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

STMicroelectronics LD3985M29R

Name: LD3985M29R
Brand: STMicroelectronics
SKU: LD3985M29R
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: LD3985M29R

Manufacturer:: STMicroelectronics

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

Package:: SC-74A, SOT-753

Datasheet:: LD3985M29R.pdf

Description:: IC REG LINEAR 2.9V 150MA SOT23-5

Quantity:: RFQ Add To RFQ list

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Product details

Overview

LD3985M29R from STMicroelectronics is a 2.9 V fixed-output, 150 mA ultra-low-dropout linear regulator in SOT23-5L package, featuring 60 mV typical dropout at full load, 30 µV_RMS output noise (10 Hz–100 kHz), and logic-controlled shutdown. It operates from 2.5 V to 6 V input, supports low-ESR ceramic capacitors, and targets power-sensitive battery-operated systems such as mobile phone baseband ICs and RF front-end modules.

For engineers reviewing the LD3985M29R datasheet, LD3985M29R pinout, LD3985M29R application, or LD3985M29R equivalent, key selection criteria include dropout voltage under light/heavy load, shutdown quiescent current (<1.5 µA), PSRR performance (60 dB @ 1 kHz), thermal shutdown threshold (160 °C), and compatibility with 1 µF output capacitance.

Technical Context

The LD3985M29R uses BiCMOS process technology to achieve ultra-low quiescent current (85 µA typ. at no load) while maintaining stable regulation across –40 °C to +125 °C junction temperature. Its internal architecture integrates a precision bandgap reference, error amplifier, pass transistor, and thermal/current limiting circuitry - all optimized for low-noise, high-PSRR operation with minimal external components.

Shutdown is controlled via VINH pin with defined logic thresholds (≤0.4 V = OFF, ≥1.2 V = ON); the BYPASS pin accepts a 10 nF capacitor to reduce high-frequency output noise. The regulator maintains >60 dB supply rejection down to input voltages as low as 2.5 V - critical for fading battery rails in portable electronics.

Key Specifications

Parameter	Value and Actual Design Meaning
Output voltage	Fixed 2.9 V ±2% over –40 °C to +125 °C; ensures stable core voltage for 2.8–3.0 V logic domains.
Max output current	150 mA guaranteed; sufficient for powering RF transceivers, sensor interfaces, or MCU peripherals without thermal derating in SOT23-5L.
Dropout voltage	60 mV typ. at 150 mA; enables regulation down to 2.96 V input - extends usable battery life in single-cell Li-ion (3.0–4.2 V) systems.
Output noise	30 µV_RMS (10 Hz–100 kHz); low enough to avoid interference in analog signal chains or PLL reference supplies.
PSRR	60 dB @ 1 kHz, 50 dB @ 10 kHz; suppresses switching noise from DC/DC converters feeding the LDO input.
Quiescent current	85 µA typ. at no load; <1.5 µA in shutdown - minimizes standby leakage in always-on subsystems.
Turn-on time	200 µs typ. (95% of V_O); fast enough for dynamic power sequencing in multi-rail applications.

Pinout & Package

SOT23-5L surface-mount package (1.45 mm × 1.30 mm × 0.95 mm height), RoHS-compliant and ECOPACK® certified, designed for high-density PCB layouts and automated assembly.

Pin/Terminal	Circuit Role	Design Meaning
1 - VI	Input voltage supply	Accepts 2.5–6 V DC; withstands non-repetitive 6.5 V spikes up to 200 ms.
2 - GND	Power ground reference	Common return path for input, output, and internal circuitry; must be low-impedance.
3 - VINH	Logic enable/disable control	Active-high shutdown: ≤0.4 V forces OFF mode (I_Q < 1.5 µA); ≥1.2 V enables regulation.
4 - BYPASS	Noise reduction node	Connects to 10 nF capacitor to shunt high-frequency noise from internal reference and error amp.
5 - VO	Regulated output	Delivers stable 2.9 V ±2%; requires ≥1 µF ceramic output capacitor for stability.

Key Features

Feature	Design Value
Ultra-low dropout	60 mV at 150 mA enables operation with minimal headroom - critical for single-cell Li-ion and coin-cell applications.
Low-noise regulation	30 µV_RMS output noise ensures clean power for RF ICs, ADCs, and clock generators without added filtering.
High PSRR at low V_IN	Maintains >60 dB rejection even at 2.5 V input - preserves noise immunity as battery discharges.
Logic-controlled shutdown	VINH pin allows system-level power gating; <1.5 µA OFF-mode current prevents battery drain during deep sleep.
Stable with ceramic caps	Works with 1–22 µF, 5–5000 mΩ ESR ceramics - eliminates need for bulkier tantalum or electrolytic capacitors.

Applications

Mobile Baseband Power

RF Front-End Biasing

Use Scenario: Powering ARM Cortex-M based modem subsystems in smartphones where input rail varies from 3.2 V to 4.2 V during battery discharge.

IC Role / Device Role / Timing Role: Local LDO providing clean, regulated 2.9 V to baseband processor I/O and memory interface circuits.

Use Value: 60 mV dropout extends functional runtime by ~12 minutes per charge cycle compared to 120 mV-dropout alternatives at end-of-discharge.

Use Scenario: Supplying bias voltage to GaAs pHEMT amplifiers and low-noise RF switches in LTE/Wi-Fi front-end modules.

IC Role / Device Role / Timing Role: Low-noise post-regulator cleaning switched-mode supply ripple before RF signal path stages.

Use Value: 30 µV_RMS noise and 60 dB PSRR prevent AM-to-PM distortion and phase noise degradation in transmit chains.

Wearable Sensor Hub

IoT Edge Node MCU Core

Use Scenario: Powering MEMS accelerometer, gyroscope, and environmental sensor clusters in compact wearables with tight thermal constraints.

IC Role / Device Role / Timing Role: Primary voltage regulator delivering 2.9 V to mixed-signal sensor interface ASICs and digital controllers.

Use Value: 85 µA quiescent current and 1.5 µA shutdown current reduce average system power by 18 µW - extending battery life by 3.2 weeks in 7-day monitoring mode.

Use Scenario: Providing core voltage to ultra-low-power microcontrollers (e.g., STM32L4+) in battery-powered industrial IoT nodes.

IC Role / Device Role / Timing Role: Always-on LDO supporting real-time clock, wake-up comparator, and retention RAM during deep-sleep states.

Use Value: Guaranteed 150 mA output and thermal shutdown (160 °C) allow safe burst-mode operation during wireless transmission without external thermal management.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
Torex XC6206P292MR	2.9 V fixed, 150 mA, 120 mV dropout at 150 mA; 25 µV_RMS noise; no shutdown pin.	Lacks logic-controlled shutdown - requires external MOSFET for system-level power gating.	Select when shutdown functionality is unnecessary and lower cost is prioritized over dropout performance.
Richtek RT9013-29GB	2.9 V fixed, 300 mA, 250 mV dropout at 300 mA; 45 µV_RMS noise; 0.5 µA shutdown current.	Higher current capability but larger dropout and noise - less suitable for noise-critical RF biasing.	Prefer when higher output current is required and board space allows SO-8 or SOT23-5 footprint adaptation.

Compared with XC6206P292MR and RT9013-29GB, the LD3985M29R uniquely balances ultra-low dropout (60 mV), sub-30 µV noise, and integrated shutdown in SOT23-5L - making it optimal for space-constrained, battery-sensitive RF and portable computing applications where every millivolt and microamp matters.

Availability

LD3985M29R is available at Aetrix Electronics and suitable for mobile communications, wearable health monitors, and industrial IoT edge nodes requiring stable component supply, long-lifecycle support, and consistent parametric performance across temperature and load conditions.

Supply support for LD3985M29R 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 automotive, industrial, and consumer markets.

The LD3985 series belongs to ST's ultra-low-noise, low-quiescent-current LDO portfolio, engineered specifically for battery-powered portable electronics demanding extended runtime, clean power, and small-footprint integration.

FAQ

What is the minimum output capacitor required for stable operation of LD3985M29R?

The LD3985M29R requires a minimum 1 µF ceramic output capacitor with ESR between 5 mΩ and 5000 mΩ. Stability is maintained across temperature and tolerance variations, including ±30% capacitor tolerance. X5R or X7R dielectrics are recommended; no additional ESR stabilization network is needed.

Can LD3985M29R operate with an input voltage below 2.5 V?

No. The absolute minimum operating input voltage is 2.5 V per datasheet specifications. Operation below this level is not guaranteed and may result in loss of regulation, increased dropout, or undefined behavior. The device is not characterized for sub-2.5 V operation.

How does the BYPASS pin affect output noise performance?

The BYPASS pin connects to a 10 nF capacitor that filters high-frequency noise from the internal reference and error amplifier. This reduces output noise by ~15–20% in the 100 kHz–1 MHz range and improves PSRR above 100 kHz. Leaving it unconnected increases broadband noise by up to 2×.

Is thermal shutdown automatically reset after cooling?

Yes. Thermal shutdown activates at 160 °C junction temperature and includes ~20 °C hysteresis. Once the die cools below ~140 °C, regulation resumes automatically without requiring a cycle of the VINH pin or input power - enabling self-recovery in transient overload conditions.

LD3985M29R 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):: 6V

Voltage - Output (Min/Fixed):: 2.9V

Voltage - Output (Max):: -

Voltage Dropout (Max):: 0.1V @ 150mA

Current - Output:: 150mA

Current - Quiescent (Iq):: 150 µA

Current - Supply (Max):: 250 µA

PSRR:: 60dB ~ 50dB (1kHz ~ 10kHz)

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

LD3985M29R FAQ

1.How can I place an order for LD3985M29R through Aetrix?

Please submit a Request for Quotation (RFQ) for LD3985M29R 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 LD3985M29R reliable?

The price and inventory of LD3985M29R are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LD3985M29R is usually 5 days.

3.What payment methods are accepted for LD3985M29R?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LD3985M29R transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for LD3985M29R?

LD3985M29R orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your LD3985M29R 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 LD3985M29R?

For technical support, including LD3985M29R datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LD3985M29R requirements.

6.How does Aetrix verify that LD3985M29R is sourced from the original manufacturer or authorized distributors?

All LD3985M29R 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 LD3985M29R meets industry standards.

7.What is the process for return or replacement of LD3985M29R?

All LD3985M29R units undergo pre-shipment inspection (PSI). If there is an issue with LD3985M29R, 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 LD3985M29R part is unused and in its original packaging.

Return procedure for LD3985M29R:

1.Submit a request within 90 days.

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

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