STMicroelectronics L78L33ACZTR

Overview

L78L33ACZTR 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 and low-noise analog subsystems.

For engineers reviewing the L78L33ACZTR datasheet, L78L33ACZTR pinout, L78L33ACZTR application, or L78L33ACZTR equivalent, this device serves as a drop-in replacement for Zener/resistor regulators in space-constrained 3.3 V logic supply rails-offering lower quiescent current (6 mA typ.), 40 µV RMS output noise, and 41–49 dB supply voltage rejection at 120 Hz.

Technical Context

The L78L33ACZTR implements a monolithic bipolar linear regulator architecture with built-in foldback current limiting and thermal shutdown circuitry. Its internal design eliminates need for external compensation or bypass capacitors beyond standard input/output decoupling (CI = 0.33 µF, CO = 0.1 µF).

It functions as a fixed-output, single-supply regulator optimized for low-power embedded systems where stable 3.3 V rail integrity is critical. Input-to-output dropout is 2 V, enabling operation from 5.3 V minimum input across full load and temperature range (0–125 °C).

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 and supports lead-free (RoHS-compliant) soldering per ECOPACK2 specification.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM78L33ACZ/NOPB, L78L33ACZTR delivers 40 µV vs. 60–80 µV noise and 41–49 dB vs. 36–45 dB SVR-making it preferable for noise-sensitive analog circuits. Against MCP1700T-3302E/TT, it trades ultra-low IQ for proven ruggedness, thermal shutdown reliability, and TO-92 through-hole compatibility.

Availability

L78L33ACZTR is available at Aetrix Electronics and suitable for industrial control panels, IoT edge sensors, and legacy system upgrades requiring stable component supply, long-lifecycle support, and RoHS-compliant through-hole packaging.

Supply support for L78L33ACZTR 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 power management applications.

L78L33ACZTR belongs to the L78L series of three-terminal positive voltage regulators-engineered for cost-effective, robust local regulation in space-constrained embedded systems where simplicity, reliability, and thermal resilience are prioritized over ultra-low IQ.

FAQ

What is the maximum allowable input voltage for L78L33ACZTR?

The absolute maximum DC input voltage is 30 V when regulating to 3.3 V output. Exceeding this risks permanent damage due to junction breakdown. For reliable operation across temperature and line variations, ST recommends limiting input to ≤25 V with adequate derating margin.

Can L78L33ACZTR be used without input or output capacitors?

No-ST specifies mandatory use of CI ≥ 0.33 µF (ceramic or tantalum) at the input and CO ≥ 0.1 µF (ceramic) at the output for stability and transient response. Omitting either capacitor may cause oscillation, poor load regulation, or thermal runaway under dynamic load conditions.

Does L78L33ACZTR support operation at –40 °C?

No-L78L33ACZTR is rated for 0 to 125 °C junction temperature (AC grade). For –40 °C operation, the AB-grade variant L78L33ABZTR must be selected, which extends the operating junction range to –40 to 125 °C and retains identical electrical specs except for temperature coefficient behavior.

How does thermal performance differ between TO-92 and SO-8 packages of L78L33?

In TO-92, RthJA is 200 °C/W (no heatsink); in SO-8 with 6 cm² copper pour, RthJA drops to 55 °C/W. Thus, TO-92 limits continuous 100 mA operation to ≤50 °C ambient unless heatsinked, while SO-8 enables full-rated current up to 85 °C ambient with proper PCB layout.