Texas Instruments LM340T-5.0/LB01

Overview

LM340T-5.0/LB01 from National Semiconductor is a fixed-output, 3-terminal positive linear voltage regulator delivering 5.0 V ±4% over 0°C to +125°C, with 1 A output current capability, 2.0 V dropout voltage at 1 A, and internal thermal shutdown and short-circuit protection. It is used in local on-card regulation for industrial control power supplies and embedded system rail generation where noise rejection and reliability are critical.

For engineers reviewing the LM340T-5.0/LB01 datasheet, LM340T-5.0/LB01 pinout, LM340T-5.0/LB01 application, or LM340T-5.0/LB01 equivalent, key selection considerations include input voltage range (7.5–20 V), load regulation (≤50 mV over 5 mA–1 A), ripple rejection (62 dB at 120 Hz), quiescent current (8 mA typical), and TO-220 package thermal performance (θ_JA = 54°C/W).

Technical Context

The LM340T-5.0/LB01 implements a monolithic series-pass transistor architecture with internal current limiting, safe-area compensation, and thermal overload protection. Its feedback loop maintains regulated output using an internal bandgap reference and error amplifier, requiring no external compensation.

It operates as a fixed-voltage source without adjustable components but supports external configurations for current limiting or adjustable output via resistor networks. Input bypassing is required only when located >6 inches from the supply filter capacitor; output bypassing (0.1 µF ceramic) improves transient response but is not mandatory for stability.

Key Specifications

Pinout & Package

LM340T-5.0/LB01 uses the 3-lead TO-220 plastic power package (NSC drawing T03B), with metal tab electrically connected to the ground terminal and designed for heatsink mounting.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM7805CT and MC7805CD2TR4, the LM340T-5.0/LB01 trades minor initial accuracy and thermal efficiency for proven field ruggedness, P+ reliability screening, and legacy compatibility in repair and replacement scenarios - making it the preferred choice for maintenance-critical industrial hardware.

Availability

LM340T-5.0/LB01 is available at Aetrix Electronics and suitable for industrial control systems, embedded instrumentation, and test equipment requiring stable component supply, long-lifecycle support, and drop-in replacement capability for legacy National Semiconductor designs.

Supply support for LM340T-5.0/LB01 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

National Semiconductor was a U.S.-based semiconductor company specializing in analog and power management ICs, acquired by Texas Instruments in 2011; its legacy linear regulator portfolio remains widely deployed in industrial infrastructure.

The LM340 series was engineered for rugged, maintenance-free operation in harsh environments - emphasizing thermal resilience, fault tolerance, and long-term parametric stability over ultra-low quiescent current or switching efficiency.

FAQ

What is the maximum input voltage for LM340T-5.0/LB01?

The absolute maximum DC input voltage for LM340T-5.0/LB01 is 35 V, but the recommended operating range is 7.5 V to 20 V to ensure proper regulation and thermal safety. Exceeding 20 V increases power dissipation significantly - for example, at 25 V input and 1 A load, power loss exceeds 20 W, requiring substantial heatsinking beyond TO-220 capabilities. Always verify input transient margins against the 35 V rating.

Does LM340T-5.0/LB01 require an output capacitor for stability?

No, LM340T-5.0/LB01 is internally compensated and does not require an output capacitor for stability. However, a 0.1 µF ceramic capacitor placed directly at the output pin significantly improves transient response to load steps - especially critical in microcontroller or digital logic applications. This capacitor has no effect on DC regulation but reduces output voltage sag during fast current changes.

What is the thermal resistance of LM340T-5.0/LB01 in TO-220 package?

The junction-to-ambient thermal resistance (θ_JA) of LM340T-5.0/LB01 in the TO-220 package is 54°C/W with standard PCB mounting and no heatsink. With a properly mounted heatsink, thermal performance improves dramatically: θ_JC is 4°C/W, so total θ_JA becomes the sum of θ_JC and heatsink-to-ambient resistance. For 1 A operation at 70°C ambient, a 10°C/W heatsink keeps junction temperature below 125°C.

Can LM340T-5.0/LB01 be used in adjustable output configurations?

Yes, LM340T-5.0/LB01 can be configured for adjustable output using external resistors, though it is optimized for fixed 5 V operation. The standard method connects a resistor divider between output and ground, with the adjust node tied to the ground pin - effectively re-biasing the internal reference. Output voltage follows V_OUT = 5 V × (1 + R2/R1), subject to load regulation degradation and reduced current capability compared to fixed mode.

Is LM340T-5.0/LB01 RoHS compliant?

LM340T-5.0/LB01 was manufactured prior to full RoHS enforcement and contains lead in the die attach and leadframe plating. It is not RoHS-compliant per EU Directive 2011/65/EU. For new designs requiring RoHS compliance, consider LM7805CD2TR4 (TO-263, lead-free) or MC7805BD2TR4 as drop-in alternatives with identical electrical behavior and modern environmental certification.