onsemi FSB649

Overview

FSB649 from ON Semiconductor is an NPN low-saturation transistor in SuperSOT™-3 package, rated for 3 A continuous collector current, 25 V V_CEO, and 300 mV V_CE(sat) at I_C = 1 A / I_B = 100 mA. It delivers high DC current gain (h_FE ≥ 70 at I_C = 1 A) and operates across –55°C to +150°C junction temperature range, used in compact DC-DC converter switching stages.

For engineers reviewing the FSB649 datasheet, pinout, applications, or equivalent options, key selection criteria include verified V_CE(sat) ≤ 600 mV at 3 A, thermal resistance R_θJA = 250°C/W, BVCBO = 35 V, and SuperSOT™-3 footprint compatibility with space-constrained power switch designs.

Technical Context

The FSB649 is a discrete silicon NPN bipolar junction transistor optimized for low-voltage, medium-current switching. Its process (NC) enables low V_BE(sat) = 1.25 V and V_CE(sat) as low as 300 mV at I_C = 1 A / I_B = 100 mA, supporting efficient saturation-mode operation in linear-regulator pass elements and synchronous rectifier drivers.

It features BVCBO = 35 V and BVCEO = 25 V, with f_T = 150 MHz at I_C = 100 mA / V_CE = 5 V, confirming suitability for high-speed switching up to several MHz-within limits set by its 250°C/W junction-to-ambient thermal resistance and 500 mW total dissipation rating.

Key Specifications

Pinout & Package

FSB649 is housed in SuperSOT™-3 package - a surface-mount, 3-pin, plastic-encapsulated outline with exposed emitter pad for thermal enhancement. Dimensions: 2.9 mm × 1.3 mm × 0.9 mm (L × W × H), lead pitch 0.95 mm.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN low-saturation transistor applications.

Compared with FSB649, NSS60201LT1G offers superior saturation voltage and thermal efficiency for 1 A applications, while DXT601100000000000 trades current capability and thermal margin for smaller size-neither is pin-compatible, requiring layout revision.

Availability

FSB649 is available at Aetrix Electronics and suitable for DC-DC converters, linear regulator pass elements, automotive body electronics, and industrial solenoid interfaces requiring stable component supply despite end-of-life status.

Supply support for FSB649 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

ON Semiconductor is a global semiconductor supplier focused on energy-efficient electronics, delivering power management, analog, sensor, and logic solutions for automotive, industrial, and cloud infrastructure markets.

The FSB649 belongs to ON Semiconductor's legacy discrete transistor portfolio designed for cost-sensitive, medium-current switching applications where low saturation voltage and robust thermal behavior are prioritized over ultra-high speed or digital integration.

FAQ

Is FSB649 still in active production?

No, the FSB649 is officially discontinued per ON Semiconductor documentation. It is labeled "DISCONTINUED" in its datasheet with a directive to contact ON Semiconductor representatives for alternatives. Aetrix Electronics maintains limited legacy stock and supports continuity programs for existing designs relying on FSB649, but no new manufacturing runs are planned.

What is the maximum continuous collector current rating for FSB649?

The FSB649 is rated for 3 A continuous collector current (I_C) at T_A = 25°C, as specified in its Absolute Maximum Ratings table. This rating assumes proper PCB thermal design-specifically, soldering the exposed emitter pad to ≥100 mm² of 2-oz copper-to maintain junction temperature ≤150°C under sustained load.

Does FSB649 have a built-in flyback diode?

No, the FSB649 is a bare NPN bipolar transistor with no integrated flyback or clamp diode. When used to switch inductive loads such as solenoids or relays, an external freewheeling diode (e.g., 1N4007 or faster Schottky) must be connected across the load to suppress inductive kickback and prevent junction breakdown.

What is the base-emitter saturation voltage V_BE(sat) of FSB649?

The FSB649 has a base-emitter saturation voltage V_BE(sat) of 1.25 V at I_C = 1 A and I_B = 100 mA, as confirmed in its Small Signal Characteristics table. This value is critical for calculating base resistor values in fixed-bias configurations and confirms sufficient forward bias for reliable saturation under nominal drive conditions.

Can FSB649 replace a standard 2N2222 in high-current applications?

No-while both are NPN transistors, the FSB649 is rated for 3 A continuous collector current and optimized for low-saturation switching, whereas the 2N2222 is typically rated for ≤800 mA and exhibits much higher V_CE(sat). Substituting FSB649 for 2N2222 requires verifying PCB thermal design, base drive capability, and package compatibility (SuperSOT™-3 vs. TO-92), and is not a drop-in replacement.