STMicroelectronics L4940D2T85-TR

Overview

L4940D2T85-TR from STMicroelectronics is a fixed-output 8.5 V, 1.5 A low-dropout linear voltage regulator in D2PAK package, featuring 450 mV typical dropout at 1 A, ±1.5% output voltage accuracy over load/temperature, and integrated thermal shutdown, short-circuit, and reverse-polarity protection. It delivers stable regulation for battery-powered industrial controllers and portable instrumentation where input-to-output headroom is constrained.

For engineers reviewing the L4940D2T85-TR datasheet, L4940D2T85-TR pinout, L4940D2T85-TR application, or L4940D2T85-TR equivalent, key selection criteria include dropout voltage at full load, quiescent current under light-load conditions, output voltage drift versus temperature, and thermal resistance in the D2PAK package for board-level thermal management.

Technical Context

This regulator employs an internal NPN pass transistor with antisaturation circuitry to minimize saturation voltage and achieve low dropout. Its feedback loop maintains output regulation across input voltages from 10.2 V to 17 V and load currents from 5 mA to 1.5 A, with line regulation of ≤9 mV and load regulation of ≤30 mV.

Protection functions are fully integrated: thermal shutdown activates at junction temperatures ≥150 °C; short-circuit current is internally limited to 2.0–2.7 A depending on input voltage; reverse-polarity protection operates down to –15 V input with 180 Ω external resistor.

Key Specifications

Pinout & Package

The L4940D2T85-TR is housed in a surface-mount D2PAK (TO-263) package with exposed thermal pad for enhanced heat transfer. Pin 1 is Input, Pin 2 is Ground, Pin 3 is Output - confirmed per STMicroelectronics Figure 2 (top view) and mechanical drawing P011P6G.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2940CT-8.5/NOPB and TLV1117-85CDR, the L4940D2T85-TR offers superior thermal performance in high-current scenarios, tighter output voltage tolerance (±1.5% vs. ±2%), and proven reverse-polarity resilience - making it optimal for ruggedized, battery-sensitive designs.

Availability

L4940D2T85-TR is available at Aetrix Electronics and suitable for portable medical sensors, industrial PLC I/O modules, automotive body control units, and test & measurement equipment requiring stable component supply with long-term lifecycle support.

Supply support for L4940D2T85-TR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The L4940 series belongs to ST's high-reliability linear regulator product line, engineered specifically for battery-powered and thermally demanding applications where low dropout, robust protection, and long-term parametric stability are critical.

FAQ

What is the minimum input voltage required for regulated 8.5 V output at 1.5 A?

The L4940D2T85-TR requires a minimum input voltage of 9.0 V to maintain regulation at 1.5 A, based on its 450 mV typical dropout voltage. At worst-case 900 mV dropout (per datasheet max), 9.4 V input is needed. Operation below this threshold causes output collapse proportional to (VI – Vd).

Does the D2PAK package require soldering the thermal pad to PCB ground?

Yes - the D2PAK's exposed thermal pad must be soldered to a large copper pour tied to Pin 2 (Ground) to achieve the specified R_thJC = 3 °C/W. Omitting this connection degrades thermal performance by >40%, risking thermal shutdown under sustained 1.5 A load.

Can L4940D2T85-TR replace a 7808 in existing designs?

No - while both provide ~8 V output, the L4940D2T85-TR is a fixed 8.5 V device with different pinout (Input-Ground-Output vs. Input-Ground-Output but reversed physical layout), lower dropout, and stricter input voltage limits (max 17 V vs. 7808's 35 V). Direct replacement requires PCB and schematic revision.

Is external capacitor ESR critical for stability?

Yes - the datasheet specifies a 22 µF low-ESR output capacitor (e.g., tantalum or polymer aluminum). Using high-ESR electrolytics (>100 mΩ) can cause oscillation or poor transient response. Input capacitor must be 0.1 µF ceramic placed within 5 mm of Pin 1.