with MP1584EN-LF-Z, it trades higher current and frequency for proven DIP-8 manufacturability and lower EMI sensitivity in noisy industrial environments.

Availability

LM2574N-3.3 is available at Aetrix Electronics and suitable for industrial sensor nodes, embedded microcontroller supplies, POS terminals, and IoT gateway baseboards requiring stable component supply across long-lifecycle programs.

Supply support for LM2574N-3.3 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 acquired National Semiconductor in 2011 and maintains full technical and supply chain support for the SIMPLE SWITCHER™ product family.

The LM2574N-3.3 belongs to TI's SIMPLE SWITCHER™ buck regulator series, designed specifically for cost-sensitive, medium-power DC-DC conversion in industrial, automotive, and consumer applications where ease of use and reliability outweigh ultra-high density or ultra-low IQ requirements.

FAQ

What is the maximum input voltage rating for the LM2574N-3.3?

The LM2574N-3.3 has an absolute maximum input voltage of 45V and a recommended operating maximum of 40V. Exceeding 40V risks violating the device's safe operating area, especially under high ambient temperature or heavy load. The LM2574HV-3.3 variant supports up to 60V input, but the LM2574N-3.3 must remain within its 40V operational limit to ensure reliability and maintain its ±4% output tolerance specification.

Can the LM2574N-3.3 be used with a 5V input source?

Yes, the LM2574N-3.3 supports input voltages as low as 4.75V, making it compatible with regulated 5V sources. However, minimum dropout is determined by duty cycle and switch saturation voltage: at 5V_IN, the achievable output remains 3.3V, but efficiency drops to ~65% and thermal stress increases due to higher conduction losses. For optimal performance, inputs ≥7V are recommended.

Does the LM2574N-3.3 require an external feedback resistor network?

No. The LM2574N-3.3 is a fixed-output version with internal resistor divider connected to the FB pin (Pin 4), which is not externally accessible. Unlike the adjustable LM2574N-ADJ, the LM2574N-3.3 needs no external resistors - Pin 4 remains unconnected on the PCB, simplifying layout and reducing component count.

What inductor value is recommended for the LM2574N-3.3 with a 12V input and 0.5A load?

For 12V input and 0.5A load, the LM2574N-3.3 datasheet specifies a 330 µH inductor (e.g., Pulse Engineering PE-52627 or Renco RL-1284-330). This value ensures continuous conduction mode operation, limits peak inductor current to ~1.0A, and keeps output ripple within acceptable bounds when paired with a 220 µF output capacitor and Schottky catch diode.

Is the LM2574N-3.3 RoHS compliant and lead-free?

Yes, the LM2574N-3.3 is RoHS compliant and lead-free. Texas Instruments confirms that all current production lots meet RoHS Directive 2011/65/EU and JEDEC J-STD-609 standards. The "N" suffix denotes the plastic DIP package, and TI's packaging documentation verifies Pb-free terminations and halogen-free molding compounds for this part number.