RS31309 - Simple 2.97V-18V 4A eFuse Protection Switch

RS31309 Wide-Input 18V, 4A eFuse for Intelligent Power Rail Protection

Modern electronic systems often require protection across multiple supply rails, from low-voltage digital logic to intermediate power buses. This is a versatile wide-input eFuse that provides intelligent circuit protection for power rails ranging from 2.97V to 18V, eliminating the need for multiple voltage-specific protection devices.

Designed for distributed power architectures, the RS31309 integrates a low 34mΩ pass MOSFET, adjustable 0.5A to 4A current limiting, programmable output slew rate, adjustable input undervoltage lockout (UVLO), and comprehensive fault protection into a compact 2 × 2 mm WSON-8 package. Whether protecting 3.3V, 5V, 9V, 12V, or other intermediate supply rails, the RS31309 provides a flexible, highly integrated solution that simplifies system design while improving reliability.

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One Device for Multiple Power Rails

Unlike fixed-voltage eFuses that are optimized for a single supply rail, the RS31309 supports an exceptionally wide 2.97V to 18V operating range, making it ideal for systems with multiple voltage domains.

A single device can protect:

• 3.3V digital rails
• 5V peripheral supplies
• 9V industrial rails
• 12V distributed power buses
• Intermediate power rails up to 18V

This flexibility reduces inventory, simplifies qualification, and allows designers to standardize on a common protection architecture across multiple products.

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Comprehensive Circuit Protection

The eFuse continuously monitors system conditions and protects downstream circuitry against electrical faults before damage can occur.

Integrated protection features include:

• Adjustable 0.5A to 4A current limit
• Programmable input UVLO
• Adjustable output slew rate
• Overtemperature protection
• Fast short-circuit protection
• Reverse current blocking
• Logic enable input for power sequencing

Together, these integrated functions improve overall system reliability while reducing external component count.

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Efficient Power Delivery

The integrated 34mΩ power MOSFET minimizes voltage drop and conduction losses while eliminating the need for an external pass transistor.

Benefits include:

• Lower power dissipation
• Reduced heat generation
• Higher system efficiency
• Smaller PCB footprint
• Simplified PCB layout

The highly integrated design helps engineers reduce BOM cost while improving overall power system performance.

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Controlled Startup and Inrush Current Management

Large capacitive loads can generate substantial inrush current during startup. The RS31309 provides programmable output slew-rate control using a single external capacitor connected to the dV/dt pin, allowing designers to tailor startup performance to their application.

Combined with adjustable current limiting and UVLO, the device enables:

• Controlled startup
• Reduced inrush current
• Improved hot-plug reliability
• Protection of upstream power supplies
• Reliable power sequencing

These capabilities make the RS31309 particularly well suited for industrial equipment, embedded computing, networking systems, and modular electronics.

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Flexible Fault Response

Different applications require different recovery behavior following a fault. The RS31309 family offers multiple protection options, allowing designers to select the operating mode that best matches system requirements.

Available options include:

• RS31309A – Latch-off protection
• RS31309B – Auto-retry protection
• RS31309D – Auto-retry with Quick Output Discharge (QOD)

This flexibility allows the same device family to support applications ranging from industrial control systems to communications infrastructure.

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Typical Applications

The RS31309 is ideal for protecting:

• Industrial automation equipment
• Embedded computing platforms
• Networking equipment
• Communications systems
• Storage systems
• FPGA and processor power rails
• Adapter-powered electronics
• General-purpose distributed power rails
• Multi-voltage power architectures

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Part of Reed Semiconductor’s Compact eFuse Family

The RS31309 complements Reed Semiconductor’s family of compact eFuses, providing a flexible solution when a single device must support multiple supply voltages.

For designs with well-defined supply voltages, the voltage-specific devices provide optimized protection. For platforms requiring flexibility across multiple rails, the RS31309 offers a single solution that simplifies design and inventory management.

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Why Choose the RS31309?

The RS31309 combines wide-input operation, programmable protection, and low-loss power delivery into a compact eFuse optimized for today’s multi-voltage systems. Supporting input voltages from 2.97V to 18V, it protects a wide range of power rails with a single device, helping engineers reduce BOM complexity while improving system reliability.