STMicroelectronics LD1085CDT-R

Overview

LD1085CDT-R from STMicroelectronics is a 3 A low-dropout adjustable positive voltage regulator in DPAK package, featuring ±2% output voltage tolerance at 25 °C, 1.3 V typical dropout at 3 A, and internal thermal/power limiting. It delivers stable regulated output across -40 °C to +125 °C and is used in industrial power supplies where high current and tight regulation are required.

For engineers reviewing the LD1085CDT-R datasheet, LD1085CDT-R pinout, LD1085CDT-R application, or LD1085CDT-R equivalent, key selection criteria include dropout voltage at full load, adjust pin current stability, line/load regulation performance, thermal resistance (R_thJC = 3 °C/W), and compatibility with standard 3-terminal adjustable regulator layouts.

Technical Context

The LD1085CDT-R employs an NPN-based pass transistor architecture-unlike PNP regulators-so quiescent current flows into the load, improving efficiency. Its on-chip trimming enables ±2% reference voltage accuracy (1.25 V nominal) over temperature and load.

It requires only a 10 µF output capacitor for stability and supports adjustable output via external resistors (V_O = V_REF(1 + R₂/R₁)). Dropout decreases with load, guaranteeing ≤1.5 V at 3 A and maintaining regulation down to VI – VO ≥ 1.3 V.

Key Specifications

Pinout & Package

Supplied in DPAK (TO-252-3) surface-mount package with exposed thermal pad for enhanced heat dissipation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar adjustable LDO regulator applications.

Compared with LM317LDG-TR and TLV1117-33CDCYR, the LD1085CDT-R uniquely combines 3 A capability, 1.3 V dropout, ±2% reference accuracy, and DPAK thermal performance-making it the only option among the three qualified for high-current, thermally demanding industrial LDO applications.

Availability

LD1085CDT-R is available at Aetrix Electronics and suitable for industrial PLC power rails, telecom line card supplies, test & measurement equipment, and motor drive control boards requiring stable component supply and long-term manufacturability.

Supply support for LD1085CDT-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 power management applications.

The LD1085C belongs to ST's high-current linear regulator product line, engineered specifically for industrial and telecom systems needing robust, adjustable, high-accuracy voltage regulation in thermally constrained surface-mount packages.

FAQ

What is the minimum output capacitor required for stability?

The LD1085CDT-R requires a minimum 10 µF output capacitor (tantalum or aluminum electrolytic) for guaranteed stability across all operating conditions. Ceramic capacitors may be used if ≥22 µF and series ESR ≥ 0.1 Ω is added; otherwise, oscillation risk increases due to low ESR.

Can LD1085CDT-R replace LM317 in existing designs?

Yes-LD1085CDT-R is pin-to-pin compatible with LM317 in DPAK footprint and uses identical 3-terminal adjustable configuration. However, its lower dropout (1.3 V vs. ~2 V), tighter reference tolerance (±2% vs. ±4%), and higher current rating (3 A vs. 1.5 A) require verification of thermal margin and input voltage headroom.

Does LD1085CDT-R require an input capacitor?

An input capacitor is recommended but not strictly mandatory: ≥1 µF tantalum or 10 µF aluminum electrolytic placed near the input pin reduces high-frequency noise and improves transient response. Without it, line rejection degrades above 10 kHz and startup overshoot may increase.

How does thermal shutdown behave during overload?

When junction temperature exceeds ≈160 °C, internal thermal protection disables the pass transistor until temperature falls by ~20 °C. Recovery is automatic and non-latching. During repeated cycling, average output current drops significantly-designers must ensure heatsinking keeps T_J < 140 °C under worst-case load and ambient.