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

STMicroelectronics L78L18ACUTR

Name: L78L18ACUTR
Brand: STMicroelectronics
SKU: L78L18ACUTR
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: L78L18ACUTR

Manufacturer:: STMicroelectronics

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

Package:: TO-243AA

Datasheet:: L78L18ACUTR.pdf

Description:: IC REG LINEAR 18V 100MA SOT89-3

Quantity:: RFQ Add To RFQ list

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Inventory:74,194

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Product details

Overview

L78L18ACUTR from STMicroelectronics is a fixed-output +18 V, 100 mA positive linear voltage regulator in SOT-89 package, featuring thermal overload protection, short-circuit current limiting, and ±4% output voltage tolerance at 25 °C. It delivers stable local regulation for microcontroller peripherals, sensor interfaces, and low-power analog circuitry with 1.7 V dropout voltage and 120 µV RMS output noise (10 Hz–100 kHz).

For engineers reviewing the L78L18ACUTR datasheet, L78L18ACUTR pinout, L78L18ACUTR application, or L78L18ACUTR equivalent, this device supports on-card power conditioning where low quiescent current (6.5 mA typ.), high PSRR (33–38 dB at 120 Hz), and no external components are required.

Technical Context

The L78L18ACUTR implements a monolithic three-terminal architecture with internal current limiting and thermal shutdown, eliminating need for external protection circuitry. Its output voltage is factory-trimmed to 18 V with ±4% accuracy over 0–125 °C operating junction temperature range.

It operates with input voltages from 22 V to 33 V (min VI = VO + Vd = 19.7 V), sustaining full 100 mA load while maintaining regulation within 85 mV load regulation (IO = 1–40 mA) and 270 mV line regulation (VI = 22–33 V).

Key Specifications

Parameter	Value and Actual Design Meaning
Output Voltage	+18 V nominal, ±4% tolerance at 25 °C - ensures precise biasing for 18 V logic or analog rails without trimming.
Max Output Current	100 mA - sufficient for powering MCU I/O banks, op-amps, or small-signal sensors without external pass devices.
Dropout Voltage	1.7 V at 40 mA - enables operation from 19.7 V minimum input, reducing heat dissipation vs. higher-dropout regulators.
Quiescent Current	6.5 mA typical at 25 °C - minimizes standby power loss in battery-backed or energy-sensitive systems.
Output Noise	120 µV RMS (10 Hz–100 kHz) - low enough for noise-sensitive analog front-ends like ADC references or precision amplifiers.
PSRR	33–38 dB at 120 Hz - suppresses ripple from unregulated DC/DC or rectified AC sources feeding the input.
Thermal Shutdown	Internally activated - prevents damage during sustained overload or inadequate PCB copper heatsinking.

Pinout & Package

SOT-89 package: 3-pin surface-mount, thermally enhanced plastic case with exposed die attach pad connected internally to Pin 2 (GND). Requires ≥6 cm² copper pour for optimal thermal performance (R_thJA = 55 °C/W).

Pin/Terminal	Circuit Role	Design Meaning
Pin 1 (Input)	VIN	Unregulated DC input (22–33 V); must be decoupled with ≥0.33 µF ceramic capacitor per datasheet.
Pin 2 (Tab/GND)	GND	Power ground and thermal path; electrically tied to exposed tab - must be soldered to large copper area.
Pin 3 (Output)	VOUT	Regulated +18 V output; requires ≥0.1 µF ceramic capacitor for stability and transient response.

Key Features

Feature	Design Value
No external components required	Self-contained regulation with integrated pass transistor, error amplifier, and protection - reduces BOM count and layout area.
±4% output voltage tolerance (A grade)	Tighter than standard C-grade (±8%) - improves system-level voltage margin for 18 V logic or analog supply rails.
Thermal overload and short-circuit protection	Automatic foldback current limiting and junction shutdown - eliminates need for external fuses or current-sense circuitry.
Low output noise (120 µV RMS)	Enables direct use in precision analog signal chains without additional LC filtering stages.
SOT-89 thermal enhancement	Exposed tab bonded to GND and optimized internal frame - achieves R_thJC = 55 °C/W with minimal PCB copper.

Applications

Industrial Sensor Interface

Microcontroller I/O Power

Use Scenario: Powering 18 V analog sensors (e.g., 4–20 mA transmitters, RTD conditioners) in PLC modules or field instruments.

IC Role / Device Role / Timing Role: Local point-of-load regulator providing clean, stable 18 V bias independent of main system rail noise.

Use Value: Eliminates distribution losses and noise coupling from shared 24 V bus, improving sensor measurement accuracy by >0.5% FS.

Use Scenario: Supplying 18 V I/O banks for industrial microcontrollers (e.g., STM32H7, RA6M5) driving optocouplers or level-shifted communication lines.

IC Role / Device Role / Timing Role: Dedicated voltage source for GPIOs requiring 18 V logic compatibility or isolated interface drivers.

Use Value: Prevents I/O voltage droop during simultaneous pin switching, ensuring reliable timing margins for SPI/I²C peripherals.

Portable Test Equipment

Legacy System Voltage Translation

Use Scenario: Battery-powered handheld calibrators needing regulated 18 V for DAC reference buffers or op-amp rails.

IC Role / Device Role / Timing Role: Low-noise, low-quiescent regulator enabling >10-hour runtime on Li-ion packs with minimal heat generation.

Use Value: 120 µV noise and 6.5 mA IQ allow direct connection to 16-bit DAC references without added filtering or LDO post-regulation.

Use Scenario: Retrofitting legacy 18 V logic systems (e.g., older PLC backplanes, relay controllers) with modern replacement regulators.

IC Role / Device Role / Timing Role: Drop-in compatible upgrade for obsolete TO-92 78L18 variants, retaining same footprint and electrical behavior.

Use Value: SOT-89 package offers superior thermal performance vs. TO-92, enabling full 100 mA load without heatsink in space-constrained enclosures.

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-output linear regulator applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
LM78L18ACZ	TO-92 package, ±5% tolerance, 2 V dropout, 150 µV noise, 30–40 dB PSRR	Higher thermal resistance (R_thJA ≈ 200 °C/W) limits continuous 100 mA use without heatsink	Prefer for through-hole prototyping or legacy board rework where SOT-89 reflow is unavailable
TL78L18ACDR	SOT-23-5 package, ±4% tolerance, 1.8 V dropout, 100 µV noise, 35–40 dB PSRR	Lower max current (75 mA), no internal short-circuit foldback - requires external current limiting	Choose when board space is critical and load current stays ≤75 mA with known safe thermal profile

Compared with LM78L18ACZ and TL78L18ACDR, the L78L18ACUTR provides superior thermal performance in SOT-89, guaranteed 100 mA delivery with robust internal protection, and tighter noise/PSRR specs - making it optimal for industrial embedded designs demanding reliability and low-noise operation.

Availability

L78L18ACUTR is available at Aetrix Electronics and suitable for industrial sensor interfaces, microcontroller I/O power, portable test equipment, and legacy system voltage translation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for L78L18ACUTR 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, specializing in automotive, industrial, and power management ICs with strong emphasis on reliability and longevity.

The L78L series belongs to ST's legacy linear regulator product line, designed specifically for cost-sensitive, high-volume industrial and consumer applications requiring robustness, simplicity, and wide ambient temperature operation.

FAQ

What is the minimum input voltage required for L78L18ACUTR to maintain regulation?

The minimum input voltage is 19.7 V, calculated as VO + Vd = 18 V + 1.7 V dropout. Operation below this threshold causes output voltage to track input, losing regulation. Datasheet specifies valid input range as 22–33 V for full 100 mA load and 0–125 °C junction temperature.

Can L78L18ACUTR be used in parallel to increase output current?

No - the L78L18ACUTR lacks current-sharing capability and has no built-in balancing features. Parallel connection risks thermal runaway due to mismatched output voltages and unequal current division. For >100 mA, use an external pass transistor per Figure 14 in DS0424.

Is the SOT-89 tab electrically connected, and how should it be handled on the PCB?

Yes, the exposed tab is internally connected to Pin 2 (GND). It must be soldered to a ≥6 cm² copper pour acting as both electrical ground and thermal heatsink. Isolating the tab or using insufficient copper increases junction temperature beyond 125 °C, triggering thermal shutdown under load.

Does L78L18ACUTR require input/output capacitors, and what values are validated?

Yes - CI = 0.33 µF ceramic (X7R) at VIN and CO = 0.1 µF ceramic (X7R) at VOUT are mandatory per DS0424 test circuits. Omitting either causes instability or excessive output ripple. Tantalum or electrolytic capacitors are not recommended due to ESR-related phase margin degradation.

L78L18ACUTR 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):: 40V

Voltage - Output (Min/Fixed):: 18V

Voltage - Output (Max):: -

Voltage Dropout (Max):: -

Current - Output:: 100mA

Current - Quiescent (Iq):: 6 mA

Current - Supply (Max):: 6.5 mA

PSRR:: 38dB (120Hz)

Control Features:: -

Protection Features:: Over Current, Over Temperature, Short Circuit

Operating Temperature:: 0°C ~ 125°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-89-3

L78L18ACUTR FAQ

1.How can I place an order for L78L18ACUTR through Aetrix?

Please submit a Request for Quotation (RFQ) for L78L18ACUTR 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 L78L18ACUTR reliable?

The price and inventory of L78L18ACUTR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L78L18ACUTR is usually 5 days.

3.What payment methods are accepted for L78L18ACUTR?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L78L18ACUTR transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L78L18ACUTR?

L78L18ACUTR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L78L18ACUTR 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 L78L18ACUTR?

For technical support, including L78L18ACUTR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L78L18ACUTR requirements.

6.How does Aetrix verify that L78L18ACUTR is sourced from the original manufacturer or authorized distributors?

All L78L18ACUTR 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 L78L18ACUTR meets industry standards.

7.What is the process for return or replacement of L78L18ACUTR?

All L78L18ACUTR units undergo pre-shipment inspection (PSI). If there is an issue with L78L18ACUTR, 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 L78L18ACUTR part is unused and in its original packaging.

Return procedure for L78L18ACUTR:

1.Submit a request within 90 days.

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

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