STMicroelectronics LD1084D2M33R

Overview

LD1084D2M33R from STMicroelectronics is a 5 A low-dropout positive adjustable voltage regulator in TO-220 package, featuring ±1% output voltage tolerance at 25 °C, 1.3 V typical dropout at 5 A, and internal thermal/overcurrent protection. It delivers stable regulated output for industrial power rails requiring high current and tight regulation, such as 3.3 V logic supply in programmable logic controllers.

For engineers reviewing the LD1084D2M33R datasheet, LD1084D2M33R pinout, LD1084D2M33R application, or LD1084D2M33R equivalent, key selection criteria include dropout voltage at full load, adjust pin current stability across temperature, line/load regulation performance, and thermal resistance (R_thJC = 3 °C/W) for heatsink design validation.

Technical Context

The LD1084D2M33R uses an NPN-based pass transistor architecture, enabling quiescent current to flow into the load rather than being wasted-improving efficiency over PNP regulators. Its reference voltage is trimmed on-chip to 1.25 V (±1% at 25 °C), supporting precise external resistor-set outputs via the ADJ pin.

It operates across –40 °C to +125 °C junction temperature with internally limited power dissipation and short-circuit current that varies with dropout (e.g., 6.5 A at VI–VO = 5 V). Stability requires ≥10 µF output capacitance; optional CADJ improves ripple rejection.

Key Specifications

Pinout & Package

Supplied in TO-220 package with exposed metal tab (electrically connected to Pin 2), offering mechanical robustness and direct heatsinking capability. Pin 1 (Input), Pin 2 (Output), Pin 3 (Adjust) configured in standard three-terminal layout.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM338K and LT1084-CT, the LD1084D2M33R offers superior thermal performance (R_thJC = 3 °C/W), lower dropout, and tighter initial tolerance-making it optimal for space-constrained industrial 5 A applications where input headroom and heatsink size are critical.

Availability

LD1084D2M33R is available at Aetrix Electronics and suitable for industrial automation, test instrumentation, and telecom infrastructure requiring stable component supply, long-lifecycle support, and guaranteed TO-220 packaging consistency.

Supply support for LD1084D2M33R 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, sensors, and discrete components for industrial, automotive, and consumer markets.

The LD1084 belongs to ST's high-current linear regulator product line, engineered specifically for industrial power systems demanding reliability, thermal resilience, and precision regulation under variable load and temperature conditions.

FAQ

What is the minimum load current required for stable operation of LD1084D2M33R?

The LD1084D2M33R requires a minimum load current of 3 mA at VI = 30 V, per Table 4 in the datasheet. This ensures proper biasing of internal circuitry and prevents output voltage overshoot during light-load transients. For 3.3 V output configurations, a 1 kΩ pull-down resistor on the output satisfies this requirement while adding negligible power loss.

Can LD1084D2M33R be used without an output capacitor?

No. A minimum 10 µF output capacitor is mandatory for stability, as confirmed in Section 4 (Schematic application) and Figure 24/26 (stability plots). Omitting it causes oscillation and potential device failure. Tantalum or low-ESR ceramic capacitors are acceptable; aluminum electrolytics require ≥22 µF due to higher ESR.

How does the adjust pin current affect output voltage accuracy?

The ADJ pin draws 55–120 µA, which flows through the lower resistor (R2) in the feedback divider. This introduces a systematic error: VO = VREF × (1 + R1/R2) + I_ADJ × R2. For a 3.3 V design with R2 = 1.2 kΩ, this adds ~0.12 V offset-requiring R2 reduction or use of a 3-terminal fixed variant like LD1084V33.

Is the TO-220 tab electrically connected, and how should it be mounted?

Yes-the metal tab is internally connected to Pin 2 (OUT), as shown in Figure 2 (pin connections) and confirmed in the TO-220 mechanical drawings. When mounting to a grounded heatsink, electrical isolation (e.g., mica washer + nylon screw) is mandatory to avoid shorting the output to ground. Thermal paste must be applied between tab and heatsink surface for optimal R_thJC performance.