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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Voltage Regulators - DC DC Switching Regulators

STMicroelectronics L5971D

Name: L5971D
Brand: STMicroelectronics
SKU: L5971D
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: L5971D

Manufacturer:: STMicroelectronics

Category:: Voltage Regulators - DC DC Switching Regulators

Package:: 16-SOIC (0.295", 7.50mm Width)

Datasheet:: L5971D.pdf

Description:: IC REG BUCK ADJ 1.5A 16SO W

Quantity:: RFQ Add To RFQ list

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Inventory:3,576

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Product details

Overview

L5971D from STMicroelectronics is a monolithic step-down DC-DC switching regulator delivering up to 1.5A output current, operating from 6.5V to 28V input, with adjustable output voltage (1.26V–20V) and internal 1.26V ±1% reference. It integrates a 0.25Ω D-MOS power transistor and supports up to 300kHz switching frequency. Used in portable computers and battery chargers for high-efficiency local regulation.

For engineers reviewing the L5971D datasheet, L5971D pinout, L5971D application, or L5971D equivalent, key selection considerations include its voltage feedforward architecture, pulse-by-pulse current limiting, soft-start timing via external capacitor, thermal shutdown behavior, and SO16 package thermal resistance of 110°C/W.

Technical Context

The L5971D implements voltage-mode control with feedforward compensation, where oscillator ramp amplitude scales with input voltage to improve line regulation and transient response. Its error amplifier features 57dB open-loop gain and 4.3mS transconductance, enabling stable loop compensation via external RC network on COMP pin.

Switching is driven by an internal PWM comparator comparing the error amplifier output against a temperature-stable oscillator ramp (±4% over 0–125°C). The BOOT pin enables high-side gate drive using an external bootstrap capacitor, while FB pin accepts direct connection or resistive divider for output voltage setting.

Key Specifications

Parameter	Value and Actual Design Meaning
Input Voltage Range	6.5V to 28V - supports wide industrial and automotive battery-supplied systems without pre-regulation.
Output Current	Up to 1.5A continuous - sufficient for core logic rails in portable computing and PDA applications.
Reference Voltage	1.26V ±1% - enables precise output setting; tolerance directly impacts output accuracy across temperature and load.
Switching Frequency	Adjustable up to 300kHz - higher frequencies allow smaller magnetics but require attention to SO16 thermal limits (0.8W max).
R_DS(on)	0.25Ω typical - reduces conduction loss at full load, contributing to >85% efficiency at 3.3V/1.5A.
Quiescent Current	4.5mA typical operating, 200µA standby - enables low-power sleep mode during system idle periods.
Thermal Resistance	110°C/W (Junction-to-Ambient, SO16) - defines maximum power dissipation (0.8W) before thermal shutdown activates.

Pinout & Package

Package: SO16 Wide (10.1 × 7.4 mm body, 1.27 mm pitch), surface-mount, RoHS-compliant plastic package with exposed pad not electrically connected.

Pin/Terminal	Circuit Role	Design Meaning
1 (GND)	Power Ground Reference	Common return path for internal circuitry and external feedback network; must be low-impedance connection.
2 (SS_INH)	Soft-Start / Inhibit Control	Active-low enable; capacitor to GND sets soft-start time; grounding forces zero-current shutdown mode.
3 (OSC)	Oscillator Timing Node	External R+C sets switching frequency; inherent voltage feedforward achieved via internal scaling.
4,5 (OUT)	Power Switch Output	Drives external inductor; dual pins reduce trace inductance and improve current sharing in high-frequency operation.
6 (BOOT)	Bootstrap Gate Drive	Connects external capacitor between BOOT and OUT to generate gate voltage > V_IN for internal high-side MOSFET.
7 (COMP)	Error Amplifier Output	Provides compensation node for external Type-II/III network to stabilize control loop bandwidth and phase margin.
8 (FB)	Voltage Feedback Input	Compares output voltage (direct or via divider) against 1.26V reference; open-loop disconnect triggers protection.
11 (VCC)	Unregulated Input Supply	Primary power input for internal bias and gate drivers; must be decoupled locally with ≥47µF low-ESR capacitor.
12 (BOOT)	Bootstrap Gate Drive	Duplicate of Pin 6 - internally tied; both pins used for parallel routing to minimize impedance.
13 (COMP)	Error Amplifier Output	Duplicate of Pin 7 - internally tied; improves layout flexibility for compensation network placement.
14 (FB)	Voltage Feedback Input	Duplicate of Pin 8 - internally tied; allows redundant feedback routing for noise immunity in noisy environments.
15,16 (NC)	No Connect	Not bonded; no internal connection - must remain unconnected per datasheet guidance.

Key Features

Feature	Design Value
Voltage Feedforward Regulation	Improves line transient response and reduces output deviation under input voltage steps without requiring complex loop redesign.
Pulse-by-Pulse Current Limiting	Prevents MOSFET destruction during overload or short-circuit by disabling each switching cycle exceeding ~2.5A peak current.
Hiccup Mode Short-Circuit Protection	After repeated current-limit events, device enters low-duty-cycle restart cycle to limit average power dissipation and prevent thermal runaway.
Feedback Disconnection Protection	Automatically shuts down if FB pin floats or opens, avoiding uncontrolled high-voltage output conditions.
Zero-Current Inhibit Function	Reduces total supply current to ≤200µA when SS_INH is pulled low, enabling true system-level power gating.

Applications

Portable Computer Power Rails

Battery Charger Auxiliary Supply

Use Scenario: Generating 3.3V/1.5A core voltage for embedded controllers in clamshell laptops with 12–24V battery input.

IC Role / Device Role / Timing Role: Primary step-down regulator providing stable, efficient local power with fast line/load transient response.

Use Value: Delivers >85% efficiency at 3.3V/1.5A and maintains ±1% output accuracy across temperature, reducing thermal load on compact PCBs.

Use Scenario: Providing isolated 5.1V bias for charge management ICs in multi-cell Li-ion battery chargers powered from 18V DC adapters.

IC Role / Device Role / Timing Role: Secondary regulated supply ensuring accurate reference and gate drive for charging FETs and ADCs.

Use Value: Adjustable output (via 12kΩ/3.6kΩ divider) and feedforward control maintain tight regulation despite adapter ripple and load steps.

Distributed Power in Industrial Controllers

PDA System-on-Module Core Supply

Use Scenario: Converting 24V backplane voltage to 2.5V/1.5A for FPGA I/O banks and microcontroller peripherals in DIN-rail mounted PLCs.

IC Role / Device Role / Timing Role: Local point-of-load regulator minimizing voltage drop and EMI from long traces in noisy factory environments.

Use Value: SO16 package with duplicated FB/COMP/BOOT pins improves noise immunity; hiccup mode prevents latch-up during field-induced shorts.

Use Scenario: Supplying 1.8V/1.5A to ARM-based application processors in handheld PDAs with 6–12V battery packs.

IC Role / Device Role / Timing Role: High-efficiency buck converter supporting dynamic voltage scaling and deep-sleep modes.

Use Value: Soft-start (via 100nF SS_INH cap) prevents inrush into large output capacitance; 200µA standby current extends battery life during suspend.

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
LM2596S-ADJ	Fixed 150kHz frequency, no voltage feedforward, higher R_DS(on) (0.35Ω), no hiccup mode	Lacks precision line regulation and robust short-circuit recovery; suited for cost-sensitive non-critical rails	Select if board space allows larger inductor and thermal design accommodates lower efficiency.
MP1584EN-LF-Z	Higher 1.5MHz switching, integrated compensation, no BOOT pin, 0.18Ω R_DS(on), no feedback disconnect protection	Enables smaller magnetics but lacks fault detection for open-feedback scenarios common in field-replaceable modules	Select for compact designs where feedback integrity is ensured by mechanical interlock or redundancy.

Compared with LM2596S-ADJ and MP1584EN-LF-Z, the L5971D offers superior line regulation via feedforward, dedicated protection against feedback failure, and hiccup-mode recovery-making it preferred for industrial and portable systems requiring reliability over minimal BOM cost.

Availability

L5971D is available at Aetrix Electronics and suitable for portable computer power rails, battery charger auxiliary supplies, and distributed power in industrial controllers requiring stable component supply and long-term lifecycle support.

Supply support for L5971D 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 analog, power, microcontroller, and sensor solutions for industrial, automotive, and consumer markets.

The L5971D belongs to ST's legacy power management IC portfolio targeting high-reliability DC-DC conversion in battery-powered and wide-input industrial equipment.

FAQ

What is the minimum recommended output capacitor for stable operation at 1.5A?

The datasheet specifies a minimum 47µF/30V low-ESR electrolytic capacitor at the output, paired with 47nF and 100nF ceramic capacitors for high-frequency filtering. Using less than 47µF risks instability under full load due to insufficient bulk energy storage and degraded phase margin.

How does the L5971D handle input voltage dropout below 6.5V?

Below 6.5V, the device ceases switching and enters undervoltage lockout (UVLO); output collapses as internal bias rails fall out of specification. No brown-out hysteresis is implemented - recovery occurs only after V_CC exceeds 6.8V (typical) with hysteresis of ~0.3V.

Can the L5971D operate without an external bootstrap capacitor?

No. The internal high-side MOSFET requires gate drive above the output voltage, supplied via the BOOT–OUT capacitor. Omitting this capacitor prevents proper switching, resulting in no output regulation and potential thermal stress on the die.

What is the purpose of the duplicated FB, COMP, and BOOT pins in the SO16 package?

Duplicated pins (FB/14, COMP/13, BOOT/12) are internally bonded together to reduce parasitic inductance and improve noise immunity. They allow separate routing paths for feedback sensing, compensation network, and bootstrap charge - critical for stable operation in electrically noisy industrial environments.

L5971D Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 16-SOIC (0.295", 7.50mm Width)

Packaging:: Tube

Product Status:: Obsolete

Function:: Step-Down

Output Configuration:: Positive

Topology:: Buck

Output Type:: Adjustable

Number of Outputs:: 1

Voltage - Input (Min):: 6.5V

Voltage - Input (Max):: 28V

Voltage - Output (Min/Fixed):: 1.26V

Voltage - Output (Max):: 20V

Current - Output:: 1.5A

Frequency - Switching:: 100kHz ~ 300kHz

Synchronous Rectifier:: No

Operating Temperature:: -40°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 16-SO W

L5971D FAQ

1.How can I place an order for L5971D through Aetrix?

Please submit a Request for Quotation (RFQ) for L5971D 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 L5971D reliable?

The price and inventory of L5971D are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L5971D is usually 5 days.

3.What payment methods are accepted for L5971D?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L5971D transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L5971D?

L5971D orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L5971D 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 L5971D?

For technical support, including L5971D datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L5971D requirements.

6.How does Aetrix verify that L5971D is sourced from the original manufacturer or authorized distributors?

All L5971D 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 L5971D meets industry standards.

7.What is the process for return or replacement of L5971D?

All L5971D units undergo pre-shipment inspection (PSI). If there is an issue with L5971D, 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 L5971D part is unused and in its original packaging.

Return procedure for L5971D:

1.Submit a request within 90 days.

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

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