onsemi FAN2508SX

Overview

FAN2508SX from Fairchild Semiconductor is an adjustable-output CMOS low-dropout (LDO) voltage regulator in SOT-23-5 package, delivering up to 50 mA with 50 mV dropout at full load, 25 µA ground current at 50 mA, and enable/shutdown control. It operates from 2.7 V to 6.5 V input and supports output voltage adjustment via external resistor divider, targeting power management in space-constrained portable electronics.

For engineers reviewing the FAN2508SX datasheet, pinout, applications, or equivalent options, key selection criteria include its ADJ-pin configuration for programmable output, ultra-low quiescent current under load, thermal shutdown protection, and compatibility with low-ESR ceramic output capacitors down to 1 µF.

Technical Context

The FAN2508SX uses a P-channel MOSFET series pass element with ~1 Ω on-resistance, enabling low dropout performance superior to bipolar LDOs. Its error amplifier compares feedback from the ADJ pin against a 1.32 V (typ) bandgap reference to regulate output voltage.

Loop stability is maintained across wide ESR ranges (10 mΩ to 10 Ω) in output capacitors, and internal thermal limiting disables output above 150 °C junction temperature. Enable control reduces ground current to <1 µA in shutdown mode.

Key Specifications

Pinout & Package

SOT-23-5 surface-mount package with 1.3 mm × 2.9 mm footprint and 1.1 mm height; optimized for thermal dissipation on PCB copper areas.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MCP1702T-3302E/MB and TLC7701IPW, the FAN2508SX uniquely balances adjustability, ultra-low dropout (50 mV), and micropower operation (25 µA) in a 5-pin SOT-23 package-making it optimal for battery-powered designs requiring flexible, efficient, and space-constrained voltage regulation.

Availability

FAN2508SX is available at Aetrix Electronics and suitable for cellular handsets, portable cameras, laptop subsystems, and PDA power management requiring stable component supply across high-mix, low-volume production runs.

Supply support for FAN2508SX 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 analog and power IC manufacturer acquired by ON Semiconductor in 2016; known for high-performance, cost-optimized solutions in portable and power management markets.

The FAN2508/FAN2509 family was designed specifically for GSM/TDMA handsets, laptops, and other battery-powered portable devices-emphasizing micropower efficiency, low dropout, and compact packaging.

FAQ

What output voltage range does the FAN2508SX support?

The FAN2508SX supports an adjustable output voltage range from 1.8 V up to approximately VIN minus dropout voltage (e.g., ~5.95 V at VIN = 6.5 V). This is achieved using an external resistor divider connected to the ADJ pin, referenced to the internal 1.32 V bandgap. The FAN2508SX datasheet specifies that V_OUT = 1.32 V × (1 + R_upper/R_lower), with total divider resistance ≤250 kΩ to maintain bias under no-load conditions.

How does the enable functionality work on the FAN2508SX?

The EN pin on the FAN2508SX is an active-high digital input: applying ≥2.0 V enables the regulator output, while ≤0.4 V forces shutdown with ground current reduced to <1 µA. Leaving the pin floating causes erratic operation, so it must be tied to VIN if unused. The FAN2508SX enable response time is 500 µs, allowing fast power sequencing in portable systems.

Can the FAN2508SX operate with a 1 µF ceramic output capacitor?

Yes-the FAN2508SX is explicitly designed for stable operation with 1 µF or larger ceramic, tantalum, or aluminum electrolytic output capacitors across a wide ESR range (10 mΩ to 10 Ω). Unlike many older LDOs, its loop compensation is insensitive to capacitor ESR, eliminating the need for precise ESR matching. A 1 µF X7R ceramic capacitor placed close to the VOUT and GND pins ensures optimal noise and transient performance for the FAN2508SX.

What is the maximum junction temperature and thermal protection behavior of the FAN2508SX?

The FAN2508SX features thermal shutdown at 150 °C junction temperature. When exceeded, the output is disabled until the die cools below the threshold, then automatically re-enables. Its maximum rated junction temperature is 125 °C for continuous operation. Thermal resistance θ_JA depends on PCB layout: ~235 °C/W for minimum copper, improving to ~130 °C/W with 4 in² of backside copper. This behavior is fully documented in the FAN2508SX datasheet's Thermal Characteristics section.

Is the FAN2508SX pin-compatible with other members of the FAN2508/FAN2509 family?

No-the FAN2508SX is not pin-compatible with fixed-output FAN2508-XX or FAN2509-XX variants due to functional differences at pin 4: FAN2508SX uses ADJ, while FAN2508S25X uses BYP and FAN2509S25X uses ERR. Though all share the same SOT-23-5 package and identical pin 1–3, 5 assignments, swapping them requires PCB redesign. The FAN2508SX pinout is unique to the adjustable version and must be verified against the official FAN2508SX datasheet.