MMBF5485 vs AO3402: Component Comparison for Power Electronics Engineers

Quick verdict

For high-frequency, low-current RF switching and amplification up to ~400 MHz, the MMBF5485 is clearly the better choice due to its JFET technology optimized for low noise and RF operation. For general-purpose low-voltage switching and load driving requiring several amps of current, the AO3402 is superior, offering a 30 V rating and continuous drain current up to 4 A with low R_DS(on).

Spec comparison table

SpecMMBF5485AO3402Notes
ConfigurationN-Channel JFETN-Channel MOSFETDifferent transistor technologies; JFET better for RF/noise, MOSFET better for power switching
Current rating (continuous)10 mA4 A (Ta)AO3402 supports 400× higher continuous current, better for power applications
Maximum frequency400 MHzNot specified (low frequency typ 1 MHz)MMBF5485 optimized for RF applications, AO3402 for low-frequency switching
Noise figure4 dBNot specifiedMMBF5485’s 4 dB noise figure suits low-noise RF front ends
Output power maxNot specifiedNot specifiedNo clear data to compare
Mounting typeSurface Mount (SOT-23-3)Surface Mount (SOT-23-3)Both have identical package types
Package caseTO-236-3 / SC-59 / SOT-23-3SOT-23-3 VariantPhysically compatible packages
TechnologyJFETMOSFET (Metal Oxide)JFET better for linear/RF, MOSFET better for power switching
Maximum voltage rating25 V30 VAO3402 can handle 20% higher voltage, useful in more demanding power circuits
Voltage test15 V15 VEqual test voltages
Drain current max (pulsed)Not specified15 AAO3402 can handle high pulsed currents
Power dissipation max (Ta)Not specified1.4 WAO3402 rated for significant power dissipation, MMBF5485 not specified
Gate threshold voltageNot specified0.5 V (min) – 1.5 V (max), typ 1 VAO3402’s threshold voltage well characterized, low gate drive voltage
Gate charge (Q_g)Not specified4.34 nC @ 4.5 V, typ 12 nCAO3402 requires moderate gate charge for switching
R_DS(on) max @ 4A, 10VNot specified55 mΩAO3402 low R_DS(on) suitable for efficient switching at moderate currents
Input capacitance (C_iss)Not specified390 pF @ 15 VAO3402 input capacitance moderate for MOSFET switching
Gate leakage currentNot specified+100 nAAO3402 gate leakage typical MOSFET levels
Turn-on delay timeNot specified3.5 nsAO3402 fast switching suitable for high-speed PWM or switching
Turn-off delay timeNot specified17.5 nsAO3402 turn-off delay typical for MOSFET switching
Junction temperature maxNot specified+150 °CAO3402 supports high junction temperatures for power applications
Thermal resistance (junction to ambient)Not specified125 °C/W maxAO3402 thermal data available, useful for thermal design
Operating temperature rangeNot specified-55°C to +150°CAO3402 designed for wide temperature range
Gate-source voltage maxNot specified±12 VAO3402 gate voltage rating typical for power MOSFET control
Duty cycleNot specified0.5% max (typ), 50%AO3402 suitable for PWM switching with specified duty cycles

Design trade-offs

The MMBF5485 and AO3402 target fundamentally different applications despite sharing the same SOT-23-3 package. The MMBF5485 is a JFET optimized for RF frequencies up to 400 MHz with a low noise figure of 4 dB and extremely low current capability (10 mA max). This makes it suitable for analog RF front ends, small-signal switching, or low-noise amplification circuits. Its JFET technology inherently has a high input impedance and low noise but lacks the current and voltage handling capabilities needed in typical power switching roles.

In contrast, the AO3402 is a power MOSFET designed for low-voltage (30 V max), high-current (4 A continuous, 15 A pulsed) switching applications. It features a low R_DS(on) of 55 mΩ at 4A, which translates into lower conduction losses and better efficiency in DC-DC converters, load switches, and general-purpose switching. Its gate charge (4.34 nC at 4.5 V) and fast switching times (3.5 ns turn-on delay) enable efficient gate drive and high-frequency PWM operation, although it is not meant for RF applications.

From a thermal standpoint, the AO3402’s 1.4 W power dissipation rating and 125 °C/W junction-to-ambient resistance allow it to handle moderate power levels without complex cooling, whereas the MMBF5485 provides no thermal dissipation data but is clearly limited by its low current rating.

Gate drive requirements differ significantly: the AO3402 requires a MOSFET gate driver or at least a logic-level input with 4.5–10 V drive to fully turn on, while the MMBF5485, as a JFET, will bias differently and cannot be driven with MOSFET gate drivers. This impacts firmware and hardware control design—AO3402 can be driven directly from microcontrollers or MOSFET drivers, MMBF5485 often needs biasing networks and careful analog control.

Layout sensitivity is also distinct. The MMBF5485’s RF nature demands careful PCB layout with controlled impedance traces and minimal parasitic capacitance/inductance, while the AO3402 demands low-inductance power paths, proper thermal vias, and decoupling to handle switching currents and reduce EMI.

Cost-wise, the AO3402 is likely less expensive at volume due to its widespread use in power switching, while the MMBF5485’s specialized JFET technology and RF optimization typically come at a premium, although exact pricing is vendor-dependent.

Use-case fit

Choose MMBF5485 when…

Choose AO3402 when…

Drop-in compatibility

Both devices come in SOT-23-3 packages, but the MMBF5485 is a JFET and the AO3402 a MOSFET. Pinouts and internal device construction differ, so they are not pin-compatible nor drop-in replacements. Substituting one for the other would require redesigning the biasing network, gate drive circuitry, and possibly the PCB layout. Without explicit pinout data from the datasheets, assume no direct interchangeability.

Alternatives to consider