STMicroelectronics L79L09ACUTR

Overview

L79L09ACUTR from STMicroelectronics is a three-terminal fixed negative voltage regulator delivering -9 V output at up to 100 mA, featuring internal current limiting, thermal overload protection, and short-circuit protection. It requires no external components and is specified for operation from -11.5 V to -23 V input, with ±5% output voltage tolerance (AC grade) and 1.7 V dropout voltage. It is used in local on-card regulation for noise-sensitive analog and digital subsystems.

For engineers reviewing the L79L09ACUTR datasheet, L79L09ACUTR pinout, L79L09ACUTR application, or L79L09ACUTR equivalent, this device serves as a drop-in replacement for Zener/resistor regulators in low-noise, low-power negative rail generation-particularly where quiescent current below 6 mA, 70 µV RMS output noise, and 44 dB supply rejection at 120 Hz are critical.

Technical Context

This IC implements a monolithic bipolar linear regulator architecture with built-in thermal shutdown and foldback current limiting. Its fixed -9 V output is stabilized across load currents from 1 mA to 100 mA and input voltages from -11.5 V to -23 V at junction temperatures from 0 °C to 125 °C.

It achieves 40 mV typical load regulation (1–40 mA) and 200 mV line regulation (-11.5 V to -23 V), with 70 µV output noise (10 Hz–100 kHz) and 37–44 dB supply voltage rejection at 120 Hz-enabling stable biasing of op-amps, sensors, and analog front-ends in mixed-signal PCBs.

Key Specifications

Pinout & Package

SOT-89 package: 3-pin surface-mount plastic package with exposed thermal pad (pin 2 = VIN, pin 3 = VOUT, pin 1 = GND); thermal resistance R_thj-amb = 200 °C/W (no heatsink), 55 °C/W with 6 cm² copper pour.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar negative voltage regulation applications.

Compared with LM7909CDT and MC79L09ACP, L79L09ACUTR offers superior thermal performance in SOT-89 (55 °C/W with copper pour), tighter ±5% tolerance than the C-grade alternative, and smaller footprint than TO-220-making it optimal for space-constrained, medium-power analog rails.

Availability

L79L09ACUTR is available at Aetrix Electronics and suitable for industrial sensor nodes, RS-232 interface modules, and audio DAC power supplies requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for L79L09ACUTR 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, power, MCU, and sensor solutions for industrial, automotive, and consumer markets.

L79L09ACUTR belongs to the L79L00 series of three-terminal negative linear regulators, developed specifically for low-power, low-noise local regulation in space-constrained PCBs-replacing Zener/resistor networks with integrated protection and improved stability.

FAQ

What is the minimum input voltage required for L79L09ACUTR to maintain regulation?

The minimum input voltage is -11.5 V under typical conditions (IO = 1–40 mA, TJ = 25 °C). This accounts for the 1.7 V dropout voltage: -9 V output + 1.7 V dropout = -10.7 V minimum, with margin added per datasheet test condition. Below -11.5 V, output voltage drops linearly with input.

Can L79L09ACUTR be used in parallel to increase output current?

No-this device lacks current-sharing capability. Parallel connection risks thermal runaway due to mismatched dropout voltages and thermal coefficients. For higher current, use an external pass transistor configured as a boost stage, or select a higher-current regulator like LM7912 or adjustable LM337 with proper compensation.

Is a heat sink required for continuous 100 mA operation?

At 100 mA with -23 V input, power dissipation is ~1.4 W. In SOT-89 with no PCB copper, R_thj-amb = 200 °C/W yields ΔT ≈ 280 °C-exceeding max junction temperature. With 6 cm² copper pour (R_thj-amb = 55 °C/W), ΔT ≈ 77 °C, keeping TJ < 125 °C if ambient ≤ 48 °C. A small thermal pad is strongly recommended.

What output capacitor value and type are recommended for stability?

A minimum 0.1 µF ceramic capacitor is required at the VOUT pin, placed within 5 mm of the device. For improved transient response and EMI suppression, add a 10 µF tantalum or aluminum electrolytic in parallel. Avoid capacitors with ESR > 1 Ω, as instability may occur with high-ESR types.