Send an Inquiry

To receive a quote for your project, please fill in the following information, and we’ll get back to you promptly.

Submit Inventory List

Please fill in the following information, and we’ll get back to you promptly.

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

STMicroelectronics L7981TR

Name: L7981TR
Brand: STMicroelectronics
SKU: L7981TR
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

Compare

Part No.:: L7981TR

Manufacturer:: STMicroelectronics

Category:: Voltage Regulators - DC DC Switching Regulators

Package:: 8-VFDFN Exposed Pad

Datasheet:: L7981TR.pdf

Description:: IC REG BUCK ADJ 3A 8VFQFPN

Quantity:: RFQ Add To RFQ list

Payment:

Shipping:

Inventory:2,359

Please send an inquiry. Send us your inquiry, and we will respond immediately.

Product details

Overview

L7981TR from STMicroelectronics is a 3 A synchronous step-down switching regulator with integrated P-channel MOSFET, designed for high-efficiency DC-DC conversion in space-constrained power rails. 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 100% duty cycle for low-dropout operation - used in FPGA core supplies and LCD TV main power rails.

For engineers reviewing the L7981TR datasheet, L7981TR pinout, L7981TR application, or L7981TR equivalent, key selection criteria include verified thermal resistance (HSOP8: 40°C/W), confirmed current limit (3.7 A min), validated voltage feed-forward architecture, and real-world enable threshold (1.2 V ON / 0.3 V OFF) - all critical for industrial and consumer DC-DC module design.

Technical Context

The L7981TR implements voltage-mode PWM control with a fixed-frequency sawtooth oscillator whose slope is dynamically adjusted via voltage feed-forward (input-dependent ramp scaling) and frequency feed-forward (FSW-resistor–dependent ramp scaling) to maintain constant loop gain across line and frequency variations. Its error amplifier features 100 dB DC gain, 4.5 MHz GBWP, and rail-to-rail output swing (0–3.3 V).

Synchronization is implemented via the SYNCH pin: when left floating, it outputs a 180° phase-shifted clock; when tied to an external master clock >250 kHz, it locks with zero phase shift. Overcurrent protection uses blanking time (~200 ns) and dual-mode response - hiccup mode under regulation, pulse-skipping constant-current mode during soft-start.

Key Specifications

Parameter	Value and Actual Design Meaning
Output current	3 A continuous load capability with 3.7 A minimum current limit - enables robust 5 V/3 A or 1.2 V/3 A FPGA core rails.
Input voltage range	4.5 V to 28 V - supports wide-input industrial 12/24 V bus and automotive battery-supplied systems.
Output voltage adjust	0.6 V to VIN - allows precise low-voltage core supplies (e.g., 0.85 V for modern SoCs) using external resistor divider.
Switching frequency	250 kHz (default) to 1 MHz (via FSW resistor) - balances EMI, efficiency, and inductor size for compact designs.
Thermal resistance	HSOP8: 40°C/W - enables 3 A operation at TA ≤ 85°C without forced air, verified on demo board.
Enable threshold	1.2 V (ON), 0.3 V (OFF) - compatible with standard logic-level microcontrollers and sequencers.
Feedback reference	0.6 V ±7 mV (0.593–0.607 V) - ensures tight output regulation accuracy across temperature and load.

Pinout & Package

Available in HSOP8 package with exposed thermal pad (R_thJA = 40°C/W) and VFQFPN 3×3–8L (R_thJA = 60°C/W). Pinout defined per STMicroelectronics DocID15182 Rev 5, Figure 2 and Table 1.

Pin/Terminal	Circuit Role	Design Meaning
OUT	Regulator output	High-current power node connected directly to inductor and output capacitor - requires low-inductance layout.
SYNCH	Master/slave sync I/O	Configurable as output (180° phase-shifted clock) or input (external sync signal); enables multi-phase interleaving.
EN	Enable control input	Active-high logic interface with internal pull-down - simplifies power sequencing without external bias.
COMP	Error amplifier output	Direct access to EA output for Type II/III compensation network - sets loop stability and transient response.
FB	Feedback input	Connects to resistor divider from V_OUT; internal 0.6 V reference enables precise output voltage setting.
FSW	Frequency set input	Resistor-to-ground sets switching frequency from 250 kHz to 1 MHz - adjusts ripple, efficiency, and EMI profile.
GND	Power and signal ground	Common return for power stage, control circuitry, and thermal pad - must be low-impedance plane.
VCC	Unregulated input supply	Bias rail for internal circuitry; requires local 100 nF–1 µF ceramic bypass near pin to suppress noise.

Key Features

Feature	Design Value
Voltage feed-forward	Adjusts sawtooth slope with input voltage to maintain constant PWM gain - improves line transient response by >40% vs. non-feed-forward buck controllers.
Zero-load operation	Stable regulation at 0 A output current - eliminates need for dummy loads in always-on standby circuits.
Hiccup overcurrent	Auto-retry shutdown with 2048-clock-cycle off-time - protects against sustained short-circuit while enabling self-recovery.
Thermal shutdown	Hysteretic trip at 150°C (on) / 130°C (off) - prevents thermal runaway with fast localized sensing near P-MOSFET junction.
Internal soft-start	64-step staircase ramp (9.5 mV/step) synchronized to switching clock - ensures monotonic V_OUT rise and limits inrush to <1.5× I_OUT.

Applications

FPGA Core Supply

LCD TV Main Rail

Use Scenario: Powering Xilinx Artix-7 or Intel Cyclone V FPGA core logic requiring stable 1.0 V @ 2.5 A with <±1% tolerance.

IC Role / Device Role / Timing Role: Primary DC-DC converter delivering regulated core voltage; operates at 500 kHz to minimize inductor size while meeting EMI Class B limits.

Use Value: Integrated 3.7 A current limit and 0.6 V reference ensure accurate core voltage under dynamic load steps up to 2 A/µs.

Use Scenario: Generating 12 V @ 2 A for LCD panel backlight drivers and TCON logic in 32-inch consumer TVs.

IC Role / Device Role / Timing Role: High-current buck regulator replacing discrete controller + MOSFET solution; configured for 250 kHz to reduce audible noise.

Use Value: 100% duty cycle capability maintains regulation during brown-out events down to 4.5 V input - critical for AC-DC adapter dropout resilience.

Industrial PLC I/O Module

DSL Modem Power Tree

Use Scenario: Providing isolated 3.3 V @ 1.2 A for digital I/O conditioning and communication interfaces in DIN-rail mounted PLCs.

IC Role / Device Role / Timing Role: Secondary-side buck regulator fed from isolated 12 V intermediate bus; enabled via microcontroller GPIO.

Use Value: EN pin logic compatibility (1.2 V threshold) and <30 µA standby current enable low-power sleep modes compliant with IEC 61131-2.

Use Scenario: Generating 5 V @ 1.5 A and 3.3 V @ 1 A from shared 12 V input in xDSL modems with strict thermal envelope.

IC Role / Device Role / Timing Role: Dual-rail power source where L7981TR supplies 5 V and cascades to LDO for 3.3 V - synchronized via SYNCH pin.

Use Value: Phase-shifted synchronization reduces input capacitor RMS current by 30%, allowing smaller 10 µF X7R ceramics instead of 22 µF tantalum.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
LM2678SD-ADJ/NOPB	5 A rated, 260 kHz fixed frequency, no frequency programming or SYNCH pin	Lacks voltage feed-forward and sync capability - less suitable for multi-phase or line-sensitive applications	Choose for higher current headroom where sync and feed-forward are unnecessary
TPS54332DR	3 A, 1 MHz max, integrated N-MOSFET, requires external bootstrap capacitor	Different topology (N-ch high-side) increases BOM count and layout complexity vs. L7981TR's P-ch integrated solution	Prefer when 1 MHz switching is mandatory and bootstrap routing is acceptable

Compared with LM2678SD-ADJ/NOPB and TPS54332DR, the L7981TR uniquely combines P-MOSFET integration (no bootstrap), voltage/frequency feed-forward (superior line regulation), and SYNC-capable multi-phase support - making it optimal for thermally constrained, high-transient consumer and industrial DC-DC modules.

Availability

L7981TR is available at Aetrix Electronics and suitable for FPGA core supplies, LCD TV main rails, industrial PLC I/O modules, and DSL modem power trees requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for L7981TR 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, MCU, power, and sensor solutions for automotive, industrial, and consumer markets.

The L7981TR belongs to ST's high-current monolithic buck regulator product line, engineered for space-efficient, thermally robust DC-DC conversion in cost-sensitive industrial and consumer power systems.

FAQ

What is the maximum allowable input voltage for continuous operation?

The L7981TR supports continuous operation up to 28 V input, with absolute maximum rating of 30 V. Operation above 28 V risks exceeding internal UVLO hysteresis and may trigger thermal shutdown due to increased conduction losses in the integrated P-MOSFET. Designers must ensure input transient clamping (e.g., TVS) if system-level surges exceed 28 V.

Can the L7981TR operate in 100% duty cycle mode, and what conditions enable it?

Yes - the L7981TR supports true 100% duty cycle operation when the feedback voltage falls below 0.6 V, allowing V_OUT to track V_IN minus small dropouts. This occurs during low-V_IN/high-V_OUT conditions (e.g., 5 V input → 4.8 V output) and is enabled by internal circuitry that disables PWM modulation while maintaining gate drive to the P-MOSFET.

How does the SYNCH pin behave when two L7981TR devices are interconnected?

When SYNCH pins of two L7981TRs are tied together, the device with higher oscillator frequency becomes the master and the other synchronizes as slave with 180° phase shift. This interleaving reduces input capacitor RMS current by ~30% and eases thermal management - confirmed in ST application note AN4405 for multi-phase buck designs.

What is the purpose of the COMP pin, and how is it used in loop compensation?

COMP is the error amplifier output, providing direct access to the transconductance amplifier node for external Type II or Type III compensation networks. It sources up to 17 mA and sinks up to 25 mA, enabling robust pole-zero placement to stabilize the voltage-mode control loop - especially critical when using low-ESR ceramic output capacitors.

L7981TR Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 8-VFDFN Exposed Pad

Packaging:: Tape & Reel (TR)

Product Status:: Active

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-VFQFPN (3x3)

L7981TR FAQ

1.How can I place an order for L7981TR through Aetrix?

Please submit a Request for Quotation (RFQ) for L7981TR 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 L7981TR reliable?

The price and inventory of L7981TR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L7981TR is usually 5 days.

3.What payment methods are accepted for L7981TR?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L7981TR transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L7981TR?

L7981TR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L7981TR 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 L7981TR?

For technical support, including L7981TR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L7981TR requirements.

6.How does Aetrix verify that L7981TR is sourced from the original manufacturer or authorized distributors?

All L7981TR 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 L7981TR meets industry standards.

7.What is the process for return or replacement of L7981TR?

All L7981TR units undergo pre-shipment inspection (PSI). If there is an issue with L7981TR, 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 L7981TR part is unused and in its original packaging.

Return procedure for L7981TR:

1.Submit a request within 90 days.

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

Tech Hub

2026-09-03 Logic Level Shifter: How to Connect 3.3V and 5V Logic Safely

A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.

2026-09-03 74HC595 vs TPIC6B595: Output Drive, Pinout, Current, and Load Selection

The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…

2026-09-01 74HC595 Pinout, Timing, Output Current, and Applications

The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…

2026-09-01 Latch vs Flip-Flop: Timing, Differences and Design Choices

A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…

2026-08-30 D Latch Circuit: Truth Table, Timing, ICs and Applications

A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …

2026-08-28 SR Latch Explained: NOR and NAND Circuits, Truth Tables, and Applications

An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…

2026-08-27 Latch Circuit: SR and D Latches, Truth Tables, Timing, and Applications

Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…

2026-08-21 What Is an LED Driver? Types, Circuits, Dimming, and Selection

An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…

2026-08-18 Operational Amplifier (Op Amp): Basics, Configurations, Feedback and Applications

Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…

2026-08-14 Jumper Cables: How to Use, Connect and Choose Them Safely

Jumper cables guide covering safe connection order, red and black clamp placement, final ground connection, cable gauge, length, clamp quality, copper vs CCA cables, jump starter comparison and battery…