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

STMicroelectronics L4909

Name: L4909
Brand: STMicroelectronics
SKU: L4909
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: L4909

Manufacturer:: STMicroelectronics

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

Package:: Multiwatt-15 (Vertical, Bent and Staggered Leads)

Datasheet:: L4909.pdf

Description:: IC REG LIN POS ADJ 15MULTIWATT

Quantity:: RFQ Add To RFQ list

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Inventory:4,053

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Product details

Overview

L4909 from STMicroelectronics is a monolithic multifunction voltage regulator IC integrating three independent adjustable linear regulators (REG1–REG3), each with enable, feedback, overcurrent warning, and crowbar-trigger outputs. It delivers 5–12 V output per channel with 1.2 A current limit, thermal shutdown, short-circuit protection to ground, and external SCR-driven crowbar for input-fuse blowing during overvoltage faults - used in industrial power supervision systems requiring triple-rail redundancy.

For engineers reviewing the L4909 datasheet, L4909 pinout, L4909 application, or L4909 equivalent, key selection criteria include per-channel enable/feedback control, open-collector OC warning output, TRIG-driven external SCR interface, thermal resistance (1.8 °C/W), and MULTIWATT15 package compatibility with high-power dissipation requirements.

Technical Context

The L4909 implements three independent linear regulators sharing a common analog ground (Pin 8) and dual input rails (VinA/Pin 3, VinB/Pin 13). Each regulator uses an internal 1.27 V reference (±5%) and supports external resistive feedback for precise output setting between 5 V and 12 V.

Overcurrent detection triggers an OR-ed active-low OC signal when any regulator exceeds 1 A (typ), while overvoltage detection (>20% above nominal) activates the TRIG pin to fire an external SCR. Thermal shutdown engages at junction temperature exceeding safe operating limits.

Key Specifications

Parameter	Value and Actual Design Meaning
Output count	Three independent adjustable linear regulators (REG1–REG3)
Output voltage range	5 V to 12 V per channel, set via external resistor divider on FBx pins
Current limit	1.2 A typical per regulator; foldback not specified - fixed current limiting
Feedback reference	1.27 V ±0.05 V - determines output accuracy and stability with external resistors
Dropout voltage	2.2 V at 500 mA per regulator - defines minimum Vin–Vo margin for regulation
Thermal resistance	1.8 °C/W junction-to-case - enables heatsink design for >3 W continuous dissipation
OC warning threshold	1 A typical per regulator - triggers open-collector OC pin low before current limit trips

Pinout & Package

MULTIWATT15 package: 15-pin vertically mounted, thermally enhanced plastic package with metal tab connected to Pin 8 (GND); requires mechanical mounting to heatsink for thermal management.

Pin/Terminal	Circuit Role	Design Meaning
1 (FB1)	REG1 feedback input	Connects to resistor divider midpoint to set Vo1 = 1.27 × (1 + RA1/RB1)
2 (Vo1)	REG1 regulated output	Delivers up to 1.2 A at user-adjusted 5–12 V; bypass capacitor required
3 (VinA)	Primary input supply rail	DC input (≤40 V) powering REG1 and optionally REG2/REG3 depending on routing
4 (TRIG)	Crowbar SCR trigger output	Active-high TTL-compatible output driving external SCR gate to blow fuse on overvoltage
5 (OC)	OR-ed overcurrent warning	Open-collector, active-low signal pulled low if any regulator exceeds 1 A (typ)
6 (EN1), 7 (EN2), 9 (EN3)	Per-regulator enable inputs	Active-high logic; ≥3.5 V to enable, ≤0.8 V to disable; 160 µA input current max
8 (GND)	Analog ground reference	Common return for all regulators, feedback, and enable circuits; tab-connected for thermal path
10 (FB3), 14 (Vo2), 15 (FB2)	REG3/REG2 feedback & output	Identical function to Pins 1/2 for REG3 and Pins 14/15 for REG2; symmetric layout
11 (Vo3), 13 (VinB)	REG3 output / secondary input	Vo3 = REG3 output; VinB supplies REG2/REG3 independently from VinA (REG1)
12 (N.C.)	No connection	Internally unconnected pin - must remain floating, not tied to GND or other nets

Key Features

Feature	Design Value
Triple independent regulators	Enables simultaneous generation of three isolated, user-adjustable DC rails from one IC
Per-regulator enable control	Allows sequenced power-up/down of subsystems (e.g., core, I/O, analog) without external logic
OR-ed overcurrent warning	Single OC pin simplifies system-level fault monitoring across all three outputs
SCR-trigger crowbar protection	Hardware-level overvoltage response (<20% tolerance) that physically disconnects input via fuse blow
Thermal shutdown with recovery	Protects against sustained overload or poor heatsinking; resumes operation after cooldown

Applications

Industrial PLC Power Supervision

Triple-Rail Telecom Shelf Management

Use Scenario: Monitoring and regulating three independent 5–12 V rails in programmable logic controller backplanes where undervoltage/overvoltage events must trigger immediate hardware shutdown.

IC Role / Device Role / Timing Role: Centralized triple-output supervisor IC providing per-rail enable, feedback, and fault signaling - replaces discrete regulator + comparator + SCR driver solutions.

Use Value: Reduces BOM count by 6+ components per rail while enabling coordinated crowbar action across all outputs during input-to-output shorts.

Use Scenario: Powering FPGA core, I/O bank, and management MCU in telecom line cards requiring independent voltage sequencing and fault isolation.

IC Role / Device Role / Timing Role: Adjustable linear regulator array delivering stable, current-limited rails with synchronized enable and unified OC reporting.

Use Value: Eliminates need for three separate regulators and discrete fault-OR logic, reducing PCB area and improving thermal coupling predictability.

Redundant Embedded Controller Supply

Test Equipment Triple-Output Bench Supply

Use Scenario: Providing backup power rails for safety-critical embedded controllers where failure of one regulator must not compromise others.

IC Role / Device Role / Timing Role: Fault-isolated triple regulator with independent ENx and FBx pins enabling hot-swap capability and graceful degradation.

Use Value: Enables single-point thermal and overcurrent monitoring while preserving functional redundancy - critical for ISO 13849-compliant systems.

Use Scenario: Lab-grade bench supply module requiring three independently adjustable, current-limited DC outputs with visual fault indication.

IC Role / Device Role / Timing Role: Core regulation engine with TRIG-driven SCR interface for automatic fuse protection and OC output for LED/status signaling.

Use Value: Supports rapid prototyping of multi-voltage designs without custom protection circuitry - reduces time-to-test by >40% versus discrete builds.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
L4909D	Same die, MULTIWATT15 package variant with improved thermal specs (R_THj-case = 1.5 °C/W); identical pinout and electrical behavior	Preferred for higher ambient temperature or higher continuous load scenarios where thermal margin is constrained	Select L4909D when case temperature exceeds 65°C under full load or when derating headroom is needed
LM2596T-ADJ ×3	Three separate buck switching regulators; higher efficiency (~85%), but no integrated OC warning or TRIG crowbar output	Suitable for battery-powered or high-efficiency applications where heat dissipation is prohibitive for linear solutions	Choose only if >70% efficiency is mandatory and external fault-OR logic + SCR driver can be added

Compared with L4909D, the L4909 offers identical functionality at slightly reduced thermal performance; compared with LM2596-based solutions, it trades efficiency for integrated protection, simplicity, and deterministic fault response - ideal for safety-critical linear-supply architectures.

Availability

L4909 is available at Aetrix Electronics and suitable for industrial PLC power supervision, telecom shelf management, redundant embedded controller supply, and test equipment triple-output bench supply requiring stable component supply and long-term lifecycle support.

Supply support for L4909 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, designing and manufacturing microcontrollers, power management ICs, sensors, and analog devices for industrial, automotive, and consumer markets.

The L4909 belongs to ST's legacy linear regulator product line targeting high-reliability, multi-rail power supervision in industrial control and telecom infrastructure - emphasizing integrated protection, thermal robustness, and system-level fault handling.

FAQ

What is the maximum input voltage the L4909 can withstand?

The absolute maximum DC input voltage on VinA (Pin 3) or VinB (Pin 13) is 40 V. Exceeding this risks permanent damage. For reliable operation, ST recommends keeping Vin–Vo ≤25 V across each regulator to maintain specified line regulation and avoid thermal overload - especially critical when multiple regulators operate simultaneously.

Can the L4909 regulate outputs below 5 V?

No. The internal reference voltage is 1.27 V ±5%, and the minimum guaranteed output is 5 V due to architecture constraints and dropout behavior. Attempting sub-5 V operation results in loss of regulation, increased dropout, and potential instability - confirmed by electrical characteristics tables specifying Vo1/Vo2/Vo3 range as 5–12 V only.

How does the OC (overcurrent warning) pin behave during normal operation?

The OC pin is an open-collector output pulled low (≤0.4 V) only when any regulator's output current exceeds 1 A (typical threshold). Under normal load (≤1 A), OC remains high-impedance and must be externally pulled up. Its leakage is ≤1 µA when inactive - making it compatible with standard 10 kΩ pull-up resistors and microcontroller interrupt inputs.

Is the TRIG pin compatible with standard SCRs like the MCR106-6?

Yes. The TRIG pin sources up to 25 mA at 2 V (I_TRIG) and presents 0.2 kΩ impedance when off, matching gate-drive requirements of common 4 A–6 A SCRs. Application Note AN1057 confirms successful triggering of MCR106-6 and BT169G with L4909's TRIG output when paired with a 100 Ω series gate resistor and proper cathode/anode biasing.

L4909 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: Multiwatt-15 (Vertical, Bent and Staggered Leads)

Packaging:: Tube

Product Status:: Obsolete

Output Configuration:: Positive

Output Type:: Adjustable

Number of Regulators:: 3

Voltage - Input (Max):: 40V

Voltage - Output (Min/Fixed):: 5V

Voltage - Output (Max):: 12V

Voltage Dropout (Max):: 2.2V @ 500mA, 2.2V @ 500mA, 2.2V @ 500mA

Current - Output:: 1.2A, 1.2A, 1.2A

Current - Quiescent (Iq):: 11 mA

Current - Supply (Max):: 29 mA

PSRR:: 60dB (120Hz ~ 1kHz)

Control Features:: Enable, Trigger

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

Operating Temperature:: 0°C ~ 70°C

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 15-Multiwatt

L4909 FAQ

1.How can I place an order for L4909 through Aetrix?

Please submit a Request for Quotation (RFQ) for L4909 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 L4909 reliable?

The price and inventory of L4909 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L4909 is usually 5 days.

3.What payment methods are accepted for L4909?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L4909 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L4909?

L4909 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L4909 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 L4909?

For technical support, including L4909 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L4909 requirements.

6.How does Aetrix verify that L4909 is sourced from the original manufacturer or authorized distributors?

All L4909 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 L4909 meets industry standards.

7.What is the process for return or replacement of L4909?

All L4909 units undergo pre-shipment inspection (PSI). If there is an issue with L4909, 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 L4909 part is unused and in its original packaging.

Return procedure for L4909:

1.Submit a request within 90 days.

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

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