onsemi MC79L15ACDR2G: Fixed -15V Linear Voltage Regulator Datasheet and Application Circuit Analysis

The onsemi MC79L15ACDR2G is a classic three-terminal negative voltage regulator designed to deliver a fixed -15V output at currents up to 100mA. As a member of the venerable 79Lxx series, this device is engineered to provide reliable, cost-effective voltage regulation for a wide array of low-power analog and digital circuits. This article delves into the key specifications from its datasheet and analyzes its fundamental application circuit.

Key Datasheet Specifications and Characteristics

Housed in a space-saving SOIC-8 package, the MC79L15ACDR2G is built for automated assembly and offers a compact footprint. Its primary function is to maintain a constant -15V output from an unregulated input voltage that can range from -17V to -35V. This headroom, the voltage difference between input and output, is critical for proper regulation and is formally specified as the dropout voltage.

A paramount feature of any linear regulator is its internal current limiting and thermal shutdown protection. The MC79L15ACDR2G integrates both, safeguarding the device and the load against catastrophic failure from excessive current or overtemperature conditions. Its typical output tolerance is ±5%, ensuring sufficient accuracy for most non-precision applications such as powering op-amp circuits, sensors, and other low-power components requiring a stable negative bias voltage.

The device operates over a junction temperature range of 0°C to +125°C, making it suitable for industrial environments. Furthermore, it does not require external components for stable operation, though they are highly recommended for performance and reliability, as shown in the application circuit.

Standard Application Circuit Analysis

The typical application circuit for the MC79L15ACDR2G is straightforward but requires careful component selection:

1. Input Capacitor (C_IN): A 0.33μF capacitor placed close to the input pin is recommended to improve transient response and bypass high-frequency noise. This is crucial for stability, especially when the regulator is some distance from the power supply filter.

2. Output Capacitor (C_OUT): A 0.1μF capacitor on the output is essential for stability and improved transient response. It prevents the regulator from oscillating under certain load conditions and helps suppress high-frequency noise on the regulated output line.

The circuit operates by dissipating excess power as heat. The power dissipation (P_D) is calculated as P_D = (V_IN - V_OUT) I_LOAD. For example, with an input of -20V, an output of -15V, and a 100mA load, the device would dissipate (5V 0.1A) = 0.5W. This dissipation must be managed to keep the internal junction temperature within its safe operating area (SOA), which may require a heatsink in higher power scenarios.

ICGOODFIND Summary

The onsemi MC79L15ACDR2G is a robust and highly reliable solution for generating a stable -15V supply rail in low-current applications. Its integration of critical protection features like current limiting and thermal shutdown ensures design resilience. While its efficiency is lower than switching alternatives, its simplicity, low noise output, and minimal external component count make it an excellent choice for powering analog circuitry and providing negative voltage references.

Keywords

Linear Regulator

Negative Voltage

Voltage Regulation

Onsemi

Application Circuit