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

STMicroelectronics LD3985J18R

Name: LD3985J18R
Brand: STMicroelectronics
SKU: LD3985J18R
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: LD3985J18R

Manufacturer:: STMicroelectronics

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

Package:: 5-WFBGA, FCBGA

Datasheet:: LD3985J18R.pdf

Description:: IC REG LIN 1.8V 150MA 5FLIPCHIP

Quantity:: RFQ Add To RFQ list

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Inventory:294

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Product details

Overview

LD3985J18R from STMicroelectronics is a 1.8 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, draws only 85 µA quiescent current at no load, and is optimized for battery-powered RF and sensor subsystems in mobile handsets.

For engineers reviewing the LD3985J18R datasheet, LD3985J18R pinout, LD3985J18R application, or LD3985J18R equivalent, key selection criteria include its low-noise performance, stable operation with 1 µF ceramic output capacitors, guaranteed 150 mA output under -40 °C to 125 °C junction temperature, and integrated thermal/current protection - critical for space-constrained portable electronics.

Technical Context

The LD3985J18R uses BiCMOS process technology to achieve ultra-low dropout (0.4 mV typ. at 1 mA) and sub-100 µA quiescent current while maintaining high PSRR (60 dB at 1 kHz). Its internal architecture includes a precision bandgap reference, error amplifier, and PMOS pass transistor with dedicated bypass pin for noise filtering.

Shutdown is controlled via VINH pin with TTL-compatible thresholds (ON ≥ 1.2 V, OFF ≤ 0.4 V); the device enters <1.5 µA OFF-mode current. Output stability is ensured with low-ESR ceramic capacitors (1–22 µF, ESR 5–5000 mΩ), eliminating need for tantalum or electrolytic types.

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 low-voltage MCUs and RF ICs
Max output current	150 mA guaranteed - sufficient for powering baseband processors or Bluetooth SoCs in compact designs
Dropout voltage	60 mV typ. at 150 mA - enables regulation down to 1.86 V input, extending battery runtime in single-cell Li-ion systems
Output noise	30 µV_RMS (10 Hz–100 kHz) - meets stringent noise requirements for ADC references and RF synthesizer supplies
PSRR	60 dB at 1 kHz, 50 dB at 10 kHz - suppresses switching noise from DC-DC converters feeding intermediate rails
Quiescent current	85 µA typ. at no load; 170 µA typ. at 150 mA - minimizes standby power loss in always-on sensor nodes
Shutdown current	1.5 µA max. - enables deep-sleep modes without external disconnect switches

Pinout & Package

LD3985J18R is housed in a RoHS-compliant SOT23-5L package (2.95 mm × 1.60 mm × 1.30 mm), optimized for high-density PCB layouts and reflow compatibility.

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 control circuitry; must be low-impedance
3 (VINH)	Logic enable/disable input	TTL-compatible control: ≥1.2 V = ON, ≤0.4 V = OFF; must not float; draws ±1 nA
4 (BYPASS)	Noise reduction terminal	Connects to 10 nF capacitor to shunt high-frequency noise from internal reference amplifier
5 (VO)	Regulated output	Delivers stable 1.8 V ±2%; requires ≥1 µF ceramic capacitor (X5R/X7R) for stability

Key Features

Feature	Design Value
Ultra-low dropout	60 mV at 150 mA load - sustains regulation during battery voltage sag in portable devices
Low-noise regulation	30 µV_RMS output noise - eliminates need for post-LDO LC filtering in sensitive analog signal chains
Fast turn-on time	200 µs typical - supports rapid wake-up sequences in duty-cycled IoT endpoints
Thermal & current protection	Internal shutdown at 160 °C with 20 °C hysteresis and current limiting - prevents damage during overload or poor heatsinking
Ceramic capacitor compatible	Stable with 1–22 µF, 5–5000 mΩ ESR ceramics - reduces BOM cost and board area vs. tantalum alternatives

Applications

Mobile Phone Baseband Power

Wearable Sensor Node Supply

Use Scenario: Powers ARM Cortex-M0+ MCU and BLE radio in slim smartphone modules where input rail varies from 3.0–4.2 V during Li-ion discharge.

IC Role / Device Role / Timing Role: Local LDO providing clean 1.8 V core voltage with fast transient response to burst-mode RF transmission.

Use Value: 60 dB PSRR at 1 kHz rejects noise from adjacent buck converters; 85 µA quiescent current extends standby time beyond 30 days.

Use Scenario: Supplies MEMS accelerometer and ultra-low-power ADC in coin-cell–powered fitness tracker operating at -20 °C to 70 °C ambient.

IC Role / Device Role / Timing Role: Primary voltage regulator enabling deep-sleep mode with <1.5 µA shutdown current and 200 µs wake-up latency.

Use Value: Stable 1.8 V output across temperature ensures consistent ADC reference accuracy; 30 µV_RMS noise avoids signal corruption in 16-bit measurements.

Industrial Wireless Sensor Transmitter

Automotive Infotainment Subsystem

Use Scenario: Provides regulated 1.8 V to LoRaWAN transceiver IC in IP67-rated environmental monitor deployed in remote field locations.

IC Role / Device Role / Timing Role: Fault-tolerant local regulator with thermal shutdown and wide -40 °C to 125 °C operating range.

Use Value: Guaranteed 150 mA output supports peak transmit current; 100 mV dropout margin allows operation down to 1.9 V input during cold cranking events.

Use Scenario: Supplies 1.8 V I/O rail for automotive-grade FPGA configuration memory and display interface logic in head unit design.

IC Role / Device Role / Timing Role: Secondary LDO decoupling high-speed digital interfaces from noisy main 5 V/3.3 V domains.

Use Value: 50 dB PSRR at 10 kHz suppresses switching artifacts from DC-DC controllers; SOT23-5L footprint fits tight routing constraints near BGA packages.

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	150 mA output, 250 mV dropout at 150 mA, 45 µV_RMS noise, SOT23-3 package (no shutdown)	Lacks logic-controlled shutdown and bypass pin; limited to simpler always-on use cases	Select when board space is critical and shutdown functionality is handled externally
ROHM BD3985FV-ME2	150 mA output, 120 mV dropout at 150 mA, 40 µV_RMS noise, built-in soft-start, same SOT23-5L pinout	Higher dropout reduces usable input range; soft-start adds 1.2 ms delay but improves inrush control	Prefer when inrush current limiting is required and 1.86 V minimum input is acceptable

Compared with XC6206P182MR and BD3985FV-ME2, LD3985J18R delivers the lowest dropout and noise among the three, making it optimal for battery-critical and noise-sensitive applications - though its lack of soft-start requires careful sequencing in multi-rail systems.

Availability

LD3985J18R is available at Aetrix Electronics and suitable for mobile handset power management, wearable health monitors, industrial wireless sensors, and automotive infotainment subsystems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD3985J18R 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 components for industrial, automotive, and consumer markets.

LD3985 belongs to ST's ultra-low-noise, low-quiescent-current LDO family targeting battery-powered portable electronics - engineered specifically for RF coexistence, extended battery life, and minimal PCB footprint in space-constrained designs.

FAQ

What is the minimum input voltage required for LD3985J18R to maintain regulation?

The LD3985J18R maintains 1.8 V output regulation as long as input voltage remains ≥ (1.8 V + dropout voltage). At 150 mA load, typical dropout is 60 mV, so minimum VI is 1.86 V. At lighter loads (e.g., 1 mA), dropout drops to 0.4 mV, allowing regulation down to 1.8004 V - critical for end-of-discharge battery operation.

Can LD3985J18R operate without the BYPASS capacitor?

No. The BYPASS pin must be connected to a 10 nF ceramic capacitor to stabilize the internal reference amplifier and achieve specified 30 µV_RMS noise performance. Omitting this capacitor increases output noise by >3× and may cause instability under certain load transients, per Section 5.1 of the datasheet.

Is LD3985J18R pin-compatible with other SOT23-5L LDOs?

LD3985J18R follows standard SOT23-5L pinout (VI-GND-VINH-BYPASS-VO), matching industry layout conventions. However, functionally identical pin mapping does not guarantee drop-in replacement due to differences in shutdown threshold, PSRR profile, and thermal behavior - validation against target load and noise requirements is essential.

What is the maximum allowable output capacitor ESR for stable operation?

The LD3985J18R is stable with output capacitors having ESR between 5 mΩ and 5000 mΩ, as confirmed in Table 4 footnote 6 and Section 7.1. Unlike older LDOs, it does not require minimum ESR, enabling use of low-ESR X5R/X7R ceramics (typ. 5–20 mΩ) without risk of oscillation - simplifying design and reducing cost.

LD3985J18R Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 5-WFBGA, FCBGA

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

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):: -

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:: 5-FlipChip (1.59x1.24)

LD3985J18R FAQ

1.How can I place an order for LD3985J18R through Aetrix?

Please submit a Request for Quotation (RFQ) for LD3985J18R 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 LD3985J18R reliable?

The price and inventory of LD3985J18R are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LD3985J18R is usually 5 days.

3.What payment methods are accepted for LD3985J18R?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LD3985J18R transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for LD3985J18R?

LD3985J18R orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your LD3985J18R 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 LD3985J18R?

For technical support, including LD3985J18R datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LD3985J18R requirements.

6.How does Aetrix verify that LD3985J18R is sourced from the original manufacturer or authorized distributors?

All LD3985J18R 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 LD3985J18R meets industry standards.

7.What is the process for return or replacement of LD3985J18R?

All LD3985J18R units undergo pre-shipment inspection (PSI). If there is an issue with LD3985J18R, 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 LD3985J18R part is unused and in its original packaging.

Return procedure for LD3985J18R:

1.Submit a request within 90 days.

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

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