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onsemi FJX3904TF
- Part No.:
- FJX3904TF
- Manufacturer:
- onsemi
- Category:
- Single Bipolar Transistors
- Package:
- SC-70, SOT-323
- Datasheet:
-
FJX3904TF.pdf
- Description:
- TRANS NPN 40V 0.2A SOT-323
- Quantity:
- Payment:
- Shipping:
Inventory:5,699
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Product details
Overview
FJX3904TF from ON Semiconductor is an NPN epitaxial silicon transistor in SC-70 package, rated for 40 V VCEO, 200 mA IC, and 350 mW PC, with DC current gain (hFE) ranging from 40 to 300 depending on operating point - used in general-purpose switching and amplification circuits in portable power management and signal conditioning stages.
For engineers reviewing the FJX3904TF datasheet, pinout, applications, or equivalent options, this page delivers verified electrical specs, thermal behavior, saturation voltage performance at 10–50 mA, 300 MHz fT, and SC-70 footprint compatibility for space-constrained PCB designs.
Technical Context
This discrete NPN transistor operates as a low-voltage, medium-current switch or small-signal amplifier with VBE(sat) ≤ 0.85 V at IC = 10 mA / IB = 1 mA and VCE(sat) ≤ 0.3 V at IC = 50 mA / IB = 5 mA. Its 4 pF Cob and 300 MHz fT support high-frequency switching up to ~100 MHz in Class-A or saturated-mode configurations.
Thermal design is constrained by RθJA = 357 °C/W on standard FR-4 board (76 × 114 mm), requiring derating of 2.8 mW/°C above 25°C ambient. Junction temperature must remain ≤150°C under steady-state operation, limiting continuous IC at elevated ambient temperatures.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCEO | 40 V - Maximum collector-emitter voltage before breakdown; sets upper limit for supply rail in low-voltage switching applications. |
| IC | 200 mA - Continuous collector current rating; defines maximum load drive capability in saturated switch mode. |
| PC | 350 mW - Total power dissipation at 25°C ambient; determines thermal margin before derating begins. |
| hFE | 40–300 - DC current gain range across 0.1–100 mA IC; impacts base drive requirements and bias stability. |
| fT | 300 MHz - Current gain bandwidth product; enables use in RF preamps or fast digital switching up to ~100 MHz. |
| Cob | 4 pF - Output capacitance at VCB = 5 V; limits high-frequency gain and switching speed in tuned circuits. |
Pinout & Package
Package: SC-70 (SOT-323), 3-lead surface-mount plastic package with 1.25 mm body width; marked "S1A" on top surface; tape-and-reel packaging (3,000 units per reel).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | Base | Control terminal for forward-biased junction; requires ~0.7 V VBE and sufficient IB to saturate at target IC. |
| 2 | Emitter | Current return path; tied to ground or low-side reference in common-emitter configuration. |
| 3 | Collector | Output current sink; connects to load and positive supply in low-side switch topology. |
Key Features
| Feature | Design Value |
|---|---|
| Low VCE(sat) | 0.2 V at IC = 10 mA / IB = 1 mA - reduces conduction loss and self-heating in battery-powered switches. |
| High fT | 300 MHz - supports broadband amplification and fast edge-rate digital switching without excessive phase lag. |
| Small-footprint SC-70 | 1.25 mm × 2.1 mm body - enables dense layout in wearables, IoT sensors, and compact power regulators. |
| Low noise figure | 5 dB at 100 μA / 5 V - suitable for low-level analog signal amplification where SNR preservation matters. |
Applications
| Portable LED Driver | Low-Voltage Logic Level Shifter |
|---|---|
|
Use Scenario: Driving white LEDs from 3.3 V microcontroller GPIO pins in fitness trackers and smart badges. IC Role / Device Role / Timing Role: Low-side saturated switch controlling LED current via PWM duty cycle. Use Value: VCE(sat) ≤ 0.3 V at 50 mA ensures >90% efficiency and minimal thermal rise in 1.6 mm² PCB area. |
Use Scenario: Translating 1.8 V logic outputs to 3.3 V input thresholds in mixed-voltage MCU peripherals. IC Role / Device Role / Timing Role: Active pull-up NPN switch enabling bidirectional level translation without external resistors. Use Value: 300 MHz fT and 70 ns tON support clean 10 MHz data transfer between voltage domains. |
| Audio Pre-amplifier Stage | Load Switch for Sensor Biasing |
|
Use Scenario: Amplifying microphone signals in voice-activated remote controls before ADC sampling. IC Role / Device Role / Timing Role: Common-emitter small-signal amplifier with emitter degeneration for linearity. Use Value: 5 dB NF and hFE ≥ 100 at 100 μA enable high-SNR gain without added op-amp complexity. |
Use Scenario: Enabling/disabling bias current to MEMS pressure sensors during sleep/wake cycles. IC Role / Device Role / Timing Role: High-efficiency, low-leakage load switch replacing larger MOSFETs or dedicated load switches. Use Value: ICEX ≤ 50 nA at VCE = 30 V minimizes standby power drain in battery-critical systems. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar NPN transistor applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MMBT3904LT1G | Same SC-70 package, identical pinout, but hFE min = 100 @ IC = 10 mA (vs. FJX3904TF's 70); slightly higher VCE(sat) (0.3 V vs. 0.2 V @ 10 mA). | Better gain consistency for linear amplification; less optimal for ultra-low-loss switching at light loads. | Select MMBT3904LT1G when hFE stability across production lots is critical; retain FJX3904TF for lowest VCE(sat) at 10 mA. |
| DXT3904TC | SC-89 package (smaller footprint), same electrical specs, but RθJA = 400 °C/W (vs. 357 °C/W); no tape-and-reel option below 10k units. | Higher thermal resistance limits continuous IC in thermally constrained layouts; not drop-in due to different land pattern. | Choose DXT3904TC only when board area is <1.0 mm² per device and thermal derating is acceptable; otherwise prefer FJX3904TF for manufacturability. |
Compared with MMBT3904LT1G and DXT3904TC, the FJX3904TF offers the lowest VCE(sat) at 10 mA and best thermal resistance in SC-70, making it optimal for high-efficiency, medium-current switching where layout space and thermal headroom are balanced constraints.
Availability
FJX3904TF is available at Aetrix Electronics and suitable for portable LED drivers, low-voltage logic level shifters, audio pre-amplifier stages, and sensor load switching requiring stable component supply and consistent SC-70 footprint compatibility.
Supply support for FJX3904TF 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 specializing in energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and consumer markets.
The FJX3904TF belongs to ON Semiconductor's legacy Fairchild discrete transistor portfolio, designed for cost-sensitive, space-constrained general-purpose switching and amplification in battery-powered and interface-critical applications.
FAQ
What is the maximum continuous collector current for FJX3904TF?
The FJX3904TF has an absolute maximum collector current (IC) rating of 200 mA at TA = 25°C. However, actual usable current depends on thermal conditions: with RθJA = 357 °C/W and TJ(max) = 150°C, sustained operation above ~120 mA requires significant board-level heat sinking or ambient derating. The FJX3904TF datasheet specifies 200 mA as a stress limit, not a recommended continuous operating value.
Does FJX3904TF support high-frequency switching applications?
Yes, the FJX3904TF supports high-frequency switching with a current gain bandwidth product (fT) of 300 MHz and turn-on/turn-off times of 70 ns and 250 ns respectively. These parameters allow reliable operation in digital signal routing, PWM-driven LED dimming, and RF pre-amplifier stages up to ~100 MHz. The FJX3904TF's 4 pF output capacitance further confirms suitability for such applications when properly biased.
What is the SC-70 package marking for FJX3904TF?
The FJX3904TF is marked "S1A" on the top surface of its SC-70 (SOT-323) package. This marking is consistent across production lots and matches the ordering information in the official ON Semiconductor documentation. The FJX3904TF uses standard SC-70 land patterns defined in JEDEC MO-203, with pin 1 (Base) at the left when the marking is read left-to-right.
How does the DC current gain (hFE) of FJX3904TF vary with collector current?
The FJX3904TF exhibits a non-monotonic hFE curve: minimum 40 at IC = 0.1 mA, rising to 70 at 1 mA, peaking at 100–300 between 10–50 mA, then dropping to 60 at 50 mA and 30 at 100 mA. This behavior is confirmed in the FJX3904TF datasheet Figure 1 and affects bias network design - for stable amplification, operate near 1–10 mA; for switching, verify saturation at target IC using the specified hFE range.
Is FJX3904TF suitable for low-noise analog amplification?
Yes, the FJX3904TF has a noise figure (NF) of 5 dB at IC = 100 μA, VCE = 5 V, RS = 1 kΩ, and 10 Hz–15.7 kHz bandwidth - making it suitable for low-noise pre-amplification of microphone or sensor signals. Its low 1/f noise corner and consistent hFE at microamp bias points allow effective use in battery-operated audio front-ends where op-amps would consume more quiescent current than the FJX3904TF.
FJX3904TF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- -
- Package/Case:
- SC-70, SOT-323
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Transistor Type:
- NPN
- Current - Collector (Ic) (Max):
- 200 mA
- Voltage - Collector Emitter Breakdown (Max):
- 40 V
- Vce Saturation (Max) @ Ib, Ic:
- 300mV @ 5mA, 50mA
- Current - Collector Cutoff (Max):
- -
- DC Current Gain (hFE) (Min) @ Ic, Vce:
- 100 @ 10mA, 1V
- Power - Max:
- 350 mW
- Frequency - Transition:
- 300MHz
- Operating Temperature:
- 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- SOT-323
FJX3904TF FAQ
1.How can I place an order for FJX3904TF through Aetrix?
Please submit a Request for Quotation (RFQ) for FJX3904TF 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 FJX3904TF reliable?
The price and inventory of FJX3904TF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for FJX3904TF is usually 5 days.
3.What payment methods are accepted for FJX3904TF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for FJX3904TF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for FJX3904TF?
FJX3904TF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your FJX3904TF 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 FJX3904TF?
For technical support, including FJX3904TF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your FJX3904TF requirements.
6.How does Aetrix verify that FJX3904TF is sourced from the original manufacturer or authorized distributors?
All FJX3904TF 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 FJX3904TF meets industry standards.
7.What is the process for return or replacement of FJX3904TF?
All FJX3904TF units undergo pre-shipment inspection (PSI). If there is an issue with FJX3904TF, 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 FJX3904TF part is unused and in its original packaging.
Return procedure for FJX3904TF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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