STMicroelectronics L7908ACD2T-TR

Overview

L7908ACD2T-TR from STMicroelectronics is a fixed-output, three-terminal negative linear voltage regulator delivering -8 V at up to 1.5 A, featuring thermal overload protection, short-circuit protection, and output transition SOA protection. It operates with input voltages down to -35 V (for -8 V output), supports local on-card regulation in split-supply systems, and is commonly used in industrial power supplies and analog signal conditioning circuits requiring stable negative rail generation.

For engineers reviewing the L7908ACD2T-TR datasheet, L7908ACD2T-TR pinout, L7908ACD2T-TR application, or L7908ACD2T-TR equivalent, key selection criteria include guaranteed -8 V output tolerance (±2%), dropout voltage of 1.1 V at 1 A, junction temperature range (0–125 °C), thermal resistance (R_thJC = 3 °C/W), and D2PAK package compatibility with high-power PCB layouts.

Technical Context

This device implements a monolithic PNP pass transistor architecture with internal current limiting, thermal shutdown, and safe operating area (SOA) protection for sustained load transients. Its feedback loop maintains output regulation across line (VI = -11.5 V to -23 V) and load (IO = -5 mA to -1.5 A) variations while minimizing drift (ΔVO/ΔT = -0.6 mV/°C).

The regulator requires external input (CI ≥ 2.2 µF solid tantalum) and output (CO ≥ 1 µF) capacitors for stability and ripple rejection. It does not require external compensation and supports adjustable configurations via external resistors, though it is optimized for fixed -8 V operation in D2PAK surface-mount form factor.

Key Specifications

Pinout & Package

The L7908ACD2T-TR is housed in a D2PAK (TO-263) surface-mount package with exposed thermal pad for enhanced heat dissipation. Pin assignment follows standard three-terminal negative regulator configuration: Input (IN), Ground (GND), Output (OUT), with GND electrically connected to the thermal pad.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM7908CT and MC7908CD2TG, the L7908ACD2T-TR offers best-in-class thermal resistance (R_thJC = 3 °C/W) for high-current SMT deployment, while maintaining identical regulation accuracy and protection features-making it optimal for space-constrained industrial power modules.

Availability

L7908ACD2T-TR is available at Aetrix Electronics and suitable for industrial power supplies, analog signal conditioning circuits, test equipment, and legacy controller upgrades requiring stable component supply and long-term manufacturability.

Supply support for L7908ACD2T-TR 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 microcontrollers, power ICs, sensors, and discrete components for industrial, automotive, and consumer markets.

The L79xxAC series belongs to ST's legacy linear regulator product line, engineered specifically for robust, cost-effective negative voltage regulation in harsh industrial environments where reliability and thermal resilience are critical.

FAQ

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

The L7908ACD2T-TR requires a minimum input-to-output differential of 1.1 V (dropout voltage) at 1 A load. For guaranteed -8 V regulation, VI must be ≤ -9.1 V. Absolute maximum input is -35 V per datasheet Table 2, but practical operation is limited by power dissipation and thermal design.

Can this regulator be used in adjustable configurations?

Yes-though optimized for fixed -8 V, the L7908ACD2T-TR can be configured as an adjustable negative regulator using two external resistors (per Figure 6 in ST's datasheet). The GND pin becomes the ADJ node, and output voltage is set by VO = -V_REF(1 + R1/R2), where V_REF ≈ 8 V. Stability and load regulation degrade versus fixed mode.

Is a heat sink mandatory for 1.5 A operation?

A heat sink is strongly recommended for continuous 1.5 A operation. At 1.5 A with 10 V input-to-output differential, power dissipation reaches ~15 W. With R_thJC = 3 °C/W and typical R_thCA > 20 °C/W for PCB-only cooling, junction temperature would exceed 125 °C. A low-thermal-resistance heatsink or large copper pour is essential.

Does this part support ceramic output capacitors?

No-ST specifies solid tantalum or aluminum electrolytic capacitors for CO (≥1 µF). Ceramic capacitors are not recommended due to insufficient ESR, which may cause instability or oscillation. If ceramics are used, a 1–2 Ω damping resistor in series with CO is required to meet minimum ESR requirements per application note AN2812.