onsemi FMBS5551

Overview

FMBS5551 from Fairchild Semiconductor is an NPN general-purpose bipolar junction transistor (BJT) designed for high-voltage amplification and gas discharge display driver applications. It features a 160 V V_CEO, 600 mA continuous collector current, 100–300 MHz f_T, and SuperSOT™-6 package with six terminals including two collectors and one emitter.

For engineers reviewing the FMBS5551 datasheet, pinout, applications, or equivalent options, key selection considerations include its dual-collector configuration for current sharing or cascode operation, high breakdown voltage for display segment driving, low V_CE(sat) at 10 mA/1 mA drive, and thermal resistance of 180°C/W on standard PCB layout.

Technical Context

The FMBS5551 integrates two independent collector terminals (C1 and C2) connected to a shared base and emitter-enabling parallel current handling or cascode biasing without external wiring. Its 180 V V_CBO and 160 V V_CEO support operation in high-voltage display matrix drivers and line-level analog amplifiers.

Designed for stable gain across temperature, it delivers h_FE = 80–250 at I_C = 1–10 mA and maintains f_T ≥ 100 MHz up to 125°C. The device exhibits low noise (NF = 8.0 dB) and minimal capacitance (C_obo = 6.0 pF, C_ibo = 20 pF), supporting wideband small-signal amplification.

Key Specifications

Pinout & Package

FMBS5551 uses the SuperSOT™-6 surface-mount package (3.0 × 1.7 × 1.0 mm), featuring six terminals in a single-row leadframe: Pin 1 = Emitter (E), Pins 2 & 3 = Collector 1 (C1) and Collector 2 (C2), Pin 4 = Base (B), Pin 5 = NC (no internal connection), Pin 6 = Emitter (E). The dual-emitter and dual-collector topology supports redundant current paths or differential pair implementation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN high-voltage amplifier applications.

Compared with MPSA42 and ZTX653, the FMBS5551 uniquely offers dual collectors in a compact SuperSOT™-6 package-providing current redundancy and layout flexibility unmatched by single-collector alternatives, while maintaining competitive voltage, speed, and thermal specs for display and industrial control use cases.

Availability

FMBS5551 is available at Aetrix Electronics and suitable for gas discharge display drivers, high-voltage linear amplifiers, cascode current mirrors, and industrial relay drivers requiring stable component supply and long-lifecycle availability.

Supply support for FMBS5551 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 semiconductor company specializing in power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016.

The FMBS5551 belongs to Fairchild's SuperSOT™-6 discrete BJT product line, engineered for high-voltage, medium-current applications in industrial controls, legacy display systems, and precision analog circuitry.

FAQ

What is the function of Pin 5 (NC) on the FMBS5551?

Pin 5 on the FMBS5551 is explicitly designated as "NC" (No Connection) in the official Fairchild datasheet and has no internal electrical connection. It must remain unconnected in PCB layout to avoid unintended coupling or mechanical stress on the leadframe. Leaving Pin 5 floating or soldering it to ground or any other net may compromise device reliability or thermal performance. This isolation is confirmed in the Absolute Maximum Ratings and Package Dimensions sections of the Rev. A1 datasheet.

Can FMBS5551 be used as a direct replacement for a standard NPN transistor like 2N3904?

No, the FMBS5551 is not a drop-in replacement for the 2N3904 due to fundamental structural and electrical differences. While both are NPN BJTs, the FMBS5551 features dual collectors (C1/C2), dual emitters (E/E), and a 160 V V_CEO, whereas the 2N3904 is a single-collector device rated for only 40 V V_CEO and 200 mA I_C. Substituting FMBS5551 into a 2N3904 circuit risks overdesign, incorrect biasing, and potential misconnection of the NC pin or redundant emitter.

What does the "SuperSOT™-6" package designation mean for FMBS5551?

The SuperSOT™-6 package for FMBS5551 is a proprietary Fairchild surface-mount outline measuring 3.0 × 1.7 × 1.0 mm, with six gull-wing leads in a single row. It integrates dual collector and dual emitter terminals plus base and NC within this compact footprint-enabling current-sharing and thermal spreading not possible in standard SOT-23 or SOT-223 packages. The "SuperSOT" branding indicates optimized thermal and electrical performance relative to legacy SOT formats.

How does the dual-collector configuration of FMBS5551 improve thermal performance?

The dual-collector configuration in FMBS5551 allows current to be split between C1 and C2, reducing current density and localized heating at each collector junction. When both collectors are paralleled in layout, total power dissipation remains unchanged but thermal gradient across the die is lowered. Combined with dual emitters (Pins 1 and 6), this architecture improves effective thermal resistance-verified by Fairchild's 180°C/W R_θJA rating measured on a 1 in² 2 oz copper pad.

Is FMBS5551 suitable for automotive applications?

The FMBS5551 is not qualified to AEC-Q101 or automotive-grade reliability standards. Its datasheet specifies operating junction temperature from –55°C to +150°C, but Fairchild did not subject it to automotive qualification testing (e.g., HTOL, temperature cycling, or ESD robustness per AEC requirements). For automotive use, designers should select AEC-Q101–qualified alternatives such as the ON Semiconductor NSS12201LT1G or Zetex ZTX653Q, which share similar voltage/current specs but include full automotive validation.