FDN337N - 30V 2.2A N-Channel MOSFET SOT-23 | onsemi
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FDN337N Overview
A power MOSFET is a voltage-controlled semiconductor switch used throughout power management hierarchies - from low-side load switches and relay drivers up to DC-DC converter stages. Logic-level MOSFETs like the FDN337N are a sub-class whose gate threshold is low enough for the gate to be driven directly from microcontroller or logic IC outputs (3 V to 5 V rails) without a dedicated gate-driver stage, simplifying circuit design and reducing bill-of-materials cost.
The defining feature of the FDN337N is onsemi (formerly Fairchild Semiconductor) proprietary high-cell-density DMOS technology. This very high density silicon process is specifically tailored to minimize on-state resistance, which reduces conduction losses and in-line power loss in the small SOT-23 body. Logic-level gate drive is the second headline feature, allowing direct interfacing with 3 V and 5 V control logic common in portable systems.
According to the onsemi datasheet, the device is particularly suited for low-voltage, battery-powered applications such as notebook computers, portable phones, and PCMCIA cards, where fast switching speed and low in-line power loss are required in a very small surface-mount package. The 30 V VDS rating provides comfortable headroom on 12 V and multi-cell battery rails.
Typical applications include low-side load switching in portable electronics, relay and solenoid drivers, battery management disconnect switches, and general-purpose logic-level switching in consumer and industrial boards.
When designing with this part, verify the gate-drive amplitude against the datasheet RDS(on) test conditions, since on-resistance at 2.5 V drive is higher than at 4.5 V or 10 V drive, directly affecting conduction loss and junction temperature.
This page synthesizes distributor listings, second-source drop-in options, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for FDN337N — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
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FDN337N-NL
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View Datasheet →FDN337N
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View Datasheet →FDN337N Maximum Ratings & Electrical Characteristics
| Transistor Type | N-Channel MOSFET |
| Operating Mode | Enhancement Mode, Logic Level |
| Drain-Source Voltage (VDS) | 30 V |
| Continuous Drain Current (ID) | 2.2 A at Ta |
| Power Dissipation (PD) | 500 mW at Ta |
| Technology | High Cell Density DMOS |
| Package | SOT-23 (SuperSOT-3), 3-pin surface mount |
| Mounting Type | Surface Mount |
| Typical Applications | Notebook computers, portable phones, PCMCIA cards, battery-powered circuits |
FDN337N Pin Configuration
| Pin 1 | G — Gate - logic-level control input |
| Pin 2 | S — Source - connected to ground in low-side switching |
| Pin 3 | D — Drain - connected to load |
Safe Operating Area
Typical Applications
FDN337N is suitable for 6 applications: Notebook Computer Load Switching, Portable Phone Battery-Powered Circuits, PCMCIA Card and Hot-Swap Slots, Relay and Solenoid Drivers, Battery Management Disconnect Switches, General-Purpose Logic-Level Switching.
Notebook Computer Load Switching
The FDN337N fits notebook computer power distribution directly because the onsemi datasheet names portable computing as a primary application. In a notebook, it serves as a low-side or load switch on 12 V-class rails, where the 30 V VDS rating provides ample margin over battery pack voltages and the 2.2 A continuous current covers moderate subsystem loads such as card slots and peripherals. Its high-cell-density DMOS construction keeps on-state resistance low, so in-line conduction loss stays small across the many hours a portable system runs on battery. The logic-level gate connects to embedded controller GPIO without a driver IC, saving board area and cost. Designers should verify RDS(on) at the controller actual drive voltage and add copper pour to hold dissipation well under the 500 mW Ta rating.
Recommended
Portable Phone Battery-Powered Circuits
In portable phone and handheld device boards, the FDN337N acts as a battery disconnect or peripheral power switch on single-cell or multi-cell rails. The datasheet explicitly cites portable phones and other battery-powered circuits as target uses, and the reasoning is clear: the SOT-23 outline occupies a few square millimeters, the enhancement-mode logic-level gate switches directly from baseband or PMIC GPIO, and DMOS on-state resistance minimizes the in-line drop that would otherwise waste battery energy as heat. Fast switching also suits the frequent load on/off cycling of wireless subsystem power gating. At typical phone load currents well below 2.2 A, junction heating is negligible, but the designer should still keep the gate tied through a pull-down so the FET cannot float on during reset states.
Recommended
PCMCIA Card and Hot-Swap Slots
PCMCIA card slots were a cited application in the original Fairchild datasheet because card hot-swap switching demands exactly what the FDN337N provides: a tiny footprint, logic-level gate drive from the slot controller, 30 V surge tolerance, and fast switching to limit inrush transients. In a hot-swap path the FET toggles as cards insert and remove, so low gate charge from the DMOS cell structure keeps switching losses small across repeated operations. The 2.2 A continuous rating comfortably handles legacy 16-bit card currents with margin. For modern equivalents such as ExpressCard or SD-slot power switches, the same topology applies; add soft-start RC shaping on the gate if inrush limiting is required, and verify flyback clamping for inductive card loads.
Recommended
Relay and Solenoid Drivers
The FDN337N makes an economical low-side relay and solenoid driver on 12 V rails. The 30 V drain-source rating absorbs the rail voltage plus headroom while a flyback diode clamps coil inductive kick; the logic-level gate lets a microcontroller pin energize the coil directly through a small series resistor, eliminating a driver stage. With typical small relays drawing 30 to 100 mA, conduction loss (I squared times RDS(on)) is tens of milliwatts, far below the 500 mW package rating, so thermal design is trivial. The high cell density DMOS process keeps saturation voltage low, ensuring the coil sees nearly the full supply. Place the FET close to the coil, keep the gate loop short for clean switching, and add a gate pull-down for defined power-up state.
Recommended
Battery Management Disconnect Switches
In multi-cell battery packs and low-voltage battery management systems, the FDN337N serves as a low-side disconnect protecting against deep discharge or fault conditions. Its 30 V rating suits two- and three-cell lithium stacks with margin, the 2.2 A rating covers small-pack applications such as power banks and portable instruments, and the logic-level gate interfaces directly to the battery monitor IC or fuel-gauge GPIO. Because the switch conducts continuously, on-state resistance from the DMOS process is the key parameter: every milliohm is a standing efficiency loss. Estimate pack-side loss as I squared times RDS(on) at the minimum gate drive available in the system, and ensure the gate can be forced off by the protection IC during fault shutdown with a defined pull-down.
Recommended
General-Purpose Logic-Level Switching
Beyond the cited portable applications, the FDN337N is a workhorse for general-purpose low-side switching of LEDs, fans, buzzers, level translation, and peripheral power gating on industrial and consumer boards. The combination of a 30 V rating, 2.2 A capability, logic-level threshold, and the ubiquitous SOT-23 footprint makes it the default choice when a designer needs something stronger than a 2N7002 but does not want to grow the package. Fast switching from low gate charge suits PWM dimming and fan speed control, and the small outline supports dense mixed-signal layouts. Verify drive amplitude against RDS(on) test conditions for predictable thermals, and reserve a larger DPAK part when continuous current approaches the 2.2 A Ta limit.
Recommended
Recommended Products Summary
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Engineering reference data for FDN337N — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | FDN337N-NL | FDN337N (UMW) | FDN337N (Fuxinsemi) |
|---|---|---|---|---|
| Package | SOT-23 (SuperSOT-3) | SOT-23 (SuperSOT-3) - same | SOT-23 - same | SOT-23 - same |
| Brand | onsemi | onsemi (Fairchild legacy) | UMW | Fuxinsemi |
| Drain-Source Voltage | 30 V | 30 V | 30 V | 30 V |
| Continuous Drain Current | 2.2 A (Ta) | 2.2 A (Ta) | 2.2 A | 2.2 A |
| Gate Drive | Logic Level | Logic Level | Logic Level | Logic Level |
| Pinout (G-S-D) | Pin 1 G, Pin 2 S, Pin 3 D | Pin 1 G, Pin 2 S, Pin 3 D - identical | Standard SOT-23 G-S-D - identical | Standard SOT-23 G-S-D - identical |
Key Differentiators
- High-cell-density DMOS process minimizes on-state resistance (vs 2N7002)
- Logic-level gate drive eliminates driver stage (vs Standard-threshold SOT-23 MOSFETs)
- Multi-source availability under the same part number (vs FDN337N (UMW) / FDN337N (Fuxinsemi))
Design Notes
Estimated: conduction loss equals I^2 x RDS(on) evaluated at the actual applied VGS, not the datasheet best-case number. With the 500 mW at Ta package rating, a 2 A continuous load requires RDS(on) low enough that the product stays below roughly 125 mW, leaving margin for switching loss and ambient derating. At lower currents (under 500 mA), thermals are a non-issue. Always check the RDS(on) versus VGS and versus temperature curves in the onsemi datasheet; resistance rises with junction temperature, creating a mild positive feedback that must have margin.
Keep the gate loop short: route the GPIO-to-gate trace away from the drain switching node to prevent capacitive coupling that can falsely turn the FET on during fast drain edges. Add a 100k gate-to-source pull-down so the device has a defined off-state during microcontroller reset or power sequencing. Copper pour on the source and drain pins of the SOT-23 improves dissipation capability beyond the free-air 500 mW figure and reduces drain-node impedance for cleaner switching edges.
Three recurring mistakes with SOT-23 logic-level FETs: (1) substituting a standard-threshold part that never fully enhances at 3 V drive - the FDN337N is logic level, preserve that property in substitutes; (2) omitting the flyback clamp when driving relay or solenoid coils, allowing the drain to exceed the 30 V VDS rating on inductive kick; (3) floating the gate during startup, causing uncontrolled partial conduction. Fix all three with a defined gate pull-down, a clamp diode for inductive loads, and verification of threshold behavior at your minimum drive voltage.
Compliance Information
Current onsemi FDN337N production is a lead-free part (the legacy -NL no-lead variant designation is now absorbed into standard production). REACH, halogen-free, and conflict-minerals statements should be confirmed via the onsemi compliance report.
