STMicroelectronics LD1085V33

Overview

LD1085V33 from STMicroelectronics is a fixed-output 3.3 V, 3 A low-dropout linear voltage regulator in TO-220 package. It delivers ±1% output voltage tolerance at 25 °C, guarantees 1.3 V typical dropout at full load, supports -40 °C to +125 °C junction temperature, and requires only a 10 µF output capacitor for stability. It serves as a primary power rail regulator in industrial control modules where precise, high-current 3.3 V supply is required.

For engineers reviewing the LD1085V33 datasheet, LD1085V33 pinout, LD1085V33 application, or LD1085V33 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 LD1085V33 integrates an internal bandgap reference (1.25 V), error amplifier, and NPN pass transistor - enabling low quiescent current (5–10 mA) that flows into the load rather than being wasted. Its dropout voltage remains stable across temperature (−40 °C to +125 °C) and load (0–3 A), with thermal regulation of 0.008–0.04 %/W ensuring minimal output drift during transient heating.

It features internal power and thermal limiting, short-circuit protection with current foldback (3.2–4.5 A at 5 V dropout), and supply voltage rejection of 60–72 dB at 120 Hz. The device operates with input voltages from 4.9 V to 30 V and maintains ±2% output tolerance over full temperature and load range.

Key Specifications

Pinout & Package

LD1085V33 is supplied in TO-220 package (ECOPACK® compliant), featuring integrated heatsink tab (pin 2) for direct mounting to PCB copper pour or external heatsink. Thermal resistance junction-to-case is 3 °C/W, enabling >2.5 W power dissipation with modest heatsinking.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM350T and TLV1117-33, LD1085V33 uniquely combines 3 A current, 1.3 V dropout, ±1% tolerance, and industrial temperature support in a single TO-220 package - making it the only option among the three suitable for high-reliability, high-current 3.3 V rail generation without external components or thermal compromises.

Availability

LD1085V33 is available at Aetrix Electronics and suitable for industrial automation controllers, embedded networking hardware, and medical sensor subsystems requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for LD1085V33 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.

LD1085V33 belongs to ST's high-current linear regulator product line, engineered specifically for industrial and embedded systems needing robust, fixed-output voltage regulation with minimal external components and guaranteed thermal safety.

FAQ

What is the minimum input voltage required for LD1085V33 to regulate 3.3 V at 3 A?

The minimum input voltage is 4.9 V - derived from the 3.3 V output plus 1.3 V typical dropout voltage at full load. Operation below 4.9 V results in dropout mode, where output voltage drops linearly with input. Input must remain ≥4.9 V under worst-case conditions including line tolerance, temperature drift, and load transients.

Can LD1085V33 be used with ceramic output capacitors?

Yes - the LD1085V33 is stable with ceramic capacitors ≥10 µF and ESR ≥5 mΩ. Unlike older LDOs, it does not require high-ESR tantalum or aluminum electrolytic capacitors. Use X5R/X7R dielectrics rated for ≥6.3 V; avoid COG/NP0 types below 10 µF due to insufficient capacitance at bias.

How does the LD1085V33 handle short-circuit conditions?

It employs foldback current limiting: short-circuit current is 3.2–4.5 A when VIN–VOUT = 5 V, but decreases to 0.2–0.5 A at 25 V differential. Combined with thermal shutdown, this prevents destructive power dissipation. Recovery is automatic after fault removal and junction cooling below thermal trip threshold.

Is the TO-220 tab electrically isolated in LD1085V33?

No - the metal tab is internally connected to Pin 2 (GND). This is confirmed in ST's mechanical drawings and thermal data tables (R_thJC defined between junction and tab). When mounting to heatsinks, electrical isolation (e.g., mica washer + shoulder washer) is mandatory unless the heatsink is grounded.