STMicroelectronics L78L33ACD13TR

Overview

L78L33ACD13TR 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, supports input voltages up to 30 V (for 3.3 V output), and is specified for operation from 0 °C to 125 °C junction temperature - ideal for local regulation in microcontroller power domains and low-noise sensor supply rails.

For engineers reviewing the L78L33ACD13TR datasheet, L78L33ACD13TR pinout, L78L33ACD13TR application, or L78L33ACD13TR equivalent, this device serves as a drop-in replacement for Zener-diode/resistor regulators with lower quiescent current (6 mA typ.), tighter output tolerance (±4% over temperature), and improved ripple rejection (41–49 dB at 120 Hz).

Technical Context

The L78L33ACD13TR 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 operates across an input range of 5.3 V to 20 V for stable 3.3 V output, maintains load regulation within ±30 mV (1–40 mA) and line regulation within ±100 mV (6.3–20 V), and delivers 40 µV RMS output noise (10 Hz–100 kHz) - enabling use in noise-sensitive analog and mixed-signal subsystems.

Key Specifications

Pinout & Package

Supplied in SO-8 package with internal thermal enhancement: pins 2, 3, 6, and 7 are electrically connected to the die attach flag for reduced R_thJC (20 °C/W max). This configuration 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 LM317LZ and TLV73333PDBVR, the L78L33ACD13TR offers superior fault resilience (thermal + short-circuit protection), higher output current headroom (100 mA), and tighter initial accuracy (±4%) - making it optimal for cost-sensitive industrial and automotive-adjacent embedded systems requiring proven reliability without design overhead.

Availability

L78L33ACD13TR is available at Aetrix Electronics and suitable for industrial sensor nodes, USB-C peripheral power management, and programmable logic controller I/O modules requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for L78L33ACD13TR 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 - emphasizing simplicity, fault tolerance, and wide-temperature operation.

FAQ

What is the maximum allowable input voltage for L78L33ACD13TR?

The absolute maximum DC input voltage is 30 V when regulating to 3.3 V output, as specified in Table 1 of DS0424 Rev 30. Exceeding this risks permanent damage due to internal junction breakdown, even with thermal protection active. For reliable operation, keep VI ≤ 20 V under full load per electrical characteristics tables.

Can L78L33ACD13TR be used in place of a 3.3 V Zener diode + resistor?

Yes - the L78L33ACD13TR replaces Zener/resistor networks with superior performance: tighter output tolerance (±4% vs. ±5–10%), lower quiescent current (6 mA vs. resistor-based bias current), and inherent short-circuit/thermal protection. No redesign is needed beyond swapping footprints and verifying SO-8 thermal pad layout.

Does L78L33ACD13TR require input and output capacitors?

Yes - ST specifies a minimum 0.33 µF ceramic capacitor at the input and 0.1 µF ceramic capacitor at the output for stability and transient response. Omitting either degrades load regulation, increases noise, and may cause oscillation under dynamic load conditions per Figure 15 and test circuit notes in DS0424.

How does the SO-8 thermal flag configuration affect PCB layout?

Pins 2, 3, 6, and 7 are internally connected to the die attach flag, forming a low-thermal-resistance path to PCB copper. To achieve rated R_thJA = 55 °C/W, ST requires ≥6 cm² of 2-oz copper connected directly to these pins. Isolating or undersizing this copper area causes junction temperature rise and premature thermal shutdown.