STMicroelectronics L4940D2T85

Overview

L4940D2T85 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, ±2% output voltage accuracy over load/temperature, and integrated reverse polarity protection, thermal shutdown, and short-circuit current limiting - deployed in battery-powered industrial instrumentation requiring stable 8.5 V rail generation from marginal input headroom.

For engineers reviewing the L4940D2T85 datasheet, L4940D2T85 pinout, L4940D2T85 application, or L4940D2T85 equivalent, key selection criteria include dropout voltage at full load, quiescent current under light-load conditions, output voltage drift versus temperature, and thermal resistance junction-to-case for heatsink-limited PCB layouts.

Technical Context

This device implements a three-terminal monolithic linear regulator architecture with internal current limiting, antisaturation circuitry, and safe-area protection. Its low dropout performance stems from optimized PNP pass transistor design and precision bandgap reference with <1.0 mV/°C output drift.

It operates across −40°C to +150°C junction temperature range with internally limited 2.7 A short-circuit current and 58–66 dB supply voltage rejection at 120 Hz. Reverse input voltage tolerance is −15 V with 100 Ω series resistor, enabling robustness against battery reversal in portable systems.

Key Specifications

Pinout & Package

The L4940D2T85 is housed in a surface-mount D2PAK (TO-263) package with exposed thermal pad for enhanced heat transfer. Pin 1 = Input, Pin 2 = Ground, Pin 3 = 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 and TLV1117-85CDR, the L4940D2T85 delivers superior thermal performance (3 °C/W vs. >50 °C/W), built-in reverse-polarity hardening, and tighter output regulation - making it the optimal choice for industrial battery systems demanding reliability under marginal input conditions.

Availability

L4940D2T85 is available at Aetrix Electronics and suitable for portable instrumentation, industrial sensor transmitters, medical point-of-care devices, and automotive body control modules requiring stable component supply with guaranteed long-term sourcing.

Supply support for L4940D2T85 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 silicon solutions for automotive, industrial, and consumer markets since 1987.

The L4940 series belongs to ST's legacy linear regulator product line, engineered specifically for battery-powered and low-headroom industrial applications where dropout voltage, thermal robustness, and fault resilience are critical.

FAQ

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

The L4940D2T85 requires a minimum input voltage of 9.0 V to maintain regulation at 1.5 A, based on its 500 mV maximum dropout voltage (V_IN = V_OUT + V_DROP = 8.5 V + 0.5 V). Operation below this threshold causes output collapse and unregulated behavior.

Does the L4940D2T85 require an external capacitor on the input pin?

Yes - ST specifies a minimum 0.1 µF ceramic capacitor placed as close as possible to the IN pin to suppress high-frequency noise and prevent oscillation. Larger bulk capacitance (e.g., 10 µF tantalum) may be added upstream for transient response, but the 0.1 µF ceramic is mandatory for stability.

Can the L4940D2T85 be used without a heatsink in a 1.2 A continuous load application?

Yes - with R_θJC = 3 °C/W and R_θCA ≈ 40 °C/W on a 2-layer 1-in² copper pour, power dissipation at 1.2 A and 1 V dropout (1.2 W) yields ~52°C junction rise above ambient. This remains within the −40°C to +150°C operating range, provided ambient stays ≤98°C.

Is the L4940D2T85 qualified for automotive applications?

No - the L4940D2T85 is not AEC-Q100 qualified and lacks automotive-grade screening or extended temperature validation beyond its rated −40°C to +150°C junction range. ST explicitly states non-automotive-grade parts are used in automotive applications at the user's own risk, and it is not recommended for safety-critical or engine-compartment locations.