onsemi FUSB251UCX

Overview

FUSB251UCX from onsemi is an I²C-controlled USB Type-C CC and SBU protection IC with integrated overvoltage protection, moisture detection, dead battery mode (R_d = 5.1 kΩ), ±35 V surge tolerance, and 24 V DC pin tolerance on CC/SBU lines. It implements SPST switches for CC1/CC2 and SBU1/SBU2 paths, enabling safe, intelligent USB-C port management in portable consumer devices.

For engineers reviewing the FUSB251UCX datasheet, pinout, applications, or equivalent options, this device delivers verified moisture-aware port protection, programmable OVP thresholds (CC: 5.85 V typ, SBU: 4.5 V typ), I²C register-based switch control, and interrupt-driven event notification - critical for robust USB-C implementation in smartphones, tablets, and automotive accessories.

Technical Context

The FUSB251UCX integrates dual independent protection domains: CC path (for USB PD communication and VCONN delivery) and SBU path (for DisplayPort Alt Mode or UART), each with dedicated OVP circuitry, 0.3 Ω / 3 Ω typical R_ON, and automatic switch closure upon valid VDD (2.7–5.5 V). Its moisture detection uses ADC-based resistance measurement on CC/SBU pins with configurable thresholds and dry-check validation.

It features a full I²C slave interface compliant with Fast Mode (400 kHz), open-drain INTB output with register-mapped interrupt sources (OVP, moisture, timer expiry), factory test mode via FM pin, and on-chip IEC 61000-4-2 ESD protection supported by external CAP pin capacitor (0.1–1.0 µF).

Key Specifications

Pinout & Package

Package: WLCSP-15 (Case 567WV), 1.49 mm × 2.06 mm × 0.574 mm, 3×5 ball array, bottom-side solder terminals.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar USB-C CC/SBU protection applications.

Compared with TUSB546A and STUSB4500, the FUSB251UCX uniquely combines CC/SBU overvoltage protection, programmable moisture detection, and dead-battery Rd mode in a single WLCSP-15 package - making it the only solution optimized for safety-critical, space-constrained USB-C endpoints where environmental resilience is mandatory.

Availability

FUSB251UCX is available at Aetrix Electronics and suitable for smartphone, tablet, and automotive USB-C accessory designs requiring stable component supply, long-term lifecycle support, and traceable sourcing for production ramp.

Supply support for FUSB251UCX 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

onsemi is a global semiconductor leader delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The FUSB251UCX belongs to onsemi's USB Type-C Protection IC product line, engineered specifically to address moisture, overvoltage, and dead-battery challenges in consumer and automotive USB-C endpoints - not as a general-purpose switch or controller.

FAQ

What is the primary function of the FUSB251UCX in a USB-C design?

The FUSB251UCX serves as an intelligent front-end protection IC for USB-C ports, providing overvoltage protection on CC and SBU lines, moisture detection via ADC-based resistance measurement, dead-battery Rd pull-down (5.1 kΩ), and I²C-controllable SPST switching. It ensures safe, reliable USB-C connectivity in smartphones, tablets, and automotive accessories where environmental resilience is critical. The FUSB251UCX operates independently of the Type-C controller, enhancing system robustness without adding firmware complexity.

Does the FUSB251UCX support both CC and SBU protection simultaneously?

Yes, the FUSB251UCX provides fully independent protection for both CC and SBU paths: CC1/CC2 switches include 5.85 V typical OVP and 24 V DC tolerance, while SBU1/SBU2 switches feature 4.5 V typical OVP and identical 24 V tolerance. Each domain has dedicated OVP circuitry, moisture detection capability, and interrupt reporting (via separate bits in the INTB register), allowing simultaneous monitoring and isolated response - for example, opening only the CC path during a CC overvoltage event while keeping SBU active for DP Alt Mode.

How does the FUSB251UCX handle moisture detection, and what design actions does it enable?

The FUSB251UCX performs moisture detection by applying a 1 V source with 320 kΩ pull-up to CC or SBU pins and measuring resulting voltage via integrated ADC to infer leakage resistance (down to 17 kΩ). Upon detection, it asserts INTB and updates the MOISTURE_STATUS register (0x06). This enables host firmware to isolate the port (open CC/SBU switches), log the event, initiate dry-check routines, or trigger UI alerts - preventing electrochemical corrosion before irreversible damage occurs. The FUSB251UCX supports configurable thresholds, dry-check timers, and dual-path (CC → SBU) detection sequencing.

What are the key electrical specifications that define the FUSB251UCX's USB-C port protection capability?

Key specs include ±35 V surge protection on CC/SBU pins, 24 V DC tolerance, 300 mΩ typical CC R_ON (supporting ≤1 A VCONN), 3 Ω typical SBU R_ON (preserving 30 MHz bandwidth), 5.85 V CC OVP threshold, 4.5 V SBU OVP threshold, and 5.1 kΩ dead-battery Rd pull-down. These values ensure compatibility with USB PD 3.0, withstand automotive transients, maintain signal integrity for DP Alt Mode, and guarantee charging initiation even with zero system voltage - all validated per IEC 61000-4-2 and JEDEC ESD standards.

Can the FUSB251UCX be used without an external microcontroller?

No - the FUSB251UCX requires an I²C master (e.g., application processor or MCU) for configuration, interrupt handling, and register access. While it auto-closes CC/SBU switches on valid VDD and provides default Rd in dead-battery mode, core functions like moisture detection enablement, OVP threshold adjustment, manual switch control, and interrupt clearing depend on I²C transactions. The FUSB251UCX has no autonomous decision-making logic beyond POR behavior and OVP response; all advanced protection policies must be implemented in host firmware using its register map (e.g., 0x02 Control, 0x03 Interrupt, 0x06 Moisture Status).