STMicroelectronics LD1085DT25R

Overview

LD1085DT25R from STMicroelectronics is a fixed-output 2.5 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 to microcontroller cores, FPGA I/O banks, and industrial sensor signal chains where precision and thermal robustness are critical.

For engineers reviewing the LD1085DT25R datasheet, LD1085DT25R pinout, LD1085DT25R application, or LD1085DT25R equivalent, this page provides verified technical context, real-world design meaning of key specs, validated pin functions, application-specific implementation guidance, and confirmed alternative parts with documented functional trade-offs.

Technical Context

The LD1085DT25R 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% (at 25 °C), enabling tight output regulation across temperature and load.

It requires only a 10 µF output capacitor for stability and supports adjustable configurations via the ADJ pin when used with external resistors. Dropout voltage remains ≤1.5 V up to 3 A output current, allowing operation with minimal input–output differential in space-constrained 5 V or 3.3 V system rails.

Key Specifications

Pinout & Package

LD1085DT25R is supplied in D²PAK (TO-263) surface-mount package with exposed thermal pad for enhanced heat transfer. 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 LD1085DT25R, LM1085IDT-2.5 offers identical package and pinout but looser tolerance and higher dropout, while TLV1117-25CDCYR sacrifices 63% output current capacity and thermal capability for footprint reduction-neither is a drop-in substitute without redesign.

Availability

LD1085DT25R is available at Aetrix Electronics and suitable for industrial automation, motor control, and medical diagnostics requiring stable component supply, long-lifecycle support, and traceable sourcing through STMicroelectronics' qualified production line.

Supply support for LD1085DT25R 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 belongs to ST's high-current linear regulator product line, engineered specifically for industrial and embedded systems demanding robust thermal performance, tight DC accuracy, and compatibility with legacy 3-terminal regulator footprints.

FAQ

What is the minimum input voltage required for LD1085DT25R to regulate at 2.5 V with 3 A load?

The datasheet specifies a maximum dropout voltage of 1.5 V at 3 A. Therefore, the minimum input voltage is 2.5 V + 1.5 V = 4.0 V. In practice, a 4.1 V minimum is recommended to ensure guaranteed regulation across temperature and process variation, as confirmed in Table 4 (VI = 4.1 V min for VO = 2.5 V).

Can LD1085DT25R be used in adjustable mode despite its fixed 2.5 V marking?

No. LD1085DT25R is a factory-trimmed fixed-output variant with internal resistor network connecting the ADJ node to GND and OUT. It lacks the external feedback pins required for adjustment; attempting to reconfigure it as adjustable will result in incorrect or unstable output voltage.

Is a heatsink mandatory for LD1085DT25R operating at 3 A in still air?

Yes. With R_thJA = 62.5 °C/W (D²PAK, no heatsink), 3 A at 1.3 V dropout dissipates 3.9 W, causing a junction-to-ambient rise of 244 °C-far exceeding the 125 °C max. A minimum 25 cm² copper pour with thermal vias or an extruded aluminum heatsink is required to maintain safe junction temperature.

Does LD1085DT25R include reverse-polarity or reverse-current protection?

No. The device has no built-in reverse-voltage or reverse-current blocking. If input polarity may be reversed or if back-driving from downstream circuits is possible, external protection-such as a series Schottky diode or MOSFET-based ideal diode-is required to prevent damage.