STMicroelectronics L78L33CD-TR

Overview

L78L33CD-TR from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 3.3 V output at up to 100 mA, featuring internal current limiting, thermal overload protection, and short-circuit protection. It requires no external components and is rated for ±4% output tolerance (C-grade), with dropout voltage of 2 V and 40 µV RMS output noise (10 Hz–100 kHz). It serves as a low-noise local regulator in microcontroller power domains and sensor interface rails.

For engineers reviewing the L78L33CD-TR datasheet, L78L33CD-TR pinout, L78L33CD-TR application, or L78L33CD-TR equivalent, this device is selected for cost-sensitive, space-constrained embedded systems requiring stable 3.3 V supply with minimal BOM count, low quiescent current (6 mA typ.), and robust fault protection without external pass elements.

Technical Context

The L78L33CD-TR implements a monolithic series-pass regulator architecture with built-in thermal shutdown and foldback current limiting. Its internal bandgap reference and error amplifier maintain output regulation across input voltages from 5.3 V to 20 V and load currents from 1 mA to 100 mA.

It operates over an industrial temperature range (−40 °C to +125 °C) and achieves 41–49 dB supply voltage rejection at 120 Hz. The SO-8 package features pins 2, 3, 6, and 7 internally connected to the die attach flag for enhanced thermal performance when mounted on ≥6 cm² copper pour.

Key Specifications

Pinout & Package

Package: SO-8 (modified internal frame with pins 2, 3, 6, 7 electrically tied to die attach flag for improved thermal resistance; R_thJA = 55 °C/W with 6 cm² copper heat-sink).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MCP1700T-3302E/MB, L78L33CD-TR delivers higher fault resilience at 100 mA loads; compared with AMS1117-3.3, it trades current capacity for simpler protection integration and tighter thermal response without external circuitry.

Availability

L78L33CD-TR is available at Aetrix Electronics and suitable for industrial control panels, IoT edge nodes, and USB peripheral designs requiring stable component supply with guaranteed long-term sourcing and ECOPACK-compliant packaging.

Supply support for L78L33CD-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 silicon solutions for automotive, industrial, and consumer markets since 1987.

The L78L series belongs to ST's legacy linear regulator product line, engineered specifically for cost-effective, robust local regulation in space- and reliability-constrained embedded systems where simplicity and fault tolerance outweigh ultra-low IQ or ultra-low dropout requirements.

FAQ

What is the minimum input voltage required for stable 3.3 V output at 100 mA?

The L78L33CD-TR requires a minimum input voltage of 5.3 V to maintain regulation at 100 mA load, based on its 2 V dropout specification and 3.3 V nominal output. At 40 mA, the dropout is still 2 V, so 5.3 V remains the practical lower limit for full-load operation across temperature.

Can this regulator be used with ceramic output capacitors only?

Yes - the L78L33CD-TR is stable with a minimum 0.1 µF ceramic capacitor on the output and 0.33 µF on the input, as verified in ST's DS0424 test circuits. No ESR requirements or tantalum/Al-elec dependencies apply, enabling compact, high-reliability layouts.

Does the SO-8 package require special PCB layout for thermal performance?

Yes - pins 2, 3, 6, and 7 are internally connected to the die attach flag. To achieve the specified R_thJA of 55 °C/W, these pins must be soldered to ≥6 cm² of 2-oz copper on the PCB. Without this, junction temperature rise may exceed safe limits at 100 mA continuous load.

How does the ±4% output tolerance affect system-level voltage margining?

The ±4% tolerance (3.168–3.432 V at 25 °C) defines worst-case rail deviation before load/temperature effects. Combined with ±30 mV load regulation and ±100 mV line regulation, total output variation remains within ±5.5% - compatible with 3.3 V I/O standards (e.g., LVCMOS, SPI, I²C) across industrial temperature ranges.