STMicroelectronics LD1085V18

Overview

LD1085V18 from STMicroelectronics is a fixed-output 1.8 V, 3 A low-dropout linear voltage regulator in TO-220 package, designed for high-current post-regulation in industrial power supplies and embedded systems. It delivers ±1% output tolerance at 25 °C, 1.3 V typical dropout at full load, and operates across –40 °C to +125 °C junction temperature with internal thermal and current limiting.

For engineers reviewing the LD1085V18 datasheet, LD1085V18 pinout, LD1085V18 application, or LD1085V18 equivalent, this page provides verified technical context, real-world design meaning of key specs, validated pin functions, application-specific implementation value, and confirmed alternative parts with documented functional differences.

Technical Context

The LD1085V18 integrates an NPN-based pass transistor architecture that routes quiescent current into the load-unlike legacy PNP regulators-improving efficiency under light loads. Its reference voltage is trimmed to 1.25 V ±1% (at 25 °C), enabling tight output regulation without external feedback resistors.

Stability requires only a 10 µF output capacitor; no adjustment pin is present since it is a fixed-output variant. Internal protection includes thermal shutdown and current limiting, with dropout voltage decreasing linearly as load current drops below 3 A.

Key Specifications

Pinout & Package

LD1085V18 is supplied in TO-220 package (ECOPACK® compliant), with metal tab electrically connected to the output pin for direct heatsink mounting and low thermal resistance (R_thJC = 3 °C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM1085IT-1.8/NOPB, LD1085V18 offers 0.2 V lower dropout and 30% less quiescent current, improving efficiency in battery-backed systems; versus TLV1117-18CDCYR, it delivers 3.75× more current with ±1% accuracy-making it suitable for high-density industrial control boards where performance and reliability outweigh footprint constraints.

Availability

LD1085V18 is available at Aetrix Electronics and suitable for industrial automation, medical diagnostics equipment, and automotive body electronics requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LD1085V18 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 smart driving, power management, and embedded processing.

The LD1085 series belongs to ST's high-current linear regulator product line, engineered specifically for industrial and automotive-grade power integrity in space- and thermally constrained applications where switching noise is unacceptable.

FAQ

What is the minimum input voltage required for LD1085V18 to maintain regulation at 3 A?

The LD1085V18 requires a minimum input voltage of 3.1 V (1.8 V + 1.3 V dropout) to sustain 3 A output current. At lighter loads, dropout decreases-e.g., ~0.8 V at 1 A-allowing operation from as low as 2.6 V input while maintaining regulation. Input must remain ≤30 V per absolute maximum ratings.

Can LD1085V18 be used without an output capacitor?

No. A minimum 10 µF output capacitor is mandatory for stability, as confirmed in the datasheet's Application Schematic and Typical Characteristics (Figure 19). Omitting it causes oscillation and potential device failure. Tantalum or low-ESR ceramic capacitors are recommended; aluminum electrolytics may require series ESR for phase margin.

Is the metal tab on the TO-220 package electrically connected?

Yes-the metal tab is internally connected to the OUTPUT pin. This enables direct thermal coupling to a heatsink but requires electrical isolation if the heatsink is grounded or referenced to another potential. Insulating kits (mica washers + shoulder washers) or isolated mounting hardware must be used in such cases.

Does LD1085V18 support adjustable output via external resistors?

No. LD1085V18 is a fixed-output variant with internal feedback network set to 1.8 V. Adjustable versions (e.g., LD1085V) exist but require three terminals (ADJ, IN, OUT) and external resistors. The V18 suffix denotes factory-trimmed 1.8 V output-no external components alter the voltage.