STMicroelectronics LD1085DT33R

Overview

LD1085DT33R 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 powers microcontroller core rails, FPGA I/O banks, and industrial sensor signal chains requiring stable low-noise DC supply.

For engineers reviewing the LD1085DT33R datasheet, LD1085DT33R pinout, LD1085DT33R application, or LD1085DT33R equivalent, key selection criteria include dropout voltage at 3 A, output tolerance over temperature, quiescent current behavior under load, and thermal resistance (R_thJC = 3 °C/W) for heatsink-limited PCB layouts.

Technical Context

The LD1085DT33R uses an NPN-based pass transistor architecture that routes quiescent current into the load-unlike PNP regulators-improving efficiency and reducing no-load power loss. Its internal bandgap reference (1.25 V) and error amplifier enable tight regulation without external feedback resistors.

Stability requires only a 10 µF output capacitor (tantalum or ceramic), and the device maintains regulation with input voltages as low as 4.9 V at 3 A output. Short-circuit protection limits current to 3.2–4.5 A depending on dropout voltage, while thermal shutdown activates at junction temperatures exceeding 165 °C.

Key Specifications

Pinout & Package

LD1085DT33R is housed in a surface-mount D²PAK (TO-263) package with exposed thermal pad for enhanced heat transfer. The package measures 10.0 × 8.95 × 4.6 mm and features gull-wing leads compatible with standard reflow profiles.

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, LD1085DT33R delivers tighter regulation and superior thermal protection; versus TLV1117-33IDCYR, it provides 3.75× higher current and 4× better thermal resistance-making it the sole viable choice for industrial 3 A loads requiring long-term reliability.

Availability

LD1085DT33R is available at Aetrix Electronics and suitable for industrial automation controllers, medical diagnostic equipment, automotive body electronics, and networking infrastructure requiring stable component supply across extended temperature ranges and multi-year production cycles.

Supply support for LD1085DT33R 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 and automotive applications demanding robust thermal performance, wide operating temperature range, and minimal external components.

FAQ

What is the minimum input voltage required for LD1085DT33R to maintain regulation at 3 A?

The LD1085DT33R requires a minimum input voltage of 4.9 V to sustain 3.3 V output at 3 A load, based on its guaranteed 1.5 V maximum dropout voltage (V_IN = V_OUT + V_d). Below this, output voltage collapses linearly with input reduction. This value is confirmed in Table 5 of the datasheet under "Electrical characteristics of LD1085#33".

Can LD1085DT33R be used without an output capacitor?

No. A minimum 10 µF output capacitor is mandatory for stability, as specified in the datasheet's "Application schematic" and "Typical characteristics" sections. Omitting it causes oscillation and output voltage overshoot during load transients, verified by Figure 22 (Load transient) and Figure 19 (Stability, V_O = 1.8 V). Ceramic or tantalum types are acceptable.

How does the quiescent current behave under varying load conditions?

Quiescent current remains constant at 5–10 mA across the full 0–3 A load range and is independent of input voltage (up to 30 V), per Table 3–7. Critically, this current flows *into* the load rather than to ground-so total input current equals load current plus I_Q, improving efficiency especially at light loads.

Is LD1085DT33R pin-compatible with older adjustable regulators like LM317?

Yes-LD1085DT33R shares identical pinout (VIN–GND–VOUT) with standard 3-terminal adjustable regulators such as LM317 when used in fixed-output configuration, as stated in the "Pin configuration" section and Figure 2. However, it is not functionally interchangeable with LM317 in adjustable mode due to lack of ADJ pin; it is a fixed-output variant only.