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

STMicroelectronics L7981A

Name: L7981A
Brand: STMicroelectronics
SKU: L7981A
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: L7981A

Manufacturer:: STMicroelectronics

Category:: Voltage Regulators - DC DC Switching Regulators

Package:: 8-SOIC (0.154", 3.90mm Width) Exposed Pad

Datasheet:: L7981A.pdf

Description:: IC REG BUCK ADJ 3A 8HSOP

Quantity:: RFQ Add To RFQ list

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Product details

Overview

L7981A from STMicroelectronics is a 3 A step-down switching regulator with integrated P-channel MOSFET, designed as a primary DC-DC power conversion stage in mid-power embedded systems. It operates from 4.5 V to 28 V input, delivers adjustable output down to 0.6 V, features 250 kHz–1 MHz programmable switching frequency, internal soft-start, and supports zero-load operation - used in LCD TV power rails and FPGA core supplies.

For engineers reviewing the L7981A datasheet, L7981A pinout, L7981A application, or L7981A equivalent, key selection criteria include its voltage-mode control architecture, feed-forward compensation for line/load transient immunity, thermal shutdown hysteresis (150 °C trip / 130 °C recovery), and dual-package support (VFQFPN 3×3–8L and HSOP8) enabling board-level thermal optimization.

Technical Context

The L7981A implements voltage-mode PWM control with a sawtooth oscillator whose slope is dynamically adjusted via voltage feed-forward (input-dependent ramp scaling) and frequency feed-forward (FSW-resistor–adjusted ramp scaling), maintaining constant PWM gain across input voltage and switching frequency variations. Its error amplifier provides 100 dB open-loop gain, 4.5 MHz GBWP, and rail-to-rail output swing (0–3.3 V) for stable loop compensation.

Synchronization is implemented through the SYNCH pin: when floating, it outputs a 180° phase-shifted clock; when externally driven above internal frequency, it locks with zero phase shift; when two devices are daisy-chained, the higher-frequency unit acts as master, enforcing half-cycle interleaving to reduce input capacitor RMS current. Overcurrent protection uses blanking time (~200 ns) and hiccup-mode recovery during regulation, plus pulse-skipping current limiting during soft-start.

Key Specifications

Parameter	Value and Actual Design Meaning
Output current	3 A continuous DC load current - sufficient for FPGA I/O banks or LCD bias supplies without external boost stages.
Input voltage range	4.5 V to 28 V - compatible with 5 V, 12 V, and 24 V industrial bus rails and automotive battery-supplied systems.
Output voltage adjustability	0.6 V to VIN - enables generation of sub-1 V core voltages (e.g., 0.85 V for low-power microcontrollers) using external resistor divider.
Switching frequency	250 kHz (default) up to 1 MHz - higher frequencies allow smaller magnetics and faster transient response; lower frequencies improve light-load efficiency.
MOSFET R_DS(on)	160–250 mΩ (typ. 180 mΩ) - determines conduction loss at full load; combined with 3.7 A min. current limit ensures robust short-circuit handling.
Feedback reference	0.6 V ±1.2% (0.593–0.607 V) - sets output accuracy baseline; external resistor divider ratio directly defines output tolerance budget.
Soft-start duration	7.4–9.1 ms (FSW floating) - prevents inrush current into bulk capacitors; scales inversely with switching frequency (e.g., ~3.5 ms at 1 MHz).

Pinout & Package

Available in VFQFPN 3 × 3 mm – 8L (exposed pad, R_thJA = 60 °C/W) and HSOP8 (exposed pad, R_thJA = 40 °C/W) packages - both optimized for thermal dissipation in space-constrained power designs.

Pin/Terminal	Circuit Role	Design Meaning
OUT	Power switch output node	Connects to inductor and output filter; carries high di/dt switching current - requires short, wide PCB trace and ground plane coupling.
SYNCH	Master/slave synchronization I/O	Accepts external clock (≥ internal FSW) or outputs phase-inverted signal; enables interleaved operation of multiple L7981A for reduced input ripple.
EN	Enable control input (active-high)	Logic threshold: <0.3 V = OFF (<30 µA quiescent), >1.2 V = ON; internal pull-down ensures safe default-off state if unconnected.
COMP	Error amplifier output	Provides access to EA output for external Type II/III compensation network - must be decoupled from noise sources and routed away from switching nodes.
FB	Feedback sensing input	Monitors output via resistor divider; 0.6 V reference sets regulation point - high-impedance node requiring guard ring and minimal trace length.
FSW	Frequency setting/resistor interface	Connect external resistor to GND to scale switching frequency up to 1 MHz; floating = 250 kHz free-run mode.
GND	Power and signal reference	Must be tied to exposed pad and connected to low-impedance ground plane - critical for thermal performance and EMI suppression.
VCC	Unregulated input supply	Supplies internal circuitry and gate driver; requires local 100 nF–1 µF ceramic bypass capacitor placed adjacent to pin.

Key Features

Feature	Design Value
Voltage feed-forward compensation	Adjusts sawtooth slope proportionally to V_IN, maintaining constant PWM gain and improving line transient rejection without additional compensation components.
Zero-load operation capability	Stable regulation down to 0 A output current - eliminates need for dummy loads in always-on systems like set-top box standby rails.
100% duty cycle low-dropout mode	Enables V_OUT ≈ V_IN operation (e.g., 12 V → 11.5 V) by holding high-side MOSFET fully on - useful for post-regulation or battery-saver configurations.
Hysteretic thermal shutdown	Shuts down at 150 °C junction temperature and auto-restarts at ~130 °C - prevents thermal runaway while allowing recovery after brief overloads without system reset.
Integrated soft-start with 64-step ramp	Generates monotonic V_OUT rise using staircase reference (9.5 mV/step), eliminating output overshoot and reducing stress on downstream capacitors.

Applications

Consumer LCD TV Power Supply

FPGA Core Voltage Regulation

Use Scenario: Generating 3.3 V and 1.2 V rails from 12 V main supply in flat-panel TV mainboard.

IC Role / Device Role / Timing Role: Primary buck converter delivering 3 A at 3.3 V for audio/video SoC I/O and memory interfaces.

Use Value: Integrated MOSFET and feed-forward control minimize component count and improve dynamic response to burst video load changes.

Use Scenario: Providing tightly regulated 1.0 V core supply to Xilinx Spartan-7 FPGA under varying logic utilization.

IC Role / Device Role / Timing Role: Constant-frequency voltage-mode buck regulator with 0.6 V feedback reference and programmable 500 kHz switching.

Use Value: 100% duty cycle mode supports brownout hold-up; soft-start prevents configuration bitstream corruption during power-up.

Industrial PLC I/O Module

DSL Modem DC-DC Conversion

Use Scenario: Converting 24 V field bus to isolated 5 V and 3.3 V for digital I/O conditioning circuits.

IC Role / Device Role / Timing Role: Non-isolated step-down regulator operating across wide input range (4.5–28 V) with thermal robustness.

Use Value: HSOP8 package's 40 °C/W R_thJA sustains full 3 A output in enclosed enclosures without forced air cooling.

Use Scenario: Generating 3.3 V and 1.8 V from 12 V adapter in ADSL/VDSL modem power tree.

IC Role / Device Role / Timing Role: High-efficiency synchronous buck controller driving external MOSFETs in compact footprint.

Use Value: SYNCH pin enables interleaving with secondary buck stage to halve input capacitor RMS current and extend capacitor lifetime.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
LM2678-3.3/NOPB	Fixed 3.3 V output, 5 A rating, no programmable frequency, no SYNCH pin, larger SOIC-8 package.	Best for cost-sensitive fixed-output designs where layout space and synchronization are not required.	Select when output voltage is static and thermal constraints are relaxed - lacks L7981A's adjustability and thermal performance.
TPS54331DR	3 A, 3.5–28 V input, adjustable output, 570 kHz fixed frequency, no voltage feed-forward, smaller WSON-8 package.	Suitable for high-density layouts but exhibits poorer line transient response due to absence of feed-forward compensation.	Choose for space-constrained designs needing high integration - trade off transient immunity for footprint reduction.

Compared with LM2678-3.3/NOPB and TPS54331DR, the L7981A uniquely combines programmable frequency, voltage feed-forward, and dual-package thermal options - making it optimal for systems demanding dynamic load handling, EMI control via frequency tuning, and reliable operation in thermally aggressive environments.

Availability

L7981A is available at Aetrix Electronics and suitable for LCD TV power rails, FPGA core supplies, industrial PLC I/O modules, and DSL modem DC-DC conversion requiring stable component supply across multi-year production cycles.

Supply support for L7981A 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, specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

The L7981A belongs to ST's high-current monolithic buck regulator product line, engineered for robust, low-component-count DC-DC conversion in thermally demanding embedded power applications - emphasizing reliability, thermal resilience, and design flexibility.

FAQ

What is the minimum output voltage achievable with the L7981A?

The L7981A has an internal 0.6 V feedback reference voltage with ±1.2% tolerance (0.593–0.607 V). With proper resistor divider design and layout, it reliably regulates down to exactly 0.6 V - confirmed in electrical characteristics Table 4 and functional description Section 5.3. No external reference or trimming is needed to achieve this minimum.

Does the L7981A support forced continuous conduction mode (FCCM)?

No, the L7981A operates exclusively in voltage-mode PWM with automatic discontinuous conduction mode (DCM) entry at light loads. It does not include a mode-select pin or internal circuitry to force CCM. DCM operation reduces light-load quiescent current to 20–30 µA and improves efficiency below ~10% load - verified in Electrical Characteristics Table 4 (I_QST-BY) and Functional Description Section 5.2.

Can the L7981A drive an external N-channel MOSFET instead of using its internal P-channel switch?

No - the L7981A integrates a single P-channel high-side MOSFET and lacks gate-drive outputs or bootstrap circuitry required for external N-channel FET control. Its OUT pin connects directly to the drain of the internal MOSFET; attempting to substitute an external FET would violate the internal current-sense and protection architecture - confirmed in Block Diagram Figure 3 and Functional Description Section 5.

How does the SYNCH pin behave when left unconnected?

When the SYNCH pin is left floating, it outputs a square wave synchronized to the internal oscillator with a precise 180° phase shift relative to the power switch turn-on edge - enabling natural interleaving when two L7981A devices share the same input rail. This behavior is explicitly defined in Pin Description Table 1 and Functional Description Section 5.1, and requires no pull-up or pull-down.

L7981A Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 8-SOIC (0.154", 3.90mm Width) Exposed Pad

Packaging:: Tube

Product Status:: Obsolete

Function:: Step-Down

Output Configuration:: Positive

Topology:: Buck

Output Type:: Adjustable

Number of Outputs:: 1

Voltage - Input (Min):: 4.5V

Voltage - Input (Max):: 28V

Voltage - Output (Min/Fixed):: 0.6V

Voltage - Output (Max):: 28V

Current - Output:: 3A

Frequency - Switching:: 250kHz ~ 1MHz

Synchronous Rectifier:: No

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

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 8-HSOP

L7981A FAQ

1.How can I place an order for L7981A through Aetrix?

Please submit a Request for Quotation (RFQ) for L7981A 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 L7981A reliable?

The price and inventory of L7981A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L7981A is usually 5 days.

3.What payment methods are accepted for L7981A?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L7981A transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L7981A?

L7981A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L7981A 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 L7981A?

For technical support, including L7981A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L7981A requirements.

6.How does Aetrix verify that L7981A is sourced from the original manufacturer or authorized distributors?

All L7981A 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 L7981A meets industry standards.

7.What is the process for return or replacement of L7981A?

All L7981A units undergo pre-shipment inspection (PSI). If there is an issue with L7981A, 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 L7981A part is unused and in its original packaging.

Return procedure for L7981A:

1.Submit a request within 90 days.

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

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