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

STMicroelectronics LDS3985M18R

Name: LDS3985M18R
Brand: STMicroelectronics
SKU: LDS3985M18R
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: LDS3985M18R

Manufacturer:: STMicroelectronics

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

Package:: SC-74A, SOT-753

Datasheet:: LDS3985M18R.pdf

Description:: IC REG LINEAR 1.8V 300MA SOT23-5

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Product details

Overview

LDS3985M18R from STMicroelectronics is a fixed 1.8 V, 300 mA low-dropout (LDO) linear voltage regulator in SOT23-5L package, featuring 150 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 and delivers ultra-low quiescent current (85 µA typ. at no load), making it suitable for battery-powered mobile phones and portable information appliances.

For engineers reviewing the LDS3985M18R datasheet, LDS3985M18R pinout, LDS3985M18R application, or LDS3985M18R equivalent, key selection criteria include guaranteed 300 mA output with <250 mV max dropout across temperature, automotive-grade thermal shutdown at 160 °C, SVR of 55 dB at 1 kHz, and compatibility with low-ESR ceramic capacitors down to 2.2 µF.

Technical Context

The LDS3985M18R employs BiCMOS process technology to achieve ultra-low dropout and quiescent current simultaneously. Its internal architecture integrates a precision bandgap reference, error amplifier, PMOS pass transistor, and independent bypass capacitor node for noise filtering.

Logic-controlled inhibit (VINH) enables precise system-level power sequencing: device enters OFF mode when VINH ≤ 0.4 V (max 1.5 µA shutdown current), and turns on within 240 µs (typ.) when VINH ≥ 1.4 V. Thermal protection activates at 160 °C with ~20 °C hysteresis.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Voltage	Fixed 1.8 V ±2% over -40 °C to 125 °C; ensures stable core supply for 1.8 V logic rails.
Max Output Current	300 mA guaranteed; supports moderate-power microcontrollers and RF front-ends without thermal derating in SOT23-5L.
Dropout Voltage	150 mV typ. at 300 mA; enables operation with only 1.95 V input, critical for single-cell Li-ion or Li-poly systems.
Output Noise	30 µV_RMS (10 Hz–100 kHz); minimizes jitter in analog/RF sections powered from this LDO.
Supply Rejection	55 dB at 1 kHz; suppresses switching noise from upstream DC-DC converters feeding the LDO input.
Quiescent Current	85 µA typ. at no load; extends battery life in always-on sensor nodes and standby modes.
Shutdown Current	1.5 µA max at -40 °C to 125 °C; enables deep-sleep power gating in portable devices.

Pinout & Package

SOT23-5L package: 5-pin surface-mount, 2.95 mm × 1.60 mm footprint, 1.45 mm height, ECOPACK® compliant. Thermal resistance R_thJA = 255 °C/W.

Pin/Terminal	Circuit Role	Design Meaning
1 (VI)	LDO input voltage	Accepts 2.5–6 V DC input; withstands non-repetitive 6.5 V spikes up to 200 ms.
2 (GND)	Common ground	Reference node for all internal circuitry and external capacitors; must be low-impedance.
3 (VINH)	Inhibit control input	Active-high enable: ≥1.4 V = ON, ≤0.4 V = OFF; requires external pull-up/down-no internal bias.
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 1.8 V to load; requires 2.2 µF ceramic output capacitor (5–5000 mΩ ESR).

Key Features

Feature	Design Value
Ultra-low dropout	150 mV typ. at 300 mA enables use with weak or deeply discharged batteries.
Low-noise regulation	30 µV_RMS output noise supports noise-sensitive analog circuits without additional filtering.
Logic-controlled shutdown	VINH pin allows precise system-level power sequencing and zero-load current during sleep.
Stable with ceramic caps	Validated for 2.2–22 µF ceramic output capacitors (5–5000 mΩ ESR), reducing BOM cost and size.
Wide temperature range	-40 °C to +125 °C operation supports industrial and under-hood automotive environments.

Applications

Mobile Phone Power Management

Wearable Sensor Node Supply

Use Scenario: Local 1.8 V supply for baseband processor I/O and memory interface in LTE smartphones.

IC Role / Device Role / Timing Role: Low-noise post-regulator stepping down from main PMIC output to meet tight voltage tolerance and noise requirements of high-speed digital interfaces.

Use Value: 55 dB SVR at 1 kHz suppresses ripple from switching PMIC, preventing bit errors in DDR I/O timing margins.

Use Scenario: Primary regulated rail for ultra-low-power BLE SoC and MEMS accelerometer in fitness trackers.

IC Role / Device Role / Timing Role: Always-on LDO providing stable 1.8 V during active sensing and sub-µA shutdown during motionless periods.

Use Value: 85 µA quiescent current and 1.5 µA OFF-mode draw extend coin-cell battery life beyond 12 months.

Industrial IoT Edge Controller

Automotive Infotainment MCU Core

Use Scenario: Dedicated 1.8 V supply for FPGA configuration I/O banks in remote monitoring gateways.

IC Role / Device Role / Timing Role: Local regulator decoupling FPGA I/O from noisy shared 3.3 V system rail, minimizing crosstalk-induced setup/hold violations.

Use Value: 150 mV dropout allows operation from 1.95 V input, enabling direct connection to partially loaded 2.0 V intermediate bus.

Use Scenario: Core voltage rail for ARM Cortex-M7 MCU in head-unit application processors.

IC Role / Device Role / Timing Role: Automotive-grade LDO (AEC-Q100 qualified variant available) delivering 1.8 V with thermal shutdown at 160 °C.

Use Value: Guaranteed -40 °C to +85 °C operation and 250 mV max dropout ensure reliable boot and runtime performance in vehicle cabin environments.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
Torex XC6206P182MR	1.8 V fixed, 300 mA, but higher dropout (300 mV @ 300 mA) and higher noise (50 µV_RMS).	Lacks inhibit pin; requires external enable circuitry for shutdown control.	Choose when cost is primary constraint and system does not require fast turn-on or deep-sleep current <2 µA.
ON Semiconductor NCP114AMX18T2G	1.8 V fixed, 300 mA, 250 mV dropout (typ.), 45 µV_RMS noise, 1.2 µA shutdown current.	Uses different pinout (SOT-23-5 with GND on Pin 2, VO on Pin 5 same; but VINH function absent - uses EN pin with different threshold).	Choose when pin-compatible replacement is needed and 55 dB SVR is not required; verify EN logic compatibility.

Compared with XC6206P182MR and NCP114AMX18T2G, LDS3985M18R offers superior noise performance (30 µV_RMS) and tighter dropout (150 mV typ.), while retaining integrated inhibit control and automotive qualification path-making it optimal for noise-critical, battery-constrained, and thermally demanding designs.

Availability

LDS3985M18R is available at Aetrix Electronics and suitable for mobile phone power management, wearable sensor node supply, and industrial IoT edge controller applications requiring stable component supply, long-lifecycle support, and traceable sourcing.

Supply support for LDS3985M18R 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 smart driving, power management, and embedded processing.

The LDS3985 belongs to ST's high-performance analog LDO portfolio, engineered specifically for ultra-low-noise, low-quiescent-current regulation in battery-powered and thermally constrained systems.

FAQ

What is the minimum input voltage required for stable 1.8 V output at 300 mA?

The LDS3985M18R requires a minimum input voltage of 1.95 V (1.8 V + 150 mV typical dropout) to maintain regulation at 300 mA load. Below 2.5 V input, dropout behavior is not characterized per datasheet Note (3), so design margin should ensure VI ≥ 2.5 V for guaranteed performance across temperature and process variation.

Can the BYPASS pin be left unconnected?

No. The BYPASS pin must be connected to a 10 nF capacitor to ground to stabilize the internal reference and reduce output noise. Leaving it floating degrades noise performance and may cause instability, as confirmed by ST's recommended test conditions and Figure 17 transient response data.

Is the LDS3985M18R qualified for automotive applications?

The LDS3985M18R itself is rated for -40 °C to +125 °C operation and meets industrial reliability standards. For automotive use, ST offers the pin-compatible LDS3985PU18RY variant, which is AEC-Q100 qualified and screened per AEC-Q001/Q002, with identical electrical specs except for the extended temperature range (-40 °C to +85 °C).

What output capacitor ESR range is supported?

The LDS3985M18R is stable with ceramic output capacitors having ESR between 5 mΩ and 5000 mΩ, as specified in Table 5. This wide ESR tolerance eliminates need for specialized low-ESR tantalum or polymer capacitors, enabling cost-effective, space-efficient 2.2 µF X5R/X7R ceramic solutions.

LDS3985M18R 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):: 1.8V

Voltage - Output (Max):: -

Voltage Dropout (Max):: 0.25V @ 300mA

Current - Output:: 300mA

Current - Quiescent (Iq):: 150 µA

Current - Supply (Max):: 300 µA

PSRR:: 55dB ~ 50dB (1kHz ~ 10kHz)

Control Features:: Shutdown

Protection Features:: Over Current, Over Temperature

Operating Temperature:: -40°C ~ 125°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23-5

LDS3985M18R FAQ

1.How can I place an order for LDS3985M18R through Aetrix?

Please submit a Request for Quotation (RFQ) for LDS3985M18R 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 LDS3985M18R reliable?

The price and inventory of LDS3985M18R are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LDS3985M18R is usually 5 days.

3.What payment methods are accepted for LDS3985M18R?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LDS3985M18R transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for LDS3985M18R?

LDS3985M18R orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your LDS3985M18R 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 LDS3985M18R?

For technical support, including LDS3985M18R datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LDS3985M18R requirements.

6.How does Aetrix verify that LDS3985M18R is sourced from the original manufacturer or authorized distributors?

All LDS3985M18R 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 LDS3985M18R meets industry standards.

7.What is the process for return or replacement of LDS3985M18R?

All LDS3985M18R units undergo pre-shipment inspection (PSI). If there is an issue with LDS3985M18R, 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 LDS3985M18R part is unused and in its original packaging.

Return procedure for LDS3985M18R:

1.Submit a request within 90 days.

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

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