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

STMicroelectronics LD2981ABM33TR

Name: LD2981ABM33TR
Brand: STMicroelectronics
SKU: LD2981ABM33TR
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: LD2981ABM33TR

Manufacturer:: STMicroelectronics

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

Package:: SC-74A, SOT-753

Datasheet:: LD2981ABM33TR.pdf

Description:: IC REG LINEAR 3.3V 100MA SOT23-5

Quantity:: RFQ Add To RFQ list

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Product details

Overview

LD2981ABM33TR from STMicroelectronics is a 100 mA fixed-output ultra-low-dropout linear voltage regulator delivering 3.3 V with ±0.75% output tolerance, 180 mV typical dropout at 100 mA load, and 160 µVRMS output noise. It features logic-controlled inhibit (TTL-compatible), operates from −40 to 125 °C, and is optimized for battery-powered portable electronics requiring low quiescent current and high PSRR.

For engineers reviewing the LD2981ABM33TR datasheet, LD2981ABM33TR pinout, LD2981ABM33TR application, or LD2981ABM33TR equivalent, key selection criteria include shutdown current (<1 µA), dropout performance at light-to-full load, thermal shutdown threshold (170 °C), SOT23-5L package footprint compatibility, and ceramic capacitor stability requirements.

Technical Context

The LD2981ABM33TR uses a PNP pass transistor architecture enabling ultra-low dropout (7 mV typ. at 1 mA) and sub-1 µA off-mode current. Its inhibit input (Pin 3) directly controls internal biasing without pull-up, requiring external logic-level drive between 0 V and ≥1.6 V for ON/OFF states.

Designed for ceramic-capacitor stability, it specifies minimum output capacitance (2.2 µF for 3.3 V versions) and ESR constraints derived from loop-gain analysis across temperature and load. PSRR reaches 63 dB at 1 kHz, and reverse-current protection limits leakage to 160 µA when V_OUT > V_IN.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Voltage	3.3 V ±0.75% (2.925–3.075 V over −40 to 125 °C), enabling precision rail generation for 3.3 V microcontrollers and sensors.
Dropout Voltage	180 mV typ. at 100 mA load, allowing operation with input as low as 3.48 V while maintaining regulation - critical for single-cell Li-ion or coin-cell systems.
Quiescent Current	80 µA typ. at no load (ON mode); <1 µA max in OFF mode, minimizing standby power in always-on IoT nodes.
Noise Voltage	160 µV_RMS (300 Hz–50 kHz), supporting low-noise analog circuits like ADC references and RF front-end biasing.
PSRR	63 dB at 1 kHz, rejecting ripple from switching pre-regulators or noisy DC-DC outputs feeding the LDO input.
Thermal Shutdown	170 °C junction temperature trigger, providing robust overtemperature protection during sustained high-load or poor PCB thermal design.
Inhibit Logic Threshold	V_INH ≤ 0.18 V = OFF; V_INH ≥ 1.6 V = ON, compatible with standard CMOS/TTL GPIO without level-shifting.

Pinout & Package

LD2981ABM33TR is housed in a RoHS-compliant SOT23-5L package (2.9 × 1.6 × 1.3 mm), optimized for space-constrained portable designs and reflow-compatible assembly.

Pin/Terminal	Circuit Role	Design Meaning
1 (VIN)	Input supply connection	Accepts 2.5–16 V DC; requires ≥1 µF ceramic input capacitor placed within 12.7 mm of pin to suppress high-frequency noise and prevent instability.
2 (GND)	Ground reference	Common return path for input/output capacitors and load; must connect to clean analog ground plane to maintain noise performance.
3 (INHIBIT)	Enable/disable control input	TTL-compatible digital input; not internally pulled up - must be driven actively high (≥1.6 V) or low (≤0.18 V); floating state causes undefined operation.
4 (NC)	No-connect terminal	Internally unconnected; must remain unconnected on PCB to avoid parasitic coupling or mechanical stress.
5 (VOUT)	Regulated output	Delivers stable 3.3 V; requires ≥2.2 µF low-ESR ceramic capacitor placed within 12.7 mm of pin to ensure stability across temperature and load transients.

Key Features

Feature	Design Value
Ultra-low dropout	7 mV typ. at 1 mA enables regulation from near-battery-dead voltages (e.g., 3.307 V input sustains 3.3 V output).
Sub-µA shutdown	<1 µA off-mode current extends shelf life and runtime in battery-backed real-time clocks and memory retention circuits.
Ceramic-capacitor optimized	Stable with 2.2 µF/low-ESR X7R ceramics - eliminates need for larger, costlier tantalum or aluminum electrolytics.
High PSRR & low noise	63 dB PSRR at 1 kHz + 160 µV_RMS noise supports sensitive analog signal chains without additional filtering stages.
Reverse-current blocking	No body-diode conduction path; reverse leakage limited to 160 µA when V_OUT > V_IN, preventing backfeed in multi-rail systems.

Applications

Wearable Health Monitor

Industrial Sensor Node

Use Scenario: Compact wearable patch measuring ECG and SpO₂ using ultra-low-power MCU and analog front-end.

IC Role / Device Role / Timing Role: Primary 3.3 V local regulator for MCU core, ADC reference, and BLE radio - enabled/disabled via host MCU GPIO.

Use Value: 80 µA quiescent current and <1 µA shutdown extend coin-cell lifetime beyond 12 months; 160 µV_RMS noise avoids ADC quantization errors.

Use Scenario: Battery-powered wireless vibration sensor deployed in factory machinery with 10-year deployment target.

IC Role / Device Role / Timing Role: Standby-power regulator supplying real-time clock and wake-up controller; inhibited during sleep cycles.

Use Value: Sub-1 µA off-mode current minimizes self-discharge; −40 to 125 °C rating ensures reliability in uncontrolled ambient environments.

Smart Meter RF Module

Automotive Cabin Controller

Use Scenario: Sub-GHz RF transceiver module in AMI smart meters operating from lithium-thionyl-chloride primary cells.

IC Role / Device Role / Timing Role: Low-noise 3.3 V supply for RF synthesizer and baseband IC, dynamically disabled between transmission bursts.

Use Value: 180 mV dropout allows full regulation down to 3.48 V input - maximizing usable cell voltage range before replacement.

Use Scenario: Occupancy-sensing cabin controller in automotive infotainment system with ASIL-B functional safety requirements.

IC Role / Device Role / Timing Role: Secondary 3.3 V rail for proximity sensor interface and CAN transceiver bias, monitored for thermal fault via junction temp sensing.

Use Value: 170 °C thermal shutdown provides fail-safe response under abnormal conditions; AEC-Q100 stress qualification confirmed per ST documentation.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
TPS7A0533PDBVR	Lower IQ (25 µA typ.), but higher dropout (200 mV at 100 mA); no inhibit pin - uses EN only.	Lacks TTL-compatible inhibit; requires external level-shifter for direct GPIO control in legacy designs.	Prefer when lowest possible quiescent current dominates over precise inhibit logic compatibility.
MCP1700T-3302E/MB	Higher dropout (330 mV at 100 mA); 1.8 µA max shutdown current; SOT23-3 package (no INH pin).	Requires external transistor for enable control; lacks dedicated inhibit pin and thermal shutdown flag.	Select when board space is constrained to 3-pin footprint and thermal monitoring is handled externally.

Compared with TPS7A0533PDBVR and MCP1700T-3302E/MB, LD2981ABM33TR uniquely combines TTL-compatible inhibit, 170 °C thermal shutdown, and 160 µV_RMS noise in a 5-pin SOT23 - making it optimal for compact, battery-sensitive designs needing deterministic ON/OFF control and analog integrity.

Availability

LD2981ABM33TR is available at Aetrix Electronics and suitable for wearable health monitors, industrial sensor nodes, smart meter RF modules, and automotive cabin controllers requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for LD2981ABM33TR 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 analog devices for industrial, automotive, and consumer markets.

The LD2981 series belongs to ST's ultra-low-dropout linear regulator product line, engineered specifically for energy-constrained portable and battery-operated systems demanding precision voltage regulation, minimal quiescent power, and robust thermal behavior.

FAQ

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

The LD2981ABM33TR maintains regulation when input voltage exceeds output voltage by its dropout voltage. At 100 mA load, typical dropout is 180 mV, so minimum input is 3.48 V. At 1 mA, dropout drops to 7 mV - allowing regulation from as low as 3.307 V. Full-range specification accounts for worst-case 375 mV dropout at 100 mA and 125 °C.

Can the INHIBIT pin be left unconnected?

No - the INHIBIT pin has no internal pull-up or pull-down. Leaving it floating risks undefined output state and potential oscillation or excessive current draw. If unused, it must be tied directly to VIN to ensure permanent ON operation, per ST's application note section 7.5.

Which output capacitor types and values are validated for stability?

ST validates stability with low-ESR ceramic capacitors: minimum 2.2 µF for 3.3 V versions. X7R dielectric is recommended. Tantalum is possible but not optimized - ceramic offers superior ESR consistency, size, and cost. Capacitor must be placed ≤12.7 mm from VOUT and GND pins with short, low-inductance traces.

Does LD2981ABM33TR support reverse-voltage protection?

It does not provide active reverse-input protection, but its PNP pass transistor structure inherently blocks reverse current from VOUT to VIN. When VOUT exceeds VIN, only 160 µA flows through internal feedback resistors to GND - eliminating need for external blocking diodes in back-fed multi-rail systems.

LD2981ABM33TR Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: SC-74A, SOT-753

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:: Enable

Protection Features:: Over Current, Over Temperature

Operating Temperature:: -40°C ~ 125°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23-5

LD2981ABM33TR FAQ

1.How can I place an order for LD2981ABM33TR through Aetrix?

Please submit a Request for Quotation (RFQ) for LD2981ABM33TR 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 LD2981ABM33TR reliable?

The price and inventory of LD2981ABM33TR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LD2981ABM33TR is usually 5 days.

3.What payment methods are accepted for LD2981ABM33TR?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LD2981ABM33TR transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for LD2981ABM33TR?

LD2981ABM33TR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your LD2981ABM33TR 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 LD2981ABM33TR?

For technical support, including LD2981ABM33TR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LD2981ABM33TR requirements.

6.How does Aetrix verify that LD2981ABM33TR is sourced from the original manufacturer or authorized distributors?

All LD2981ABM33TR 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 LD2981ABM33TR meets industry standards.

7.What is the process for return or replacement of LD2981ABM33TR?

All LD2981ABM33TR units undergo pre-shipment inspection (PSI). If there is an issue with LD2981ABM33TR, 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 LD2981ABM33TR part is unused and in its original packaging.

Return procedure for LD2981ABM33TR:

1.Submit a request within 90 days.

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

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