STMicroelectronics L78L09ABZ

Overview

L78L09ABZ from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 9 V output at up to 100 mA, featuring internal current limiting, thermal shutdown, and short-circuit protection. It operates across an input voltage range of 11.5–23 V with ±4% output tolerance (AB grade), supports industrial temperature range (−40 °C to +125 °C), and requires no external components for basic operation - commonly used in local on-card regulation for microcontroller power rails and sensor interface circuits.

For engineers reviewing the L78L09ABZ datasheet, L78L09ABZ pinout, L78L09ABZ application, or L78L09ABZ equivalent, this device is selected for low-noise, cost-sensitive 9 V supply generation where dropout voltage (1.7 V), quiescent current (6 mA at 25 °C), and supply voltage rejection (37–44 dB at 120 Hz) are critical design constraints.

Technical Context

The L78L09ABZ implements a monolithic series pass transistor architecture with built-in foldback current limiting and thermal overload protection, enabling robust operation without external safety circuitry. Its AB-grade specification ensures guaranteed performance over −40 °C to +125 °C junction temperature, and its SO-8 package variant integrates pins 2, 3, 6, and 7 to the die attach flag for enhanced thermal dissipation.

It achieves 40 µV typical output noise (10 Hz–100 kHz), load regulation of ≤40 mV (1–40 mA), and line regulation of ≤150 mV (VI = 12–23 V), making it suitable for noise-sensitive analog front-ends and mixed-signal systems requiring stable local regulation.

Key Specifications

Pinout & Package

Available in TO-92 (3-pin) and SO-8 (8-pin) packages; L78L09ABZ specifically uses the SO-8 variant with pins 2, 3, 6, and 7 internally connected to the die attach flag for improved thermal performance. Standard pinout applies: Pin 1 = Input, Pin 2 = Ground, Pin 3 = Output (with additional thermal/ground pins per SO-8 layout).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM78L09ACZ and MC78L09ABDR2G, the L78L09ABZ offers superior thermal specification coverage, tighter output tolerance, and better supply ripple rejection - making it the preferred choice for new designs requiring guaranteed performance across harsh environments and noise-sensitive loads.

Availability

L78L09ABZ is available at Aetrix Electronics and suitable for microcontroller power supplies, sensor signal conditioning, IoT edge nodes, and legacy system voltage translation requiring stable component supply and long-term industrial lifecycle support.

Supply support for L78L09ABZ 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 for cost-effective, robust local regulation in resource-constrained embedded systems - emphasizing reliability, ease of use, and broad temperature compliance over high-efficiency switching.

FAQ

What is the minimum input voltage required for L78L09ABZ to maintain regulation?

The L78L09ABZ requires a minimum input-to-output differential of 1.7 V (typical dropout voltage) to sustain regulation. With a nominal 9 V output, this means the input must be ≥10.7 V under typical conditions. At maximum load (100 mA) and elevated temperature, the dropout may rise slightly, so 11.5 V is the guaranteed minimum input per datasheet test conditions.

Can L78L09ABZ be used in parallel to increase output current?

No - the L78L09ABZ is not designed for parallel operation. Its output voltage tolerance (±4%) and lack of current-sharing features mean unequal load distribution would occur, risking thermal runaway in one device. For >100 mA, use a higher-current regulator (e.g., L7809CD2T) or add an external pass transistor per Figure 14 in the datasheet.

Is a heat sink required for SO-8 packaged L78L09ABZ?

A dedicated metal heat sink is not required, but the SO-8 package demands ≥6 cm² of copper pour connected to pins 2, 3, 6, and 7 on the PCB to achieve the rated R_thJA of 55 °C/W. Without this copper area, thermal resistance rises sharply, limiting safe power dissipation to ~0.3 W at 25 °C ambient.

Does L78L09ABZ require input/output capacitors, and what values are recommended?

Yes - a 0.33 µF ceramic capacitor is required at the input and a 0.1 µF ceramic capacitor at the output, placed as close as possible to their respective pins. These stabilize internal feedback and suppress high-frequency oscillation; tantalum or electrolytic caps are not recommended due to ESR-related instability risks.