UM6K33NTN vs FDC6321C: Component Comparison for Power Electronics Designers
Quick verdict
For low-current, higher-voltage switching applications requiring dual N-channel MOSFETs in a compact package, the UM6K33NTN is preferable due to its 50 V rating and 1.2 V logic-level drive. For mixed-signal or load-switching circuits needing both N and P channels with higher current capability and better conduction losses at 25 V, the FDC6321C is the better choice.
Spec comparison table
| Spec | UM6K33NTN | FDC6321C | Notes |
|---|---|---|---|
| Configuration | 2 × N-Channel | 1 × N-Channel, 1 × P-Channel | FDC6321C offers complementary N/P pair, enabling push-pull or high-side/low-side switching. |
| Continuous Drain Current @ 25°C | 200 mA | 680 mA (N), 460 mA (P) | FDC6321C supports significantly higher current per channel, better for higher load demands. |
| Drain-Source Voltage Max | 50 V | 25 V | UM6K33NTN supports twice the voltage, better for 24 V+ rails or higher-voltage signals. |
| Fet Feature | Logic Level Gate, 1.2 V Drive | Logic Level Gate | UM6K33NTN can fully switch at lower gate drive voltage, useful in low-voltage controllers. |
| Gate Charge (Qg) @ Vgs | Not specified | 2.3 nC @ 5 V | FDC6321C provides gate charge data; 2.3 nC is moderate, important for switching speed and losses. |
| Input Capacitance (Ciss) @ Vds | 25 pF @ 10 V | 50 pF @ 10 V | UM6K33NTN has lower input capacitance, reducing gate drive power and improving switching speed. |
| Mounting Type | Surface Mount | Surface Mount | Both are SMD; no difference here. |
| Operating Temperature Range | up to 150°C (TJ) | -55°C to 150°C (TJ) | FDC6321C rated for wider temperature range, better for harsh environments. |
| Package / Case | 6-TSSOP (UMT6), SC-88, SOT-363 | SOT-23-6 Thin, TSOT-23-6 | FDC6321C’s smaller TSOT-23-6 package reduces board area vs UM6K33NTN’s slightly larger UMT6. |
| Power Dissipation (Max) | 120 mW | 700 mW | FDC6321C can dissipate nearly 6× more power, improving thermal handling. |
| Rds(on) Max @ Id, Vgs | 2.2 Ω @ 200 mA, 4.5 V | 0.45 Ω @ 500 mA, 4.5 V | FDC6321C has significantly lower on-resistance at higher currents, improving conduction losses. |
| Supplier Device Package | UMT6 | SuperSOT™-6 | Different package families; affects footprint and thermal performance. |
| Technology | MOSFET (Metal Oxide) | MOSFET (Metal Oxide) | Both use standard MOSFET tech. |
| Vgs Threshold Max @ Id | 1 V @ 1 mA | 1.5 V @ 250 µA | UM6K33NTN turns on at lower gate voltage, better for low-voltage logic drive. |
Design trade-offs
The UM6K33NTN’s primary strengths lie in its higher voltage rating (50 V) and very low threshold voltage (1 V max at 1 mA), making it well-suited for low-voltage gate drive applications where the supply voltage may be as low as 1.2 V. This is beneficial in battery-powered or low-voltage digital systems, where the MOSFET must switch fully on with minimal gate voltage headroom. Its dual N-channel configuration simplifies designs that only need N-channel switches in a small footprint.
However, its continuous drain current is limited to 200 mA per channel, and its Rds(on) is relatively high at 2.2 Ω, which leads to higher conduction losses and limits its use to low-power switching or signal-level loads. The maximum power dissipation of 120 mW further restricts its thermal capability, requiring careful derating or heat sinking.
The FDC6321C offers a complementary N/P pair, enabling high-side/low-side switch configurations or push-pull stages in a single package. It supports significantly higher currents (680 mA N, 460 mA P) and lower Rds(on) (0.45 Ω @ 500 mA), making it more suitable for loads with moderate power requirements. Its maximum power dissipation of 700 mW allows for better thermal headroom, reducing the chance of thermal shutdown or performance degradation.
The trade-off is the lower maximum drain-source voltage (25 V), limiting its use to lower-voltage rails. Also, the threshold voltage is higher (1.5 V max at 250 µA), which may require a stronger gate drive voltage to fully turn on the device, potentially increasing gate drive losses. The input capacitance is double that of the UM6K33NTN, which can impact switching speed and gate driver power consumption.
From a layout perspective, the FDC6321C’s SuperSOT-6 package is more compact than the UMT6, allowing for reduced PCB area and potentially better thermal dissipation due to smaller package thermal resistance. The dual N-channel UM6K33NTN in UMT6 or SOT-363 variants is slightly larger and may require more board space.
Cost-wise, while pricing is not provided here, typically onsemi’s SuperSOT packaging targets cost-sensitive applications at volume, but the complementary N/P pair integration may add cost compared to a dual N-channel device like the UM6K33NTN. The UM6K33NTN’s advantage in low-voltage gate drive may reduce the need for external gate driver components, saving system cost.
Use-case fit
Choose UM6K33NTN when…
- Your application requires switching at voltages up to 50 V (e.g., automotive 12 V systems with voltage spikes or industrial 24 V rails).
- You need dual N-channel MOSFETs in one package for simple low-side switching or load switching with minimal gate drive voltage (1.2 V logic-level compatible).
- The load current per channel is below 200 mA, such as signal-level switching, level shifting, or small relay drivers.
- Power dissipation is minimal (<120 mW), and thermal management options are limited.
- You prefer lower input capacitance to minimize gate drive losses and speed up switching transitions in low-power systems.
Choose FDC6321C when…
- Your design requires both N and P channel MOSFETs for half-bridge, push-pull, or complementary switching topologies.
- The maximum load current per channel is up to 680 mA (N) and 460 mA (P), such as battery protection circuits, power multiplexing, or load switches.
- Operating voltage is limited to 25 V or less, typical in USB-powered or low-voltage industrial electronics.
- Thermal dissipation up to 700 mW is needed, allowing more headroom for continuous or pulsed higher-current operation.
- Board space is at a premium and you need the smaller SuperSOT-6 package footprint.
- The system can provide at least 4.5 V gate drive to fully enhance the MOSFETs.
Drop-in compatibility
The UM6K33NTN and FDC6321C differ in configuration (dual N-channel vs N/P pair) and package (UMT6 vs SuperSOT-6). They are not pin-compatible or footprint-compatible. The UM6K33NTN uses a 6-TSSOP/SC-88/SOT-363 style package (UMT6), whereas the FDC6321C is in a TSOT-23-6 SuperSOT package with different pin assignments.
Substituting one for the other would require a PCB redesign and schematic changes due to differences in channel types and pinouts. Additionally, gate drive and voltage ratings differ significantly, so the electrical environment must be reevaluated.
Alternatives to consider
- Si2312DS (Vishay) – Dual N-channel MOSFET with low Rds(on) optimized for 20–30 V applications, offering an alternative for low-voltage, moderate-current switching.
- BSS138 (ON Semiconductor) – Single N-channel logic-level MOSFET with low gate threshold, commonly used in level shifting and small-signal switching, though at lower current ratings.
- FDV301N (ON Semiconductor) – Dual N-Channel MOSFET array with low gate charge and Rds(on) for low-voltage, low-current switching applications, similar to UM6K33NTN but with different packaging options.