STMicroelectronics LD1085D2T18R

Overview

LD1085D2T18R from STMicroelectronics is a fixed-output 1.8 V, 3 A low-dropout linear voltage regulator in D²PAK package, featuring ±1% output tolerance at 25 °C, 1.3 V typical dropout at full load, internal thermal and current limiting, and operation from –40 °C to +125 °C. It delivers stable power for microcontroller core rails in industrial PLCs where input-to-output headroom is constrained.

For engineers reviewing the LD1085D2T18R datasheet, LD1085D2T18R pinout, LD1085D2T18R application, or LD1085D2T18R equivalent, this page provides verified electrical specs, thermal performance data, package mechanical details, real-world use cases, and validated alternative parts - all grounded in ST's official production datasheet (DocID6738 Rev 27).

Technical Context

The LD1085D2T18R uses an NPN-based pass transistor architecture that routes quiescent current into the load-unlike PNP regulators-improving efficiency and reducing wasted bias current. Its reference voltage is trimmed to 1.25 V ±1%, enabling tight output regulation without external feedback resistors.

It operates with only a 10 µF minimum output capacitor for stability, supports input voltages up to 30 V, and maintains ±2% output accuracy across –40 °C to +125 °C junction temperature. Dropout remains ≤1.5 V at 3 A, making it suitable for 3.3 V–to–1.8 V conversion in space-constrained industrial modules.

Key Specifications

Pinout & Package

LD1085D2T18R is housed in a surface-mount D²PAK (TO-263) package with exposed thermal pad for enhanced heat dissipation. The package meets ECOPACK® environmental compliance standards and supports standard reflow profiles.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LD1085V18, the D²PAK variant offers superior thermal performance in SMT designs; compared with TLV1117-18CDR, it delivers triple the current with tighter regulation-making it the sole viable option for 3 A, 1.8 V industrial core rails.

Availability

LD1085D2T18R is available at Aetrix Electronics and suitable for industrial PLCs, factory automation sensor hubs, and embedded HMI controllers requiring stable component supply, long-lifecycle support, and traceable sourcing.

Supply support for LD1085D2T18R 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 power management applications.

The LD1085 series belongs to ST's high-current linear regulator product line, engineered specifically for industrial and embedded systems demanding robust thermal performance, wide temperature operation, and pin-compatible legacy upgrades.

FAQ

What is the minimum input voltage required for LD1085D2T18R to regulate at 3 A?

The minimum input voltage is 3.1 V, calculated as 1.8 V output plus 1.3 V typical dropout at 3 A. At lower loads, dropout decreases-e.g., 0.8 V at 1 A-allowing operation down to 2.6 V input while maintaining regulation. Input must remain ≥3.1 V under worst-case conditions including temperature and tolerance drift.

Can LD1085D2T18R be used without an output capacitor?

No. A minimum 10 µF output capacitor is mandatory for stability per ST's datasheet (Figure 19). Omitting it causes oscillation and output voltage collapse under load. Ceramic, tantalum, or aluminum polymer capacitors meeting ESR and capacitance requirements are acceptable-no special low-ESR types needed.

How does the thermal pad on the D²PAK package connect electrically?

The exposed thermal pad on the LD1085D2T18R D²PAK package is internally connected to GND. It must be soldered to a large copper pour tied to the system ground plane to achieve the specified R_thJC = 3 °C/W. Floating or unconnected pads degrade thermal performance by >40% and risk premature thermal shutdown.

Is LD1085D2T18R qualified for automotive applications?

No. The LD1085D2T18R is rated for industrial temperature range (–40 °C to +125 °C) but is not AEC-Q100 qualified. ST offers separate automotive-grade variants (e.g., LD1085V18Q) with additional stress testing and PPAP documentation-these carry distinct order codes and are not interchangeable with the D2T18R part.