RS31385 - Stackable 50A eFuse with Analog Current Monitoring (Fixed Latch-Off)

RS31385 4V to 16V, 50A Stackable eFuse with Latch-Off Protection and Current Monitoring

Modern servers, networking equipment, PCIe accelerator cards, and industrial systems require robust circuit protection capable of handling high current while preventing catastrophic failures caused by overloads, short circuits, or overheating. The RS31385 delivers a fully integrated 50A eFuse and hot-swap solution that combines low-loss power switching, precision current monitoring, programmable protection, and scalable operation in a compact 5 × 5 mm LGA package. Designed for applications where safety and fault isolation are critical, the RS31385 features latch-off fault protection, ensuring that severe faults remain isolated until the system is intentionally reset.

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Designed for High-Current Power Rail Protection

Operating from 4V to 16V, the RS31385 integrates a low 0.8mΩ power MOSFET capable of supporting 50A continuous load current, making it well suited for protecting intermediate power rails in servers, storage systems, networking equipment, and PCIe expansion cards.

Typical applications include:

• AI accelerator cards
• Server power distribution
• PCIe and PCI cards
• Enterprise storage
• Networking switches
• Industrial computing
• Hot-plug systems
• Telecom infrastructure

The highly integrated architecture minimizes external components while reducing PCB area and simplifying system design.

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Low-Loss Integrated Power Protection

Unlike discrete hot-swap solutions requiring external MOSFETs, the RS31385 integrates the power MOSFET and protection circuitry into a single device.

Benefits include:

• Reduced BOM cost
• Smaller PCB footprint
• Simplified layout
• Lower conduction losses
• Improved thermal performance
• Faster design cycles

A programmable soft-start capacitor controls output ramp-up, minimizing inrush current during hot-plug events while reducing stress on connectors and power supplies.

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Comprehensive Analog Protection

The RS31385 continuously monitors system conditions and provides multiple layers of protection, including:

• Programmable overcurrent protection
• Fixed 100A fast-trip short-circuit protection
• Input overvoltage protection
• Overtemperature protection
• Input-to-output short-circuit detection
• Fault indication output
• Fault type output

The programmable current limit allows designers to optimize protection for individual power rails while maintaining reliable system operation under dynamic load conditions.

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Latch-Off Protection for Critical Systems

The defining feature of the RS31385 is its latch-off fault response.

When a severe fault occurs, the device immediately disconnects the load and remains off until power is cycled or reset, preventing repeated fault cycling and allowing the root cause to be investigated before power is restored. This behavior is ideal for:

• Enterprise servers
• High-value processor boards
• FPGA platforms
• Industrial control equipment
• Telecom infrastructure
• Mission-critical computing

For applications where automatic recovery is preferred, Reed Semiconductor also offers the RS31387, which provides the same hardware platform with auto-retry fault recovery instead of latch-off.

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Accurate Current Monitoring

Integrated current sensing provides an analog current monitor output (IMON), allowing the host system to monitor load current without requiring external shunt resistors or dedicated current-sense amplifiers.

This enables:

• System health monitoring
• Load profiling
• Power optimization
• Fault diagnostics
• Predictive maintenance

The analog interface makes integration straightforward for systems that do not require digital PMBus telemetry.

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Scalable for Higher Power Designs

The RS31385 is designed to operate as either a standalone 50A protection device or as part of a parallel architecture for significantly higher current applications.

Multiple RS31385 devices can be connected in parallel to increase available output current while maintaining synchronized protection and current sharing. This scalable architecture allows designers to support a wide range of system power requirements using a common hardware platform, simplifying qualification and reducing design complexity.

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Migration Path to Digital Power Management

For systems requiring digital configuration, telemetry, and PMBus communication, Reed Semiconductor also offers the RS31380.

The RS31380 builds on the same high-current integrated protection concept by adding:

• PMBus® 1.3 digital interface
• Remote configuration
• Real-time voltage, current, power, and temperature telemetry
• Fault logging
• Digital monitoring and diagnostics

While the RS31385 and RS31380 use different pinouts and are not pin-compatible, they target similar high-current applications and provide a natural migration path from analog protection to intelligent digital power management as system requirements evolve.

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Why Choose the RS31385?

The RS31385 combines a 50A integrated eFuse, 0.8mΩ power MOSFET, programmable analog protection, accurate current monitoring, and parallel scalability into a compact 5 × 5 mm package. Its latch-off fault response makes it ideal for mission-critical systems where faults must be isolated until corrective action is taken, while support for parallel operation enables designers to scale seamlessly from 50A to substantially higher current levels. For applications requiring intelligent telemetry and PMBus control, the RS31380 provides a complementary digital solution built for the same class of high-current power systems.