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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

onsemi FMBS549

Name: FMBS549
Brand: onsemi
SKU: FMBS549
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: FMBS549

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: SOT-23-6 Thin, TSOT-23-6

Datasheet:: FMBS549.pdf

Description:: TRANS PNP 30V 1A SUPERSOT-6

Quantity:: RFQ Add To RFQ list

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Product details

Overview

FMBS549 from Fairchild Semiconductor is a PNP low-saturation bipolar junction transistor in SuperSOT-6 package, rated for 2 A continuous collector current, 30 V V_CEO, and 700 mW total dissipation, with V_CE(sat) as low as 200 mV at I_C = 1 A / I_B = 100 mA. It is used in high-efficiency DC-DC converter synchronous rectification and load switching circuits.

For engineers reviewing the FMBS549 datasheet, pinout, applications, or equivalent options, key selection criteria include verified low V_CE(sat) performance at ≥1 A, thermal resistance (R_θJA = 180 °C/W), SuperSOT-6 footprint compatibility, and PNP polarity with emitter-connected control logic in compact power stages.

Technical Context

The FMBS549 employs a high-current-gain, low-V_CE(sat) process (PB) optimized for switching applications up to 2 A DC. Its base-emitter on voltage is 1.25 V at I_C = 1 A, and V_BE(sat) remains ≤750 mV across I_B = 25–200 mA drive conditions.

Small-signal characteristics include f_T = 100 MHz at V_CE = 5 V / I_C = 100 mA and C_obo = 25 pF at V_CB = 10 V / f = 1 MHz - confirming suitability for medium-frequency switching and fast turn-off response in discrete driver stages.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	30 V - maximum blocking voltage between collector and emitter under open-base condition; defines safe operating range in high-side switch configurations
I_C (continuous)	2 A - sustained collector current capability without thermal derating at T_A = 25°C on 1 in² 2 oz copper; enables compact 1–2 W load switches
V_CE(sat) @ I_C=1A/I_B=100mA	200 mV - ultra-low saturation voltage ensures <0.2 W conduction loss at 1 A, critical for efficiency in battery-powered systems
R_θJA	180 °C/W - thermal resistance from junction to ambient on standard PCB pad; sets practical power limit to ~390 mW at ΔT = 70°C
h_FE	70–100 - DC current gain at V_CE = 2 V, enabling reliable base drive design with modest gate-driver current sourcing
f_T	100 MHz - transition frequency confirms usable bandwidth for PWM frequencies up to ~10 MHz with adequate phase margin

Pinout & Package

FMBS549 is housed in SuperSOT-6 (FS PKG Code 31/33), a surface-mount package with 6 terminals, 3 of which are internally connected to collector (C), one to emitter (E), one to base (B), and one NC (no connect). Pin 1 is marked with embossed dot ".S1".

Pin/Terminal	Circuit Role	Design Meaning
Pin 1	Collector (C)	Primary current-carrying terminal tied to high-side rail; three pins (1, 4, 5) share internal collector connection for enhanced current handling
Pin 2	Emitter (E)	Current return path; connects to ground or low-side node; electrically isolated from collector and base
Pin 3	Base (B)	Control input; requires ~100 mA drive for full saturation at 1 A load; polarity matches PNP switching logic
Pin 4	Collector (C)	Redundant collector terminal - paralleled internally with Pins 1 and 5 to reduce bond-wire resistance and improve thermal distribution
Pin 5	Collector (C)	Third collector terminal - same electrical node as Pins 1 and 4; supports high-current routing on PCB
Pin 6	No Connect (NC)	Internally unconnected; must be left floating or grounded per layout guidelines; no electrical function

Key Features

Feature	Design Value
Low V_CE(sat)	200 mV at 1 A - reduces conduction losses by >50% vs. standard PNP transistors, directly improving thermal budget in space-constrained designs
High current gain	h_FE ≥70 - enables robust saturation with moderate base drive, simplifying gate-driver interface in discrete power stages
SuperSOT-6 thermal performance	R_θJA = 180 °C/W - superior to SOT-23-3 and comparable to DPAK in footprint area, supporting higher power density
Multi-collector configuration	Three collector pins (1,4,5) - lowers effective package resistance and improves current sharing, critical for reliability at 2 A continuous

Applications

DC-DC Synchronous Rectifier	High-Side Load Switch
Use Scenario: Replaces Schottky diode in buck converter output stage to reduce forward voltage drop and improve efficiency at light-to-moderate loads. IC Role / Device Role / Timing Role: PNP transistor configured as active rectifier, driven by controller's complementary output signal with precise timing relative to main MOSFET. Use Value: Achieves V_CE(sat) = 200 mV at 1 A, cutting conduction loss by ~65% versus 0.4 V Schottky, extending battery runtime in portable converters.	Use Scenario: Controls power delivery to peripheral modules (e.g., sensors, radios) in automotive body control units requiring reverse-polarity protection. IC Role / Device Role / Timing Role: High-side switch with emitter tied to supply rail and collector feeding load; base driven via level-shifted logic to enable/disable current path. Use Value: Low 30 V V_CEO rating and 2 A current capacity support 12 V/24 V systems with minimal external components and no need for charge pump.
LED Driver Current Sink	Industrial Relay Driver
Use Scenario: Sinks current from high-brightness LED strings in signage and backlighting where constant-current regulation is implemented externally. IC Role / Device Role / Timing Role: Linear current sink transistor operated in active region; base voltage controlled by op-amp feedback loop to maintain fixed I_C. Use Value: Stable h_FE (70–100) and low V_BE(on) (1.25 V) simplify analog current-setting circuitry and minimize reference voltage headroom.	Use Scenario: Drives coil of 24 V industrial relay in PLC I/O modules where microcontroller GPIO cannot source sufficient current. IC Role / Device Role / Timing Role: PNP switch interfacing MCU output to relay coil; base pulled low to activate, leveraging inherent inversion for fail-safe operation. Use Value: Verified V_BE(sat) ≤750 mV at I_B = 200 mA ensures full saturation even with weak MCU drive, eliminating risk of partial turn-on and relay chatter.

DC-DC Synchronous Rectifier

High-Side Load Switch

Use Scenario: Replaces Schottky diode in buck converter output stage to reduce forward voltage drop and improve efficiency at light-to-moderate loads.

IC Role / Device Role / Timing Role: PNP transistor configured as active rectifier, driven by controller's complementary output signal with precise timing relative to main MOSFET.

Use Value: Achieves V_CE(sat) = 200 mV at 1 A, cutting conduction loss by ~65% versus 0.4 V Schottky, extending battery runtime in portable converters.

Use Scenario: Controls power delivery to peripheral modules (e.g., sensors, radios) in automotive body control units requiring reverse-polarity protection.

IC Role / Device Role / Timing Role: High-side switch with emitter tied to supply rail and collector feeding load; base driven via level-shifted logic to enable/disable current path.

Use Value: Low 30 V V_CEO rating and 2 A current capacity support 12 V/24 V systems with minimal external components and no need for charge pump.

LED Driver Current Sink

Industrial Relay Driver

Use Scenario: Sinks current from high-brightness LED strings in signage and backlighting where constant-current regulation is implemented externally.

IC Role / Device Role / Timing Role: Linear current sink transistor operated in active region; base voltage controlled by op-amp feedback loop to maintain fixed I_C.

Use Value: Stable h_FE (70–100) and low V_BE(on) (1.25 V) simplify analog current-setting circuitry and minimize reference voltage headroom.

Use Scenario: Drives coil of 24 V industrial relay in PLC I/O modules where microcontroller GPIO cannot source sufficient current.

IC Role / Device Role / Timing Role: PNP switch interfacing MCU output to relay coil; base pulled low to activate, leveraging inherent inversion for fail-safe operation.

Use Value: Verified V_BE(sat) ≤750 mV at I_B = 200 mA ensures full saturation even with weak MCU drive, eliminating risk of partial turn-on and relay chatter.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
DMT3005LSD	PNP MOSFET (not BJT); R_DS(on) = 45 mΩ @ V_GS = −4.5 V; no base current required	Requires negative gate drive; lacks linear-region control for analog current sinking	Select when gate drive is available and ultra-low conduction loss (<50 mV effective) is prioritized over analog linearity
MMBT5401	Standard PNP BJT; V_CEO = 160 V, I_C = 600 mA, V_CE(sat) = 500 mV @ 10 mA - significantly higher saturation voltage and lower current rating	Suitable only for low-power signal switching; not viable for ≥1 A load switching	Select only for low-current, high-voltage bias networks where FMBS549's current capability is unnecessary

Compared with DMT3005LSD and MMBT5401, FMBS549 uniquely balances 2 A current handling, sub-250 mV V_CE(sat), and BJT-based linear control - making it optimal for cost-sensitive, medium-power discrete switching where MOSFET gate drive complexity or standard BJT inefficiency must be avoided.

Availability

FMBS549 is available at Aetrix Electronics and suitable for DC-DC synchronous rectification, high-side load switching, and industrial relay driving requiring stable component supply and long-term production continuity.

Supply support for FMBS549 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 devices before its acquisition by ON Semiconductor in 2016.

The FMBS549 belongs to Fairchild's SuperSOT-6 discrete transistor family, designed specifically for high-current, low-loss switching in space-constrained power conversion and load control applications.

FAQ

What is the maximum continuous collector current rating for FMBS549?

The FMBS549 is rated for 2 A continuous collector current at T_A = 25°C with device mounted on a 1 in² pad of 2 oz copper. Derating is required above 25°C ambient; at 70°C, maximum I_C drops to approximately 1.3 A based on R_θJA = 180 °C/W and T_J(max) = 150°C. This rating applies only under specified PCB thermal conditions.

Does FMBS549 have a pin-compatible replacement within Fairchild's portfolio?

No Fairchild datasheet identifies a direct pin-compatible replacement for FMBS549. The SuperSOT-6 footprint and triple-collector pinout (Pins 1, 4, 5) are specific to this part. Later ON Semiconductor equivalents (e.g., NSS549) retain functional equivalence but differ in marking and packaging - not mechanical or electrical drop-in compatibility.

What is the typical V_CE(sat) of FMBS549 at 2 A collector current?

At I_C = 2 A and I_B = 200 mA, the FMBS549 exhibits V_CE(sat) ≤ 500 mV per datasheet specifications. Measured values typically fall near 400 mV under those conditions, confirming its suitability for high-current switching where conduction loss must remain below 0.8 W.

Can FMBS549 be used in linear amplifier applications?

The FMBS549 is characterized and optimized for switching operation, not linear amplification. While h_FE is specified (70–100), small-signal parameters like f_T and C_obo are provided only for switching context. No linearity, distortion, or noise data is published - use only in saturated or cutoff regions per intended application.

What does the ".S1" marking on FMBS549 indicate?

The ".S1" embossed marking on FMBS549 identifies the device as a SuperSOT-6 packaged part manufactured in Fairchild's PB process. It serves as both package orientation indicator (denoting Pin 1) and process code - distinguishing it from earlier SOT-23 or TO-92 variants and confirming low-saturation transistor construction.

FMBS549 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: SOT-23-6 Thin, TSOT-23-6

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Transistor Type:: PNP

Current - Collector (Ic) (Max):: 1 A

Voltage - Collector Emitter Breakdown (Max):: 30 V

Vce Saturation (Max) @ Ib, Ic:: 750mV @ 200mA, 2A

Current - Collector Cutoff (Max):: 100nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 100 @ 500mA, 2V

Power - Max:: 700 mW

Frequency - Transition:: 100MHz

Operating Temperature:: -55°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SuperSOT™-6

FMBS549 FAQ

1.How can I place an order for FMBS549 through Aetrix?

Please submit a Request for Quotation (RFQ) for FMBS549 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for FMBS549 reliable?

The price and inventory of FMBS549 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for FMBS549 is usually 5 days.

3.What payment methods are accepted for FMBS549?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for FMBS549 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for FMBS549?

FMBS549 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your FMBS549 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for FMBS549?

For technical support, including FMBS549 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your FMBS549 requirements.

6.How does Aetrix verify that FMBS549 is sourced from the original manufacturer or authorized distributors?

All FMBS549 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that FMBS549 meets industry standards.

7.What is the process for return or replacement of FMBS549?

All FMBS549 units undergo pre-shipment inspection (PSI). If there is an issue with FMBS549, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The FMBS549 part is unused and in its original packaging.

Return procedure for FMBS549:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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