STMicroelectronics L78L08ACUTR

Overview

L78L08ACUTR from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 8 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 35 V (for 8 V output), and exhibits ±4% output voltage tolerance (A-grade) with 1.7 V dropout at 40 mA. It is used for local on-card regulation in microcontroller power rails, sensor interface supplies, and low-power industrial control modules.

For engineers reviewing the L78L08ACUTR datasheet, L78L08ACUTR pinout, L78L08ACUTR application, or L78L08ACUTR equivalent, this device serves as a drop-in replacement for legacy 78L08 regulators in space-constrained designs requiring stable 8 V biasing with minimal BOM count and robust fault protection.

Technical Context

The L78L08ACUTR implements a monolithic silicon-based series pass transistor architecture with built-in thermal shutdown and foldback current limiting. Its regulation loop maintains output stability across load currents from 1 mA to 100 mA and input voltages from 10.5 V to 23 V, with line regulation of 125 mV (typ.) and load regulation of 40 mV (max) over temperature.

It operates within a junction temperature range of 0 °C to 125 °C (L78LxxAC grade), delivers 60 µV RMS output noise (10 Hz–100 kHz), and achieves 37–45 dB supply voltage rejection at 120 Hz - enabling clean DC biasing in analog signal chains and mixed-signal subsystems.

Key Specifications

Pinout & Package

Supplied in SOT-89 package: compact surface-mount outline with exposed die attach pad for enhanced thermal dissipation. Pin 1 = Input, Pin 2 = Ground, Pin 3 = Output.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM78L08ACZ/NOPB and MC78L08ACP, the L78L08ACUTR offers tighter output tolerance, lower noise, superior supply rejection, and guaranteed 100 mA delivery in a thermally efficient SOT-89 package - making it optimal for modern compact, noise-critical, and thermally constrained designs.

Availability

L78L08ACUTR is available at Aetrix Electronics and suitable for industrial sensor interfaces, microcontroller power rails, IoT edge node power, and programmable logic supplies requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for L78L08ACUTR 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 industrial, automotive, and consumer markets.

The L78L series belongs to ST's legacy linear regulator product line, engineered specifically for cost-effective, robust, and easy-to-use fixed-voltage regulation in space- and reliability-constrained embedded systems.

FAQ

What is the minimum input voltage required for stable 8 V output?

The L78L08ACUTR requires a minimum input voltage of 10.5 V to maintain regulation across all load and temperature conditions, based on its 1.7 V dropout specification at 40 mA and worst-case 2.0 V dropout at 100 mA. Below 10.5 V, output voltage drops linearly with input.

Can this regulator be used with ceramic output capacitors?

Yes - the L78L08ACUTR is stable with ceramic output capacitors ≥0.1 µF, as confirmed in ST's DS0424 test circuits. No ESR requirements apply, unlike older 78xx regulators; this simplifies layout and improves transient response in high-frequency load switching.

Does the SOT-89 package require a heatsink pad on the PCB?

Yes - the SOT-89 package uses Pin 2 (GND) as the thermal flag; ST recommends connecting it to a ≥1 cm² copper pour for optimal thermal performance. Without this, junction temperature may exceed 125 °C at >60 mA continuous load, triggering thermal shutdown.

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

The ±4% tolerance (7.68–8.32 V at 25 °C) ensures compatibility with 8 V-rated peripherals having ≥±5% supply margin. For precision references, pair with a low-dropout post-regulator or use the output to drive a resistive divider into an ADC - system-level calibration compensates residual error.