STMicroelectronics L78L33ABD-TR

Overview

L78L33ABD-TR from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 3.3 V output at up to 100 mA, with ±4% output tolerance (A-grade), thermal overload and short-circuit protection, and no external components required. It operates across -40°C to +125°C junction temperature and supports local on-card regulation in microcontroller power rails, sensor interfaces, and low-noise analog subsystems.

For engineers reviewing the L78L33ABD-TR datasheet, L78L33ABD-TR pinout, L78L33ABD-TR application, or L78L33ABD-TR equivalent, key selection criteria include its 3.3 V ±4% output accuracy, 2 V dropout voltage, 40 µV RMS output noise (10 Hz–100 kHz), 41–49 dB supply voltage rejection at 120 Hz, and SO-8 package with internally connected thermal flag pins (2, 3, 6, 7).

Technical Context

The L78L33ABD-TR implements a monolithic silicon-based series pass regulator with internal current limiting, thermal shutdown, and safe-area protection-enabling robust operation without external compensation. Its architecture eliminates need for external capacitors beyond standard input/output bypassing (0.33 µF/0.1 µF).

It is designed for fixed-voltage local regulation where low quiescent current (6 mA typ. at 25°C), stable load regulation (≤30 mV over 1–40 mA), and high PSRR (≥41 dB) are critical-particularly in noise-sensitive analog front-ends and embedded control modules powered from unregulated DC sources.

Key Specifications

Pinout & Package

Package: SO-8 (ECOPACK® compliant), with pins 2, 3, 6, and 7 internally bonded to the die attach flag for enhanced thermal performance. External dimensions match standard SO-8; thermal flag requires PCB copper area for effective heat dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM78L33ACZ/NOPB, L78L33ABD-TR offers tighter output tolerance and superior thermal performance in SO-8; versus MCP1700-3302E/TO, it supports higher input voltage and delivers more current-but at higher quiescent power.

Availability

L78L33ABD-TR is available at Aetrix Electronics and suitable for industrial automation, automotive body electronics, medical sensor nodes, and IoT edge gateways requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for L78L33ABD-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 microcontrollers, power management ICs, sensors, and analog chips for industrial, automotive, and consumer markets.

The L78L series belongs to ST's legacy linear regulator product line, engineered specifically for cost-effective, robust local voltage regulation in space- and reliability-constrained embedded systems-emphasizing fault tolerance, ease of use, and wide operating temperature support.

FAQ

What is the minimum input voltage required for stable 3.3 V output?

The L78L33ABD-TR requires a minimum input voltage of 5.3 V to maintain regulation across its full 1–100 mA load range, based on its 2 V dropout voltage specification. At light loads (1–40 mA), regulation holds down to 5.3 V; at 100 mA, input must be ≥5.3 V to sustain 3.3 V output within tolerance.

Can this regulator be used with a 24 V input supply?

Yes-its absolute maximum input voltage is 30 V for VO = 3.3 V, making it compatible with 24 V industrial or automotive supplies. However, power dissipation must be managed: at 100 mA output and 24 V input, PD ≈ (24 − 3.3) × 0.1 = 2.07 W, requiring adequate PCB copper heatsinking per the SO-8 thermal flag design.

Is an input capacitor mandatory?

Yes-a 0.33 µF ceramic capacitor is required between Pin 1 (or Pin 8) and ground, placed as close as possible to the input pins. This prevents oscillation and improves transient response; omission risks instability, especially with long input traces or high-impedance sources.

Does the SO-8 package require special PCB layout considerations?

Yes-pins 2, 3, 6, and 7 are internally connected to the die attach flag and must be soldered to a minimum 6 cm² copper pour on the PCB layer for effective thermal conduction. Without this, R_thJA degrades from 55°C/W to >100°C/W, limiting usable output current to <50 mA at ambient temperatures above 60°C.