onsemi FZT649

Overview

FZT649 from ON Semiconductor is an NPN low-saturation transistor designed for high-current switching in power management circuits, featuring V_CE(sat) = 300 mV at I_C = 1 A / I_B = 100 mA, h_FE ≥ 70 at I_C = 1 A, and continuous collector current up to 3 A - used in DC-DC converter output stages and motor driver H-bridge legs.

For engineers reviewing the FZT649 datasheet, pinout, applications, or equivalent options, key selection criteria include verified V_CE(sat) performance at 1–3 A load, thermal resistance (R_θJA = 62.5 °C/W), SOT-223 package compatibility, and safe operating area under pulsed conditions per Fairchild/ON Semiconductor documentation.

Technical Context

The FZT649 operates as a discrete NPN bipolar junction transistor optimized for low-voltage saturation in medium-power linear and switching applications. Its design emphasizes high DC current gain (h_FE = 70–150 at I_C = 1–2 A) and robust thermal performance with T_J(max) = +150°C and R_θJA = 62.5 °C/W.

It supports stable operation across -55°C to +150°C junction temperature range and delivers f_T = 150 MHz at I_C = 100 mA, enabling use in moderate-frequency switching circuits where gain-bandwidth trade-offs are managed via external base drive control.

Key Specifications

Pinout & Package

SOT-223 package with standard lead frame configuration: emitter tab connected to Pin 1 (Emitter), Pin 2 (Base), Pin 3 (Collector), and Pin 4 (Collector tab - electrically tied to Pin 3).

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZXTN2020Z and MJD122, the FZT649 uniquely balances 3 A capability, 300 mV saturation, and SOT-223 thermal performance - making it optimal for space-constrained 1–3 A switching where TO-220 is impractical and sub-250 mV loss is not required.

Availability

FZT649 is available at Aetrix Electronics and suitable for DC-DC converters, automotive body control modules, and industrial PLC output drivers requiring stable component supply despite its discontinued status through legacy channel sourcing.

Supply support for FZT649 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 discrete solutions for automotive, industrial, and cloud infrastructure markets.

The FZT649 belongs to ON Semiconductor's legacy discrete power transistor portfolio, originally developed by Fairchild Semiconductor to address cost-sensitive, medium-current switching needs in consumer and industrial power supplies.

FAQ

What is the maximum continuous collector current rating for the FZT649?

The FZT649 has a maximum continuous collector current (I_C) rating of 3 A at T_A = 25°C. This rating assumes proper PCB thermal management via the SOT-223 collector tab. At elevated ambient temperatures or with reduced copper area, derating is required per the R_θJA = 62.5 °C/W specification. The FZT649 datasheet confirms this value under steady-state conditions with no pulsed operation assumed.

Is the FZT649 still in active production?

No, the FZT649 is officially discontinued by ON Semiconductor, as stated in the datasheet revision "fzt649.lwpPrNC 1/2026 rev3". However, Aetrix Electronics maintains limited legacy inventory and supports traceable sourcing through authorized channels. Customers should plan for long-term obsolescence mitigation while using the FZT649 in existing designs.

What is the typical V_CE(sat) of the FZT649 at 1 A collector current?

The typical V_CE(sat) of the FZT649 is 300 mV at I_C = 1 A and I_B = 100 mA, with a maximum of 600 mV under worst-case conditions. This value is measured at T_A = 25°C and reflects the device's low-saturation design. The FZT649 achieves this performance while maintaining h_FE ≥ 70, enabling efficient switching in 5 V and 12 V systems.

Which package does the FZT649 use, and how is thermal management implemented?

The FZT649 uses the SOT-223 surface-mount package, with Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector, and Pin 4 = Collector thermal tab. Thermal management relies on soldering the exposed collector tab (Pin 4) directly to a large PCB copper pour, achieving R_θJA = 62.5 °C/W. This design allows the FZT649 to dissipate up to 2 W continuously with appropriate board layout - a key feature confirmed in the official ON Semiconductor datasheet for FZT649.

Can the FZT649 replace a MOSFET in low-side switching applications?

The FZT649 can replace a MOSFET only in specific low-frequency, medium-current linear or saturated-switching applications where gate drive simplicity and cost outweigh efficiency needs. Unlike MOSFETs, the FZT649 requires significant base current (e.g., 100 mA for 1 A I_C) and exhibits higher conduction loss than modern logic-level MOSFETs. Its use in place of a MOSFET is justified only when BJT characteristics - such as predictable h_FE and ruggedness under transient overloads - are explicitly required in the FZT649 application context.