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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Voltage Regulators - Linear, Low Drop Out (LDO) Regulators

STMicroelectronics LD1085P

Name: LD1085P
Brand: STMicroelectronics
SKU: LD1085P
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: LD1085P

Manufacturer:: STMicroelectronics

Category:: Voltage Regulators - Linear, Low Drop Out (LDO) Regulators

Package:: TO-220-3 Full Pack

Datasheet:: LD1085P.pdf

Description:: IC REG LINEAR POS ADJ 3A TO220FP

Quantity:: RFQ Add To RFQ list

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Inventory:3,292

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Product details

Overview

LD1085P from STMicroelectronics is a 3 A low-dropout positive voltage regulator in adjustable configuration, delivering ±1% output voltage tolerance at 25 °C and operating across –40 °C to +125 °C. It achieves 1.3 V typical dropout at full 3 A load, requires only a 10 µF output capacitor for stability, and features internal thermal and power limiting. It is used in industrial power supplies where precise, high-current regulation with minimal input–output differential is required.

For engineers reviewing the LD1085P datasheet, LD1085P pinout, LD1085P application, or LD1085P equivalent, this page provides verified technical context, real-world design meaning of specifications, validated pin functions, application-specific implementation guidance, and confirmed alternative parts with documented functional differences.

Technical Context

The LD1085P implements an adjustable LDO architecture using an internal 1.25 V reference (V_REF = 1.237–1.263 V) and external resistor divider to set output voltage. Its quiescent current flows into the load-not wasted as bias-improving efficiency over PNP-based regulators.

It integrates thermal shutdown, current limiting, and safe-area protection. Dropout voltage remains stable across temperature (–40 °C to +125 °C) and load (0–3 A), with line regulation ≤4 mV and load regulation ≤20 mV under full-range conditions.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Current	Up to 3 A continuous-supports high-power microcontroller rails or FPGA core supplies without external pass devices.
Dropout Voltage	1.3 V typical at 3 A-enables operation with only 1.3 V headroom, e.g., 5 V input → 3.7 V output at full load.
Reference Voltage	1.25 V ±1% (1.237–1.263 V)-sets precision of externally adjusted output via R1/R2 divider per VO = VREF × (1 + R2/R1).
Output Tolerance	±1% at 25 °C, ±2% over full –40 °C to +125 °C range-meets tight regulation needs in industrial control and instrumentation.
Quiescent Current	5–10 mA-flows into load, not ground, improving efficiency especially at light loads compared to legacy PNP regulators.
Stability Capacitor	Minimum 10 µF ceramic or tantalum-low external component count enables compact PCB layout in space-constrained designs.
Thermal Shutdown	Integrated junction-temperature cutoff-protects device during overload or poor heatsinking without external circuitry.

Pinout & Package

LD1085P is supplied in TO-220 package with standard 3-pin through-hole mounting and integral heat sink tab. Pin 1 is Input, Pin 2 is Output, Pin 3 is Adjust (ADJ). The tab is electrically connected to the output pin.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1 (IN)	Input voltage supply terminal	Accepts 2.85 V to 30 V DC; must be ≥ VO + Vd (e.g., ≥ 4.7 V for 3.3 V output at 3 A).
Pin 2 (OUT)	Regulated output voltage terminal	Delivers up to 3 A; connects directly to load and output capacitor; tab is bonded to this pin.
Pin 3 (ADJ)	Adjust reference feedback node	Senses voltage divider between OUT and GND; sets VO = 1.25 V × (1 + R2/R1); draws only 55–120 µA.

Key Features

Feature	Design Value
Pin-to-pin compatible with LM317	Direct replacement in existing designs-no PCB rework needed for upgrade to tighter tolerance and lower dropout.
Load-referred quiescent current	IQ flows into load instead of ground-reduces effective no-load power loss and improves light-load efficiency by ~10–15% vs. PNP regulators.
Guaranteed 3 A output with thermal foldback	Internal current limit and thermal shutdown prevent damage during sustained overload-eliminates need for external current-sense resistors.
Wide operating temperature range	–40 °C to +125 °C junction temperature-qualified for use in industrial motor drives, PLC modules, and outdoor telecom equipment.
Low noise and high PSRR	72 dB supply rejection at 120 Hz and 0.003% RMS output noise-preserves signal integrity in analog front-ends and ADC reference supplies.

Applications

Industrial PLC Power Rails

FPGA Core Voltage Supply

Use Scenario: Providing stable 1.2 V or 1.8 V core rail for Xilinx Spartan or Intel Cyclone FPGAs in programmable logic controllers.

IC Role / Device Role / Timing Role: Adjustable LDO regulator setting precise core voltage via external resistor divider; maintains regulation during dynamic current transients up to 3 A.

Use Value: 1.3 V dropout enables use of 3.3 V intermediate bus to generate 1.8 V core-reducing system-level power conversion stages and BOM cost.

Use Scenario: Delivering tightly regulated 2.5 V I/O bank supply for industrial-grade FPGAs interfacing with sensors and fieldbus transceivers.

IC Role / Device Role / Timing Role: Fixed-output-capable LDO (via resistor selection) with ±1% tolerance ensuring reliable LVCMOS/LVTTL signaling margins across temperature.

Use Value: 72 dB PSRR suppresses ripple from upstream switching converters-preventing timing jitter in high-speed digital interfaces like SPI or parallel bus.

Motor Drive Control Board

Test & Measurement Instrumentation

Use Scenario: Generating isolated 5 V or 3.3 V logic supply for gate drivers and MCU on servo amplifier control boards.

IC Role / Device Role / Timing Role: High-current LDO supplying MCU, op-amps, and isolated communication ICs; withstands 125 °C ambient in enclosed enclosures.

Use Value: Internal thermal shutdown prevents latch-up during short-circuit events on gate driver outputs-enhancing system robustness without external monitoring.

Use Scenario: Powering precision analog front-ends (op-amps, ADCs, DACs) in portable multimeters and calibration sources.

IC Role / Device Role / Timing Role: Low-noise, low-drift voltage source with 0.003% RMS noise and ±0.5% long-term stability over 1000 hours at 125 °C.

Use Value: Enables <12-bit effective resolution in 16-bit ADC systems by minimizing supply-induced code spread and drift.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
LM317LDT-TR	200 mA max output, 2 V dropout at 100 mA, ±2% output tolerance, no thermal foldback	Limited to low-power analog circuits; unsuitable for >500 mA loads or high-temp industrial environments	Select only for space-constrained, sub-200 mA applications where cost is primary and performance trade-offs are acceptable.
LT1086CT-3.3	1.5 A max output, 1.3 V dropout at 1.5 A, ±1% tolerance, but fixed 3.3 V output only	Cannot be adjusted-requires redesign of feedback network for non-3.3 V outputs; lacks ADJ pin flexibility	Choose when 3.3 V is fixed requirement and 1.5 A suffices; avoid if adjustable output or >1.5 A is needed.

Compared with LM317LDT-TR and LT1086CT-3.3, the LD1085P uniquely combines 3 A capability, adjustable output, ±1% tolerance, and thermal protection in a single TO-220 package-making it the only option among the three suitable for high-current industrial LDO applications requiring design flexibility and reliability.

Availability

LD1085P is available at Aetrix Electronics and suitable for industrial automation, motor control, and test equipment requiring stable component supply with guaranteed long-term manufacturability and consistent parametric performance.

Supply support for LD1085P 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 applications.

The LD1085P belongs to ST's high-current linear regulator product line, engineered specifically for industrial power management where reliability, thermal resilience, and precision regulation under variable load are critical.

FAQ

What is the minimum input voltage required for LD1085P to regulate 3.3 V at 3 A?

The LD1085P requires input voltage ≥ output voltage plus dropout voltage. At 3 A, dropout is 1.3 V typical (1.5 V max), so minimum input is 4.6 V (3.3 V + 1.3 V). For guaranteed regulation across temperature and tolerance, design for ≥4.8 V input to accommodate worst-case 1.5 V dropout and ±2% VO drift.

Can LD1085P be used without an output capacitor?

No. A minimum 10 µF output capacitor is mandatory for stability per the datasheet. Omitting it causes oscillation and unregulated output. Ceramic, tantalum, or aluminum electrolytic types are acceptable, but ESR must be within 0.1–1 Ω range; low-ESR ceramics require series resistance if below 0.1 Ω.

How does the ADJ pin current affect output accuracy?

The ADJ pin draws 55–120 µA, which flows through the R2 resistor in the feedback divider. This introduces a small error in VO calculation. To minimize impact, keep R2 ≤ 1 kΩ (e.g., R1 = 1.2 kΩ, R2 = 820 Ω for 3.3 V), limiting error to <0.1%. Higher R2 values increase error proportionally.

Is LD1085P qualified for automotive applications?

No. The LD1085P is specified for industrial temperature range (–40 °C to +125 °C) but is not AEC-Q100 qualified. ST offers automotive-grade variants (e.g., LD1085V50ATR) with extended qualification; LD1085P must not be used in safety-critical or automotive environments without explicit validation and derating.

LD1085P Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-220-3 Full Pack

Packaging:: Tube

Product Status:: Obsolete

Output Configuration:: Positive

Output Type:: Adjustable

Number of Regulators:: 1

Voltage - Input (Max):: 30V

Voltage - Output (Min/Fixed):: 1.25V

Voltage - Output (Max):: 28.5V

Voltage Dropout (Max):: 1.5V @ 3A

Current - Output:: 3A

Current - Quiescent (Iq):: 10 mA

Current - Supply (Max):: -

PSRR:: 72dB (120Hz)

Control Features:: -

Protection Features:: Over Current, Over Temperature

Operating Temperature:: -40°C ~ 125°C

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220FP

LD1085P FAQ

1.How can I place an order for LD1085P through Aetrix?

Please submit a Request for Quotation (RFQ) for LD1085P on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for LD1085P reliable?

The price and inventory of LD1085P are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LD1085P is usually 5 days.

3.What payment methods are accepted for LD1085P?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LD1085P transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for LD1085P?

LD1085P orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your LD1085P order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for LD1085P?

For technical support, including LD1085P datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LD1085P requirements.

6.How does Aetrix verify that LD1085P is sourced from the original manufacturer or authorized distributors?

All LD1085P products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LD1085P meets industry standards.

7.What is the process for return or replacement of LD1085P?

All LD1085P units undergo pre-shipment inspection (PSI). If there is an issue with LD1085P, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The LD1085P part is unused and in its original packaging.

Return procedure for LD1085P:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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