STMicroelectronics LD1085DT-R

Overview

LD1085DT-R from STMicroelectronics is a 3 A low-dropout positive voltage regulator in D²PAK package, delivering fixed 3.3 V output with ±1% tolerance at 25 °C and ±2% over −40 °C to +125 °C. It achieves 1.3 V typical dropout at full load, supports 10 µF minimum output capacitance for stability, and features internal thermal and power limiting for robust operation in industrial power rails.

For engineers reviewing the LD1085DT-R datasheet, LD1085DT-R pinout, LD1085DT-R application, or LD1085DT-R equivalent, this device serves as a high-current, precision fixed-output LDO for embedded power supplies where thermal efficiency, output accuracy, and board-level simplicity are critical - especially when replacing legacy adjustable regulators without redesigning feedback networks.

Technical Context

The LD1085DT-R uses a PNP-based pass transistor architecture with on-chip trimming for tight output voltage accuracy, enabling stable regulation across wide input ranges (4.9 V to 30 V) while maintaining low quiescent current (5–10 mA) that flows into the load rather than being wasted. Its reference voltage is internally set to 1.25 V, eliminating external resistor networks required by adjustable variants.

Thermal protection activates at junction temperatures exceeding +125 °C, and short-circuit current is dynamically limited - dropping from 3.2–4.5 A at low dropout (VI − VO = 5 V) to 0.2–0.5 A at higher differentials (VI − VO = 25 V), ensuring safe fault handling without external current-sense circuitry.

Key Specifications

Pinout & Package

LD1085DT-R is housed in a surface-mount D²PAK (TO-263) package with exposed thermal pad for enhanced heat dissipation. The package measures 10.0 mm × 8.95 mm × 4.6 mm and is RoHS-compliant per ST's ECOPACK® standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LD1085DT-R, LD1085V50 shifts output to 5 V for legacy interface support but retains identical thermal behavior and stability; LD1085D2M33R offers identical performance in tape-and-reel format, enabling seamless transition from prototype (tube) to volume manufacturing without design change.

Availability

LD1085DT-R is available at Aetrix Electronics and suitable for industrial automation, networking infrastructure, and test equipment requiring stable component supply with guaranteed long-term availability and traceable sourcing.

Supply support for LD1085DT-R 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, MCU, power, and sensor solutions for industrial, automotive, and consumer markets.

The LD1085 series belongs to ST's high-current linear regulator product line, engineered specifically for industrial power management where reliability, thermal resilience, and precision output voltage are non-negotiable in extended-temperature deployments.

FAQ

What is the minimum input voltage required for LD1085DT-R to maintain 3.3 V output at 3 A?

The LD1085DT-R requires a minimum input voltage of 4.9 V to sustain 3.3 V output at full 3 A load, based on its 1.3 V typical dropout voltage. At lower loads, dropout decreases - e.g., ~0.8 V at 1 A - allowing operation from as low as 4.1 V in light-load conditions while staying within regulation.

Can LD1085DT-R be used with ceramic output capacitors?

Yes - LD1085DT-R is explicitly characterized for stability with 10 µF ceramic, tantalum, or polymer capacitors. Its internal compensation eliminates the need for high-ESR electrolytic types, enabling smaller footprints and improved transient response without risk of oscillation.

How does the thermal shutdown behave during sustained overload?

When junction temperature exceeds +125 °C, LD1085DT-R disables output and remains off until temperature drops to approximately +110 °C due to built-in hysteresis. This prevents cycling and allows safe cooldown, with no latch-up - normal regulation resumes automatically once thermal limits are cleared.

Is there a recommended heatsink for continuous 3 A operation in still air?

For continuous 3 A operation in still air, ST recommends using the D²PAK's exposed thermal pad with ≥250 mm² copper pour (2 oz. thickness) connected to internal/external ground planes. With this layout, R_thJA is 62.5 °C/W - resulting in ~75 °C rise above ambient at 3 A, staying within the 125 °C max junction limit at ≤50 °C ambient.