STMicroelectronics L78L33ACZ

Overview

L78L33ACZ 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, operates with input voltages up to 30 V (for 3.3 V output), and maintains ±4% output tolerance over 0–125 °C junction temperature. It is used for local on-card regulation in microcontroller power domains, sensor interface rails, and low-noise analog subsystems.

For engineers reviewing the L78L33ACZ datasheet, L78L33ACZ pinout, L78L33ACZ application, or L78L33ACZ equivalent, key selection considerations include dropout voltage (2 V), quiescent current (6 mA at 25 °C), output noise (40 µV RMS, 10 Hz–100 kHz), supply voltage rejection (41–49 dB at 120 Hz), and thermal shutdown behavior under sustained load.

Technical Context

The L78L33ACZ employs a monolithic bipolar architecture with built-in foldback current limiting and thermal shutdown circuitry, enabling robust operation without external protection components. Its internal reference and error amplifier maintain regulation across line (VI = 5.3–20 V) and load (IO = 1–100 mA) variations while sustaining stable output under transient conditions.

It functions as a fixed-output series pass regulator with a PNP-type pass transistor, requiring only input and output capacitors (CI = 0.33 µF, CO = 0.1 µF) for stability. The device's 2 V dropout voltage defines minimum headroom needed between input and regulated output, and its 40 µV output noise supports noise-sensitive analog circuits such as ADC references and low-power RF front-ends.

Key Specifications

Pinout & Package

Supplied in TO-92 package (3-pin, through-hole), with standardized pinout: Pin 1 = Input, Pin 2 = Ground, Pin 3 = Output. The package uses epoxy-molded plastic construction with lead-free (RoHS-compliant) terminations and ECOPACK2 environmental grade.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM78L33ACZ, L78L33ACZ delivers superior PSRR and lower noise at modest quiescent cost; versus MCP1700-3302E, it trades ultra-low IQ and low dropout for proven ruggedness, thermal flagless shutdown, and direct TO-92 footprint compatibility.

Availability

L78L33ACZ is available at Aetrix Electronics and suitable for industrial sensor nodes, microcontroller power domains, IoT peripheral rails, and legacy system retrofits requiring stable component supply and long-term manufacturability.

Supply support for L78L33ACZ 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 automotive, industrial, and consumer markets.

The L78L series belongs to ST's legacy linear regulator product line, engineered for reliability, ease of use, and robustness in harsh environments-targeting applications where simplicity, thermal resilience, and long-lifecycle support outweigh ultra-low-power or ultra-low-dropout requirements.

FAQ

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

The L78L33ACZ requires a minimum input voltage of 5.3 V to maintain regulation across full load (1–100 mA) and temperature (0–125 °C), based on its 2 V dropout specification and ±4% output tolerance. Below 5.3 V, output voltage drops linearly with input, and regulation ceases.

Can L78L33ACZ be used in parallel to increase output current?

No-L78L33ACZ is not designed for parallel operation. Its output voltage tolerance (±4%) and lack of current-sharing control cause unequal load distribution, risking thermal runaway in one device. For >100 mA, use a single higher-current regulator or add an external pass transistor per Figure 13 in DS0424.

Is a heat sink required for continuous 100 mA operation?

A heat sink is not required for 100 mA at room temperature with adequate PCB copper (≥6 cm²), as RthJA is 200 °C/W for TO-92. At 100 mA and 30 V input, power dissipation reaches 2.67 W, raising junction temperature by ~534 °C-exceeding safe limits. Derate to ≤40 mA at high VI or use SO-8 variant with thermal pad.

Does L78L33ACZ support reverse-polarity input protection?

No-L78L33ACZ has no internal reverse-voltage protection. Applying negative voltage to Pin 1 relative to Pin 2 can damage the IC. External protection (e.g., series diode or MOSFET-based ideal diode) is required in systems prone to battery reversal or incorrect insertion.