onsemi FAN1951D25X

Overview

FAN1951D25X from Fairchild Semiconductor is a 2.5V fixed-output, 1.5A low-dropout linear regulator with PNP pass element, 500mV max dropout at 1.5A, logic-level enable input, and open-collector error flag output-designed for post-regulation in 3.0V-to-2.5V conversion in FPGA and DSP power rails.

For engineers reviewing the FAN1951D25X datasheet, pinout, applications, or equivalent options, key selection factors include guaranteed 1.5A output current, thermal shutdown with 150°C trip point, ±2.5% output voltage tolerance over temperature, and compatibility with 10µF low-ESR tantalum output capacitors.

Technical Context

The FAN1951D25X integrates a PNP-based pass transistor enabling low dropout (350mV typical at 1.5A) without requiring external compensation. Its enable pin accepts TTL/CMOS logic levels (V_IH ≥ 2.25V), and its open-collector FLAG pin asserts low during undervoltage or overcurrent events with 93–99.2% V_OUT threshold hysteresis.

It operates across –40°C to +125°C junction temperature with internally limited power dissipation, thermal shutdown hysteresis of 10°C, and ground current as low as 10mA at 750mA load-optimized for stable low-noise regulation in space-constrained digital power domains.

Key Specifications

Pinout & Package

5-Lead TO-252 (DPAK) package with exposed thermal pad (GND-connected TAB); footprint matches JEDEC TO-252 Issue C, Variation AA.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-dropout regulator applications.

Compared with TPS76325QDBVRQ1 and MCP1702T-2502E/MB, the FAN1951D25X uniquely delivers 1.5A output with integrated enable and fault flag in TO-252-making it the sole option among these three for high-current, monitorable 2.5V regulation in dense digital systems.

Availability

FAN1951D25X is available at Aetrix Electronics and suitable for FPGA power delivery, SMPS post-regulation, and cable set-top box SoC core supply requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for FAN1951D25X 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 robust, application-focused power management solutions.

The FAN195x series was designed specifically for low-voltage, high-current digital system regulation-targeting FPGA, DSP, and ASIC core/I/O power domains where dropout, transient response, and fault visibility are critical.

FAQ

What is the maximum input voltage rating for the FAN1951D25X?

The FAN1951D25X has an absolute maximum input voltage of 15V, but its recommended operating supply voltage range is 2.25V to 14V. Operation above 14V risks exceeding thermal limits or violating safe operating area margins-even if within absolute ratings-so 14V is the practical upper limit for continuous use in designs using the FAN1951D25X.

Does the FAN1951D25X require an external output capacitor, and what type is recommended?

Yes, the FAN1951D25X requires a 10µF output capacitor for stability and transient performance. Low-ESR tantalum capacitors are explicitly recommended in the datasheet; ceramic capacitors may cause oscillation due to insufficient ESR. Aluminum electrolytics are acceptable only if ESR remains below 3Ω. This requirement directly impacts reliability of the FAN1951D25X in production systems.

How does the FLAG pin on the FAN1951D25X behave during normal and fault conditions?

The FLAG pin on the FAN1951D25X is an open-collector output that remains high-impedance (floating) during normal operation. It pulls low when output voltage drops below 93% of nominal (2.325V) or current limit is exceeded. Its 400mV max V_OL at 250µA ensures reliable logic-low detection. External pull-up is mandatory-no internal pull-up exists in the FAN1951D25X.

Can the FAN1951D25X be used in place of the FAN1950D25X?

No-the FAN1951D25X is not a drop-in replacement for the FAN1950D25X. While both share the same 2.5V output and TO-252 package, the FAN1951D25X has five pins (including EN and FLAG), whereas the FAN1950D25X has only three pins (IN, OUT, GND). Using the FAN1951D25X in a FAN1950D25X layout would leave EN and FLAG unconnected and potentially floating, risking undefined behavior. The FAN1951D25X requires dedicated PCB routing.

What is the thermal resistance (θ_JA) of the FAN1951D25X in standard PCB mounting?

The datasheet specifies θ_JC = 3°C/W for the TO-252 package, but does not publish θ_JA-which depends entirely on PCB copper area, layer count, and thermal vias. Typical θ_JA for a 1-in² 2-oz copper pad with 6 thermal vias is ~50°C/W. Derating curves in the FAN1951D25X datasheet show output current must be reduced above 85°C ambient-designers must validate thermal performance per their specific layout.