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

STMicroelectronics LD2981CU33TR

Name: LD2981CU33TR
Brand: STMicroelectronics
SKU: LD2981CU33TR
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: LD2981CU33TR

Manufacturer:: STMicroelectronics

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

Package:: TO-243AA

Datasheet:: LD2981CU33TR.pdf

Description:: IC REG LINEAR 3.3V 100MA SOT89-3

Quantity:: RFQ Add To RFQ list

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Inventory:4,356

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Product details

Overview

LD2981CU33TR from STMicroelectronics is a 100 mA fixed-output ultra-low-dropout linear voltage regulator with logic-controlled inhibit function, delivering 3.3 V ±0.75% over −40 to 125 °C, featuring 160 µV_RMS output noise and 7 mV typical dropout at 1 mA load. It serves as a local power rail regulator in portable battery-powered systems requiring low quiescent current and fast transient response.

For engineers reviewing the LD2981CU33TR datasheet, LD2981CU33TR pinout, LD2981CU33TR application, or LD2981CU33TR equivalent, key selection criteria include shutdown current (<1 µA), dropout voltage at light/heavy load, output voltage tolerance across temperature, and compatibility with low-ESR ceramic capacitors in SOT23-5L packaging.

Technical Context

The LD2981CU33TR employs a PNP pass transistor architecture enabling ultra-low dropout (180–250 mV at 100 mA) and sub-1 µA off-mode quiescent current. Its inhibit input (Pin 3) accepts TTL-compatible logic levels (V_IL ≤ 0.18 V, V_IH ≥ 1.6 V) to enable/disable regulation without external pull-up.

Designed for stability with 2.2 µF ceramic output capacitance, it achieves 160 µV_RMS noise (300 Hz–50 kHz) and 63 dB supply voltage rejection at 1 kHz. Internal thermal shutdown (170 °C) and current limiting protect against fault conditions.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Voltage	3.3 V ±0.75% (−40 to 125 °C), ensuring stable MCU core or RF bias rail under thermal stress
Dropout Voltage	180–250 mV at 100 mA load, enabling operation from single-cell Li-ion (3.0 V min) or 3.3 V backplane
Quiescent Current	80 µA typ. (no load, on mode); <1 µA (off mode), critical for battery runtime in standby
Noise Voltage	160 µV_RMS (300 Hz–50 kHz), suitable for noise-sensitive analog/RF circuitry without added filtering
Supply Rejection	63 dB at 1 kHz, suppressing switching noise from upstream DC/DC converters
Operating Temp	−40 to 125 °C junction, supporting automotive cabin and industrial control environments
Max Output Current	100 mA continuous, sufficient for microcontrollers, sensors, and low-power peripherals

Pinout & Package

LD2981CU33TR is housed in a RoHS-compliant SOT23-5L package (1.3 mm × 2.9 mm × 1.1 mm), optimized for space-constrained PCB layouts and reflow assembly.

Pin/Terminal	Circuit Role	Design Meaning
1 (VIN)	Input supply connection	Accepts 2.5–16 V DC; requires 1 µF ceramic capacitor within 12.7 mm of pin for stability
2 (GND)	Analog ground reference	Must connect to clean analog ground plane; separates feedback and power return paths
3 (INHIBIT)	Logic-controlled shutdown input	TTL-compatible; pulls low (<0.18 V) to disable output and reduce I_Q to <1 µA; not internally pulled up
4 (NC)	No-connect terminal	Internally unconnected; must remain floating-no external connection permitted
5 (VOUT)	Regulated 3.3 V output	Delivers up to 100 mA; requires 2.2 µF low-ESR ceramic capacitor placed adjacent to pin

Key Features

Feature	Design Value
Ultra-low dropout	7 mV typ. at 1 mA enables regulation from near-output voltages (e.g., 3.31 V input → 3.3 V out)
Logic inhibit control	Direct TTL-level ON/OFF control eliminates need for external MOSFET switch or level shifter
Low-noise output	160 µV_RMS noise avoids post-regulation filtering in audio, sensor, or RF signal chains
Thermal protection	170 °C junction shutdown prevents damage during sustained overload or poor heatsinking
Ceramic capacitor compatible	Stable with 2.2 µF X5R/X7R ceramics-no tantalum required, reducing BOM cost and size

Applications

Cellular Handset Power Management

Industrial Sensor Node

Use Scenario: Regulating 3.3 V rail for baseband processor, PMIC, and RF transceiver in GSM/UMTS handsets.

IC Role / Device Role / Timing Role: Local LDO providing clean, low-noise supply with dynamic load transient response <10 µs.

Use Value: Enables 100 mA peak current delivery during TX bursts while maintaining <1% output deviation and <1 µA shutdown current between transmissions.

Use Scenario: Powering ultra-low-power microcontroller, MEMS accelerometer, and BLE radio in battery-operated condition monitoring nodes.

IC Role / Device Role / Timing Role: Primary system regulator with logic-controlled sleep mode synchronized to sensor sampling intervals.

Use Value: Extends 2×AA battery life to >5 years by reducing quiescent current to <1 µA during 99.9% idle time while retaining fast wake-up capability.

Medical Wearable Monitor

Automotive Body Control Module

Use Scenario: Supplying ECG front-end analog circuitry and low-power MCU in compact wearable heart rate monitors.

IC Role / Device Role / Timing Role: Noise-critical analog rail regulator with tight output tolerance and high PSRR.

Use Value: Meets IEC 60601-1 EMI requirements without additional ferrite beads or LC filters due to 160 µV_RMS noise and 63 dB SVR.

Use Scenario: Providing 3.3 V logic supply for LIN transceivers and door module MCUs in harsh automotive environments.

IC Role / Device Role / Timing Role: High-reliability local regulator with extended temperature range and thermal shutdown.

Use Value: Ensures uninterrupted operation at 125 °C ambient and survives load dump transients via internal current and thermal limiting.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
AP2112K-3.3TRG1	Higher quiescent current (65 µA typ. on, 1 µA off); 300 mV dropout at 100 mA; no inhibit pin	Lacks logic shutdown-requires external FET for system-level power gating	Select when inhibit function is unnecessary and board space permits larger dropout margin
MCP1700T-3302E/TT	Lower max current (250 mA); 175 mV dropout at 250 mA; 1.6 µA quiescent (off); SOT23-3 package	Single-inhibit-pin omission simplifies layout but removes independent rail control	Prefer for higher-current, lower-cost designs where per-rail shutdown is not required

Compared with AP2112K-3.3TRG1 and MCP1700T-3302E/TT, LD2981CU33TR uniquely combines sub-1 µA shutdown, 180 mV dropout at full load, and dedicated inhibit control in SOT23-5L-enabling precise, low-power domain management in multi-rail portable systems.

Availability

LD2981CU33TR is available at Aetrix Electronics and suitable for cellular handset power management, industrial sensor node design, and medical wearable monitor development requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD2981CU33TR 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 analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The LD2981 belongs to ST's ultra-low-dropout LDO family, engineered specifically for battery-powered portable electronics demanding minimal quiescent current, high accuracy, and robust transient performance in miniature packages.

FAQ

What is the minimum input voltage required for regulation at 3.3 V output?

The LD2981CU33TR maintains regulation with input as low as 3.48 V at 100 mA load (3.3 V + 180 mV dropout). At lighter loads, dropout drops to 7 mV-so 3.307 V input suffices at 1 mA. Input must remain ≥2.5 V per absolute maximum ratings, but functional regulation requires VIN ≥ VO + VDROP across all operating conditions.

Can the INHIBIT pin be left unconnected?

No-the INHIBIT pin is not internally pulled up or down and must never be left floating. Leaving it unconnected risks undefined output state and potential oscillation. If shutdown control is unused, tie Pin 3 directly to VIN to ensure permanent ON operation, as specified in ST's application notes.

Which output capacitor types and values ensure stability?

ST specifies 2.2 µF X5R/X7R ceramic capacitors with ESR ≤ 100 mΩ for 3.3 V versions. Tantalum capacitors may work but are discouraged due to higher ESR, cost, and size. Capacitor must be placed ≤12.7 mm from VOUT and GND pins; lower values require series resistance per Figures 18–19 in the datasheet to maintain phase margin.

Does LD2981CU33TR support reverse current protection?

Yes-the internal PNP pass transistor lacks a body diode, preventing reverse current flow from VOUT to VIN. When VOUT exceeds VIN, only ~160 µA flows through internal feedback resistors to GND (per Figure 22), eliminating need for external blocking diodes in backup-supply or hot-swap configurations.

LD2981CU33TR Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-243AA

Packaging:: Tape & Reel (TR)

Product Status:: Active

Output Configuration:: Positive

Output Type:: Fixed

Number of Regulators:: 1

Voltage - Input (Max):: 16V

Voltage - Output (Min/Fixed):: 3.3V

Voltage - Output (Max):: -

Voltage Dropout (Max):: 0.375V @ 100mA

Current - Output:: 100mA

Current - Quiescent (Iq):: 150 µA

Current - Supply (Max):: 2.6 mA

PSRR:: 63dB (1kHz)

Control Features:: -

Protection Features:: Over Current, Over Temperature

Operating Temperature:: -40°C ~ 125°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-89-3

LD2981CU33TR FAQ

1.How can I place an order for LD2981CU33TR through Aetrix?

Please submit a Request for Quotation (RFQ) for LD2981CU33TR 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 LD2981CU33TR reliable?

The price and inventory of LD2981CU33TR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LD2981CU33TR is usually 5 days.

3.What payment methods are accepted for LD2981CU33TR?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LD2981CU33TR transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for LD2981CU33TR?

LD2981CU33TR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your LD2981CU33TR 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 LD2981CU33TR?

For technical support, including LD2981CU33TR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LD2981CU33TR requirements.

6.How does Aetrix verify that LD2981CU33TR is sourced from the original manufacturer or authorized distributors?

All LD2981CU33TR 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 LD2981CU33TR meets industry standards.

7.What is the process for return or replacement of LD2981CU33TR?

All LD2981CU33TR units undergo pre-shipment inspection (PSI). If there is an issue with LD2981CU33TR, 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 LD2981CU33TR part is unused and in its original packaging.

Return procedure for LD2981CU33TR:

1.Submit a request within 90 days.

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

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