STMicroelectronics L78L33ACUTR

Overview

L78L33ACUTR from STMicroelectronics is a fixed-output +3.3 V, 100 mA positive linear voltage regulator in SOT-89 package, featuring thermal overload protection, short-circuit current limiting, and no external components required. It delivers stable local regulation for microcontroller I/O rails, sensor power domains, and low-power logic supplies in industrial control modules and portable instrumentation.

For engineers reviewing the L78L33ACUTR datasheet, L78L33ACUTR pinout, L78L33ACUTR application, or L78L33ACUTR equivalent, this page provides verified electrical specs, thermal performance data, real-world use cases, and validated alternative parts for design-in and supply continuity planning.

Technical Context

The L78L33ACUTR employs monolithic bipolar silicon construction with internal current limiting, thermal shutdown, and safe-area protection-enabling robust operation without external protection circuitry. Its output voltage is trimmed to ±4% tolerance (A-grade) at 25 °C and maintains regulation across 1–100 mA load and 5.3–20 V input range.

Designed as a drop-in replacement for Zener-diode/resistor regulators, it reduces quiescent current to 6 mA (typ.) and output noise to 40 µV_RMS (10 Hz–100 kHz), while offering 41–49 dB supply voltage rejection at 120 Hz under 40 mA load.

Key Specifications

Pinout & Package

SOT-89 package: 3-pin surface-mount plastic package with exposed die attach pad for enhanced thermal dissipation; footprint compatible with JEDEC TO-252-2 variant but electrically distinct.

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 and AMS1117-3.3, the L78L33ACUTR delivers superior noise performance (40 µV vs. 30–120 µV) and lower cost in high-volume production, while trading off dropout voltage and quiescent current for robustness in industrial environments with wide input ranges.

Availability

L78L33ACUTR is available at Aetrix Electronics and suitable for industrial sensor nodes, portable medical devices, and smart home controller designs requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for L78L33ACUTR 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, MCU, power, and sensing solutions for automotive, industrial, and consumer markets.

The L78L series belongs to ST's legacy linear regulator product line, engineered for ruggedness, simplicity, and broad compatibility in cost-sensitive embedded systems where reliability under thermal and electrical stress is paramount.

FAQ

What is the maximum allowable input voltage for L78L33ACUTR?

The absolute maximum DC input voltage depends on output voltage: for VO = 3.3 V, VI(max) = 30 V per Table 1. Operation above this risks permanent damage due to junction breakdown. For reliable 3.3 V output, keep VI ≤20 V to maintain specified line regulation and thermal margin.

Can L78L33ACUTR be used in parallel to increase output current?

No-parallel operation is not recommended. The L78L33ACUTR lacks current-sharing features or matching output impedance; unequal thermal gradients cause one device to hog current and trigger thermal shutdown. Use a single higher-current regulator like L78M33 or external pass transistor instead.

Is the SOT-89 package thermally enhanced compared to TO-92?

Yes. The SOT-89 package has R_thJA = 55 °C/W (with 6 cm² copper heatsink), versus 200 °C/W for TO-92. Its exposed die attach pad allows direct thermal coupling to PCB copper, enabling 100 mA continuous operation at ambient temperatures up to 85 °C without additional heatsinking.

Does L78L33ACUTR require input and output capacitors?

Yes-per datasheet Figure 3, a 0.33 µF ceramic capacitor (CI) is mandatory at the input and a 0.1 µF ceramic capacitor (CO) at the output. These stabilize internal feedback, suppress high-frequency oscillation, and improve transient response; omitting either risks instability or excessive output ripple.