onsemi FAN2503S25X

Overview

FAN2503S25X from Fairchild Semiconductor is a 2.5 V fixed-output, 150 mA CMOS low-dropout (LDO) voltage regulator in SOT-23-5 package, featuring an open-drain ERR flag pin, 150 mV dropout at 150 mA load, 25 µA ground current at full load, and thermal shutdown protection - designed for power management in portable battery-powered systems such as cellular handsets and notebook computers.

For engineers reviewing the FAN2503S25X datasheet, pinout, applications, or equivalent options, key selection criteria include its 2.5 V fixed output with ±2% accuracy, ERR fault-flag functionality, enable-controlled shutdown (<1 µA), ultra-low quiescent current, and compatibility with ceramic output capacitors down to 1 µF.

Technical Context

The FAN2503S25X uses a P-channel MOSFET series pass element with ~1 Ω on-resistance, enabling low dropout performance across temperature and load. Its error amplifier compares V_OUT against a 1.32 V bandgap reference and drives the pass device to maintain regulation.

Pin 4 functions as an open-drain ERR flag indicating output undervoltage (LOW when V_OUT < 95% of nominal); EN (pin 3) provides digital shutdown control; internal thermal limiting disables output above 150°C junction temperature and re-enables upon cooling.

Key Specifications

Pinout & Package

SOT-23-5 surface-mount package (JEDEC SC-74A), 2.9 mm × 1.6 mm × 1.1 mm body, with exposed pad not electrically connected.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar LDO regulator applications.

Compared with FAN2503S25X, MCP1700T-2502E/MB offers lower quiescent current but omits enable and fault flag, while XC6206P252MR-G matches pin count and current rating but lacks the ERR diagnostic output - making FAN2503S25X uniquely suited for applications requiring both low-power operation and real-time output health monitoring.

Availability

FAN2503S25X is available at Aetrix Electronics and suitable for cellular handsets, portable cameras, notebook subsystems, and PDA power management requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for FAN2503S25X 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

Fairchild Semiconductor was a U.S.-based designer of high-performance analog and power ICs, acquired by ON Semiconductor in 2016; its legacy LDO portfolio remains widely deployed in portable electronics.

The FAN2502/FAN2503 family was engineered specifically for cost-sensitive, space-constrained battery-powered devices - emphasizing ultra-low IQ, low dropout, thermal robustness, and flexible pin configurations (ADJ/BYP/ERR) across a single footprint.

FAQ

What is the maximum input voltage rating for the FAN2503S25X?

The FAN2503S25X has an absolute maximum input voltage of 7 V, but its recommended operating range is 2.7 V to 6.5 V. Operation above 6.5 V may compromise reliability or parametric performance, and the device includes internal thermal protection to prevent damage under sustained overvoltage or overload conditions. Always refer to the Absolute Maximum Ratings table in the official FAN2503S25X datasheet for design margining.

Does the FAN2503S25X require an external bypass capacitor?

No, the FAN2503S25X does not use a bypass capacitor - pin 4 is assigned as ERR (error flag), not BYP. The bypass function is exclusive to FAN2502-XX variants. For FAN2503S25X, a 100 kΩ pull-up resistor on the ERR pin is recommended if fault monitoring is used; no capacitor is needed or specified for that pin.

How does the ERR pin on the FAN2503S25X behave during normal operation?

During normal operation, the ERR pin on the FAN2503S25X remains HIGH (open-drain pulled up), indicating V_OUT is within specification (>2.375 V). It goes LOW only when output voltage falls below 95% of nominal (i.e., <2.375 V) due to input dropout, thermal shutdown, or overload. The transition time is typically 3 ms, and the pin requires an external pull-up resistor (100 kΩ recommended) to interface with logic inputs.

Can the FAN2503S25X be used without connecting the EN pin?

No - leaving the EN pin floating will cause erratic operation. If enable functionality is not required, EN must be tied directly to VIN to ensure the FAN2503S25X remains enabled. Connecting EN to GND forces shutdown (<1 µA I_GND). This requirement is explicitly stated in the datasheet to prevent unintended power cycling or instability.

What is the minimum output capacitance required for stability with the FAN2503S25X?

The FAN2503S25X requires a minimum 1 µF ceramic output capacitor for guaranteed loop stability across temperature, load, and process variations. It supports ESR values from 10 mΩ to 10 Ω, making it compatible with X5R/X7R ceramics, tantalum, and aluminum electrolytics - unlike many older LDOs that demand strict ESR ranges.