STMicroelectronics LD1085D2T-R

Overview

LD1085D2T-R from STMicroelectronics is a 3 A low-dropout positive voltage regulator in D²PAK package, delivering fixed 5 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 LD1085D2T-R datasheet, LD1085D2T-R pinout, LD1085D2T-R application, or LD1085D2T-R equivalent, this device is selected for high-current, low-headroom DC-DC post-regulation where quiescent current flows into the load (not wasted), dropout voltage must remain ≤1.5 V at 3 A, and wide-temperature operation with tight initial accuracy is required.

Technical Context

The LD1085D2T-R implements an NPN-based LDO architecture with on-chip trimmed bandgap reference (1.25 V nominal) and error amplifier driving an N-channel pass transistor. Its adjustable variant uses external resistors to set output via the ADJ pin; the D2T-R variant is factory-trimmed for fixed 5 V output, eliminating external feedback components.

Thermal protection activates when junction temperature exceeds ~165 °C, reducing output current to limit dissipation. Dropout voltage remains stable across temperature (–40 °C to +125 °C) and load (0–3 A), with line regulation of ≤10 mV over input range 6.6–20 V at 25 °C and load regulation ≤35 mV across full current range.

Key Specifications

Pinout & Package

LD1085D2T-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 × 15.5 mm × 4.6 mm (L × W × H) and features three terminals compatible with standard 3-terminal adjustable regulators.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2940CT-5.0/NOPB and TPS7A4701RGWR, the LD1085D2T-R uniquely balances 3 A output, 1.3 V dropout, ±1% accuracy, and D²PAK thermal capability - making it optimal for industrial power stages where current, thermal headroom, and simplicity are co-prioritized.

Availability

LD1085D2T-R is available at Aetrix Electronics and suitable for industrial motor control, embedded data acquisition, telecom power management, and legacy system retrofit requiring stable component supply across long product lifecycles.

Supply support for LD1085D2T-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 silicon solutions for automotive, industrial, and consumer markets since 1987.

The LD1085 series belongs to ST's high-current linear regulator product line, engineered specifically for industrial power subsystems demanding robust thermal behavior, wide temperature operation, and drop-in compatibility with legacy 3-terminal regulators.

FAQ

What is the minimum input voltage required for LD1085D2T-R to regulate 5 V at 3 A?

The minimum input voltage is 6.3 V, calculated as 5.0 V + 1.3 V typical dropout. At full load, the device requires at least 6.3 V at the IN pin to maintain regulation; operation below this causes output collapse. Input ripple must stay within ±0.5 V to avoid dropout excursions.

Can LD1085D2T-R be used without an output capacitor?

No - a minimum 10 µF output capacitor is mandatory for stability. Omitting it causes oscillation and potential damage. Ceramic, tantalum, or aluminum electrolytic types are acceptable, but ESR must be between 0.1 Ω and 10 Ω per datasheet Section 4. The capacitor must be placed within 5 mm of the OUT and GND pins.

Does LD1085D2T-R include reverse polarity protection?

No - the device lacks internal reverse-voltage protection. Applying negative voltage to the IN pin relative to GND can damage the IC. An external series Schottky diode (e.g., 1N5822) is required if input polarity reversal is possible in the system, adding ~0.3 V forward drop to the effective dropout.

How does thermal resistance affect maximum power dissipation in D²PAK package?

In D²PAK, R_thJA = 62.5 °C/W (free air) and R_thJC = 3 °C/W. At 3 A with 1.3 V dropout, power dissipation is 3.9 W. With 25 °C ambient and no heatsink, junction temperature reaches 25 + (3.9 × 62.5) ≈ 269 °C - exceeding 125 °C limit. A 25 cm² copper pour reduces R_thJA to ~35 °C/W, yielding T_J ≈ 138 °C; thus a heatsink is mandatory for continuous 3 A operation.