STMicroelectronics LD1085D2T33R

Overview

LD1085D2T33R from STMicroelectronics is a fixed-output 3.3 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, FPGA I/O banks, and industrial sensor signal chains requiring tight regulation and high PSRR.

For engineers reviewing the LD1085D2T33R datasheet, LD1085D2T33R pinout, LD1085D2T33R application, or LD1085D2T33R equivalent, this page provides verified technical context, real-world design meaning of key specs, validated pin functions, application-specific implementation guidance, and confirmed alternative options with documented functional trade-offs.

Technical Context

The LD1085D2T33R 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 on-chip to 1.25 V ±1%, enabling precise 3.3 V output via internal resistor divider.

Stability requires only a 10 µF output capacitor; no external adjust resistors are needed for fixed versions. Dropout voltage remains ≤1.5 V across –40 °C to +125 °C and full 3 A load, supported by internal thermal shutdown and short-circuit protection with foldback current limiting.

Key Specifications

Pinout & Package

LD1085D2T33R is housed in a surface-mount D²PAK (TO-263) thermally enhanced package with exposed drain pad for PCB heat sinking. Pin 1 = Input, Pin 2 = Ground, Pin 3 = Output.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TLV1117-33CDCYR and MIC29302WU, the LD1085D2T33R uniquely balances 3 A capability, ±1% accuracy, and 1.3 V dropout in a thermally optimized D²PAK-making it optimal for industrial and test equipment where both current delivery and regulation fidelity are non-negotiable.

Availability

LD1085D2T33R is available at Aetrix Electronics and suitable for industrial automation, medical instrumentation, and test & measurement equipment requiring stable component supply, long-lifecycle support, and traceable sourcing.

Supply support for LD1085D2T33R 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 belongs to ST's high-current linear regulator product line, engineered specifically for industrial power management applications demanding robust thermal behavior, wide temperature operation, and tight DC accuracy without complex external compensation.

FAQ

What is the minimum input voltage required for LD1085D2T33R to maintain regulation at 3 A?

The minimum input voltage is 4.9 V, calculated as V_OUT + V_DROP(max) = 3.3 V + 1.5 V. This ensures regulation under worst-case conditions including temperature extremes and process variation. At room temperature and nominal load, 4.6 V may suffice-but 4.9 V is the guaranteed spec limit per datasheet Table 5.

Can LD1085D2T33R replace adjustable LD1085 variants in existing designs?

No-LD1085D2T33R is a fixed-output variant with internal feedback resistors; it lacks ADJ pin functionality. Replacing an adjustable version requires verifying that the target 3.3 V output matches system requirements and confirming that the D²PAK footprint and thermal layout accommodate the same power dissipation profile.

Is an input capacitor required, and what value is recommended?

Yes-an input capacitor is mandatory for stability and transient response. ST recommends ≥10 µF low-ESR tantalum or ceramic at the IN pin, placed within 5 mm of the device. For high-frequency noise suppression, add a 100 nF ceramic in parallel close to the package.

Does LD1085D2T33R support reverse-voltage protection?

No-the device lacks integrated reverse-battery or reverse-polarity protection. If input reversal is possible in the application, an external series Schottky diode (e.g., 1N5819) must be added between the source and IN pin, accepting its forward voltage drop and power loss.