STMicroelectronics LD1085D2M

Overview

LD1085D2M 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 features 1.3 V typical dropout at full load, 5–10 mA quiescent current, and internal thermal/overcurrent protection. Used in industrial power rails where compact high-current regulation and thermal robustness are required.

For engineers reviewing the LD1085D2M datasheet, LD1085D2M pinout, LD1085D2M application, or LD1085D2M equivalent, this page provides verified technical context, real-world design meaning of specifications, validated pin functions, application-specific implementation guidance, and confirmed alternative parts with documented functional and packaging differences.

Technical Context

The LD1085D2M is a monolithic PNP-based adjustable/fixed LDO regulator using on-chip trimming for tight output voltage accuracy. Its reference voltage is internally set to 1.25 V, enabling fixed 3.3 V output via resistor-free configuration. Dropout performance remains stable across temperature and load due to integrated thermal regulation (0.008–0.04 %/W) and current-limiting circuitry.

Unlike traditional PNP regulators, its quiescent current flows into the load rather than being wasted-improving efficiency at light loads. Stability requires only a 10 µF output capacitor, and it maintains ≥60 dB supply voltage rejection at 120 Hz with 3 A load and 25 µF output capacitance.

Key Specifications

Pinout & Package

LD1085D2M is supplied in surface-mount D²PAK (TO-263) package, featuring exposed thermal pad for enhanced heat transfer and mechanical robustness in automated assembly. Pin 1 is Input, Pin 2 is Ground, Pin 3 is Output-pinout matches industry-standard 3-terminal regulators for drop-in replacement in legacy designs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM1085IT-3.3/NOPB, LD1085D2M offers superior thermal performance and surface-mount compatibility; versus TLV1117-33CDR, it delivers double the current capability with integrated thermal protection-making it the only viable choice for 3 A industrial 3.3 V rails in compact D²PAK format.

Availability

LD1085D2M is available at Aetrix Electronics and suitable for industrial automation, embedded controller power, and test equipment requiring stable component supply with guaranteed long-term availability and traceable sourcing.

Supply support for LD1085D2M 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 microcontrollers, power management ICs, and analog/mixed-signal devices for industrial, automotive, and consumer markets.

The LD1085 product line targets high-current, thermally demanding industrial power regulation-designed specifically to replace legacy 78xx and LM1085 regulators with improved dropout, accuracy, and package flexibility.

FAQ

What is the minimum input voltage required for LD1085D2M to regulate 3.3 V at 3 A?

The LD1085D2M requires a minimum input voltage of 4.6 V to maintain regulation at 3 A load, based on its 1.3 V typical dropout voltage (VO + Vd = 3.3 V + 1.3 V). The datasheet specifies 4.9 V as the absolute minimum for guaranteed performance across temperature and process variation-designers should target ≥5.0 V for margin.

Can LD1085D2M be used in adjustable mode despite its fixed 3.3 V marking?

No-LD1085D2M is a factory-trimmed fixed-output variant with internal resistor network; it lacks an ADJ pin and cannot be configured for adjustable output. Only the LD1085V (adjustable version) provides external feedback via ADJ pin; attempting to modify LD1085D2M's output will result in incorrect regulation or instability.

Is a heatsink required for LD1085D2M operating at 3 A continuous current?

A heatsink is recommended but not always mandatory: with R_thJC = 3 °C/W and R_thCA ≈ 40 °C/W on a 2-layer 1-in² copper pad, power dissipation of 3.9 W (at VIN = 9 V) yields ~160 °C junction temperature-exceeding 125 °C rating. A small clip-on heatsink or 4-in² internal copper pour reduces junction temp to safe levels; thermal simulation is advised for each layout.

Does LD1085D2M support reverse-polarity input protection?

No-LD1085D2M has no built-in reverse-voltage protection. Applying negative voltage to the IN pin relative to GND can damage the internal PNP pass transistor. External protection (e.g., series Schottky diode or MOSFET-based ideal diode) is required in systems where input polarity reversal is possible, such as battery-backed or field-wirable industrial terminals.