Texas Instruments LM340SX-12

Overview

LM340SX-12 from Texas Instruments is a fixed-output +12 V, 1.5-A positive linear voltage regulator in TO-263 (DDPAK) package, featuring internal current limiting, thermal shutdown, and safe-area protection. It delivers stable 12 V output across 5 mA–1.5 A load with ±2% tolerance at 25°C (LM340A-grade spec), supports input voltages up to 35 V, and is used in industrial power supplies and motor driver post-regulation.

For engineers reviewing the LM340SX-12 datasheet, LM340SX-12 pinout, LM340SX-12 application, or LM340SX-12 equivalent, key selection criteria include dropout voltage (2 V at 1 A), line regulation (≤120 mV over 14.5–30 V input), load regulation (≤120 mV over 5 mA–1.5 A), thermal resistance (44.8°C/W junction-to-ambient), and compatibility with standard 0.1-μF ceramic output bypassing.

Technical Context

The LM340SX-12 implements a monolithic three-terminal series pass architecture with built-in foldback current limiting and thermal shutdown triggered at 150°C junction temperature. Its internal safe-area compensation prevents second breakdown during overload, enabling robust operation without external protection circuitry.

It operates as a fixed-voltage regulator with no external feedback required; however, it can be configured for adjustable output or higher current via external pass transistors. Input-to-output differential must remain ≥2 V for regulation, and stability is maintained without mandatory output capacitance-though 0.1-μF ceramic improves transient response.

Key Specifications

Pinout & Package

LM340SX-12 uses a 3-pin DDPAK/TO-263 surface-mount package with exposed thermal pad (pin 2 connected to case). The tab/case is electrically tied to ground, enabling direct PCB thermal coupling.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-output linear regulator applications.

Compared with LM7812CT and LM340T-12, the LM340SX-12 offers superior thermal performance (44.8°C/W vs. 54°C/W) in surface-mount form factor, enabling higher power density and automated assembly-critical for modern industrial control modules where space and reliability are constrained.

Availability

LM340SX-12 is available at Aetrix Electronics and suitable for industrial power supplies, HVAC control units, and brushless DC motor drivers requiring stable component supply with long-term lifecycle support.

Supply support for LM340SX-12 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 company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and communications markets.

The LM340 family was designed specifically for rugged, fixed-output linear regulation in harsh environments-emphasizing thermal resilience, fault tolerance, and minimal external component count for cost-sensitive industrial applications.

FAQ

What is the maximum input voltage rating for LM340SX-12?

The LM340SX-12 has an absolute maximum DC input voltage rating of 35 V. Operation above this level risks permanent damage. For reliable regulation, the minimum input must be at least 14.6 V to maintain line regulation at full load-ensuring the 2-V dropout requirement is met across temperature and load variations. Always verify input transient margins in real-world systems.

Does LM340SX-12 require an output capacitor for stability?

No, the LM340SX-12 is internally compensated and remains stable without any output capacitor. However, adding a 0.1-μF ceramic capacitor at the output significantly improves transient response to fast load changes-a recommended practice for motor driver or microcontroller power domains. This capacitor does not affect stability but enhances dynamic performance.

What thermal considerations apply to LM340SX-12 in TO-263 package?

The LM340SX-12 in TO-263 has a junction-to-ambient thermal resistance (θ_JA) of 44.8°C/W with standard PCB layout. To avoid thermal shutdown at 1.5 A, power dissipation must stay below ~2.8 W (assuming 25°C ambient), requiring ≥1 in² copper pour under the thermal pad. Derate output current if ambient exceeds 70°C or heatsinking is limited-always monitor junction temperature using θ_JC = 1.5°C/W and case temperature measurement.

Can LM340SX-12 be used in adjustable-output configurations?

Yes, the LM340SX-12 can be adapted for adjustable output using external resistive feedback networks or pass transistors-as documented in TI's LM340 datasheet Figure 21 (adjustable regulator) and Figure 24 (high-current extension). While its native function is fixed +12 V, the underlying architecture supports modification for non-standard voltages or higher current, provided stability and thermal limits are validated per application.

How does LM340SX-12 handle short-circuit conditions?

The LM340SX-12 incorporates foldback current limiting and thermal shutdown. Under output short, it limits current to ~1.5 A (typical), reducing to lower values as junction temperature rises. If sustained, thermal shutdown activates at 150°C, halting output until cooldown. Once cooled, it auto-restarts-enabling robust recovery in intermittent fault scenarios like wiring shorts in HVAC field installations.