L7981TR - 2A Step-Down Switching Regulator | STMicroelectronics
MPN: L7981TR β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.25 | $1.25 |
| 10 | $1.12 | $11.20 |
| 100 | $0.98 | $98.00 |
| 500 | $0.85 | $425.00 |
| 1,000 | $0.75 | $750.00 |
Drop-in alternatives for L7981TR β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
L7981
β Drop-Inπ Reference alternative (not in catalog)
L7986TR
β Drop-Inβ 99,999 In Stock
$1.85 / Unit
View Datasheet βL7987TR
β Drop-Inπ Reference alternative (not in catalog)
LM2596S-3.3
β Drop-Inπ Reference alternative (not in catalog)
MP1584EN
β Drop-Inπ Reference alternative (not in catalog)
L7981TR Maximum Ratings & Electrical Characteristics
| Output Type | Fixed |
| Output Voltage | 3.3 V |
| Maximum Output Current | 2 A |
| Input Voltage Range | 4.5 V to 28 V |
| Switching Frequency | 250 kHz |
| Efficiency | 85% (typical, 12V to 3.3V at 1A) |
| Quiescent Current | 2.5 mA |
| Thermal Resistance | 62.5 C/W |
| Operating Temperature | -40C to +150C |
| Package | SO-8 |
| Mounting Type | Surface Mount |
| MSL Level | 1 (unlimited) |
| RoHS Status | Compliant |
| Enable Pin | Yes (active-high) |
| Synchronous Rectification | No |
L7981TR Pin Configuration
| Pin 1 | BOOT β Bootstrap capacitor connection for high-side driver |
| Pin 2 | IN β Input supply voltage |
| Pin 3 | SW β Switch node output |
| Pin 4 | GND β Ground |
| Pin 5 | FB β Feedback pin (fixed 3.3V output, connect to output) |
| Pin 6 | EN β Enable pin (active high) |
| Pin 7 | COMP β Compensation pin (internal compensation, connect to GND) |
| Pin 8 | VCC β Internal supply voltage (decouple with 1uF capacitor) |
Safe Operating Area (SOA) & Thermal Characteristics
No official SOA curve available for this component. Always operate within absolute maximum ratings specified in the datasheet. Ensure adequate cooling and derate as needed.
Typical Applications
L7981TR is suitable for 6 applications: Point-of-Load (POL) Converters, Industrial Control Systems, Distributed Power Architectures, Battery-Powered Devices, Telecom and Networking Equipment, Consumer Electronics.
Point-of-Load (POL) Converters
The L7981TR is ideal for POL converters that step down a 12V or 24V bus to a 3.3V logic rail. Its 2A output current and high efficiency (85% typical) ensure reliable power delivery to microcontrollers, FPGAs, and DSPs. The fixed 3.3V output simplifies design, while the enable pin allows sequenced power-up in multi-rail systems. The wide input range (4.5V to 28V) accommodates various bus voltages, and the internal compensation reduces external component count, saving board space. In a typical POL application, the L7981TR is placed close to the load, with a 10uF input capacitor and a 22uF output capacitor to minimize ripple. The device's current-mode control provides fast transient response, essential for digital loads that draw dynamic currents. Compared to linear regulators, the switching topology dissipates less power, making it suitable for high-current, high-voltage-drop applications.
Recommended
Industrial Control Systems
In industrial control systems, the L7981TR provides a stable 3.3V rail for sensors, actuators, and communication interfaces. Its wide input voltage range (4.5V to 28V) allows direct connection to 24V industrial buses, eliminating the need for intermediate conversion stages. The device's thermal shutdown and current limiting protect against overloads, enhancing system reliability. The SO-8 package with a thermal resistance of 62.5 C/W can handle moderate power dissipation without external heatsinking, making it suitable for enclosed control cabinets. The enable pin enables power sequencing in systems with multiple voltage rails, ensuring proper startup order. The high efficiency reduces heat generation, which is critical in sealed enclosures. In a typical industrial application, the L7981TR is used to power a PLC's I/O modules, with input filtering to handle transients from inductive loads.
Recommended
Distributed Power Architectures
The L7981TR is well-suited for distributed power architectures where a central power supply generates an intermediate bus voltage (e.g., 12V) that is then converted to local rails. Its 2A output current and high efficiency make it an excellent choice for intermediate bus converters (IBCs) that feed multiple point-of-load regulators. The fixed 3.3V output is a common logic voltage, and the device's small SO-8 package allows dense board layouts. The wide input range ensures compatibility with various bus voltages, and the internal compensation simplifies design. In a distributed power system, the L7981TR can be used to generate a 3.3V rail for digital logic, while other converters handle 5V and 1.8V rails. The enable pin allows coordinated startup, preventing inrush current issues. The device's current-mode control provides good line and load regulation, essential for maintaining stable voltages across the system.
Recommended
Battery-Powered Devices
The L7981TR is an excellent choice for battery-powered devices that require efficient step-down conversion from a battery voltage (e.g., 12V Li-ion pack) to a 3.3V logic rail. Its high efficiency (85% typical) extends battery life, and the low quiescent current of 2.5 mA minimizes standby power consumption. The wide input voltage range accommodates battery voltage variations during discharge. The enable pin allows the device to be shut down when the system is idle, further conserving power. In a typical battery-powered application, the L7981TR is used to power a microcontroller and sensors, with a low-dropout regulator (LDO) for analog circuits that require ultra-low noise. The switching regulator's efficiency reduces heat generation, which is important in portable devices with limited thermal dissipation. The SO-8 package is compact, fitting into space-constrained designs.
Recommended
Telecom and Networking Equipment
In telecom and networking equipment, the L7981TR provides a reliable 3.3V rail for line cards, switches, and routers. Its wide input range (4.5V to 28V) allows operation from standard telecom voltages like -48V (with appropriate front-end conversion) or 12V intermediate rails. The device's high efficiency reduces power dissipation, which is critical in densely packed equipment racks. The enable pin enables power sequencing in systems with multiple voltage rails, ensuring proper startup order. The internal compensation simplifies design, and the SO-8 package is suitable for high-density PCBs. In a typical networking application, the L7981TR powers a switch ASIC and PHY transceivers, with input filtering to meet EMC requirements. The device's current-mode control provides fast transient response, essential for handling bursty network traffic.
Recommended
Consumer Electronics
The L7981TR is used in consumer electronics such as set-top boxes, gaming consoles, and smart home devices to generate a 3.3V rail from a 12V or 5V supply. Its small SO-8 package and high efficiency make it ideal for compact, energy-efficient designs. The fixed 3.3V output is a common logic voltage, and the device's low quiescent current helps meet energy star requirements. The enable pin allows the device to be shut down in standby mode, reducing power consumption. In a typical consumer application, the L7981TR powers a system-on-chip (SoC) and memory, with a 10uH inductor and 22uF output capacitor for stable operation. The device's internal compensation reduces external component count, lowering BOM cost. The wide input range provides design flexibility across different product lines.
Recommended
Recommended Products Summary
Engineering reference data for L7981TR β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | L7981 | L7986TR | L7987TR | LM2596S-3.3 | MP1584EN |
|---|---|---|---|---|---|---|
| Package | SO-8 | SO-8 - same | SO-8 - same | SO-8 - same | SO-8 - same | SO-8 - same |
| Brand | STMicroelectronics | STMicroelectronics | STMicroelectronics | STMicroelectronics | Texas Instruments | Monolithic Power Systems |
| Output Voltage | 3.3V (fixed) | 3.3V (fixed) | 3.3V (fixed) | Adjustable | 3.3V (fixed) | Adjustable |
| Output Current | 2A | 2A | 3A | 2A | 3A | 3A |
| Input Voltage Range | 4.5V to 28V | 4.5V to 28V | 4.5V to 28V | 4.5V to 28V | 4.5V to 40V | 4.5V to 28V |
| Switching Frequency | 250 kHz | 250 kHz | 250 kHz | 250 kHz | 150 kHz | 1.5 MHz |
| Enable Pin | Yes (active-high) | Yes (active-high) | Yes (active-high) | Yes (active-high) | No | Yes (active-high) |
| Internal Compensation | Yes | Yes | Yes | Yes | No | Yes |
Key Differentiators
- Internal compensation simplifies design (vs LM2596S-3.3)
- Enable pin for power sequencing (vs LM2596S-3.3)
- Higher switching frequency reduces component size (vs LM2596S-3.3)
Design Notes
Place the input capacitor (10uF ceramic) as close as possible to the IN pin (pin 2) and GND pin (pin 4) to minimize input ripple and reduce EMI. The output capacitor (22uF ceramic) should be placed near the SW pin (pin 3) and GND. Use a solid ground plane to minimize parasitic inductance. The bootstrap capacitor (100nF) should be connected between BOOT (pin 1) and SW (pin 3) with minimal trace length.
The SO-8 package has a thermal resistance of 62.5 C/W. For a 12V to 3.3V conversion at 2A, power dissipation is approximately (12V - 3.3V) * 2A * (1 - efficiency) = 8.7W * 0.15 = 1.3W, resulting in a temperature rise of 81C above ambient. Ensure adequate copper area on the PCB to dissipate heat, or reduce output current if ambient temperature is high.
Do not exceed the absolute maximum input voltage of 28V. Ensure the enable pin is not left floating; tie it to VIN if not used. The COMP pin (pin 7) should be connected to GND with a small capacitor (e.g., 1nF) for stability, as the device has internal compensation. Use a Schottky diode for the catch diode to minimize switching losses.
Compliance Information
RoHS compliant per STMicroelectronics product page. Not AEC-Q100 qualified. Lead-free finish.
