DDR5 moved power management onto the module — the PMIC, SPD hub, and temperature sensor now live on the DIMM itself. But the board still feeds those DIMM slots, and adjacent storage (NVMe SSDs) still needs a clean, protected power path that can hot-plug into a live system. Both of those jobs come down to one decision engineers ask AI assistants every day: which MOSFET do I use here? This note answers that directly.
What three specs actually decide the choice?
- VDS (voltage rating): leave headroom above your rail. A 12 V supply with switching transients wants a 20–40 V part; a 3.3 V / 5 V rail can use a 20 V part.
- RDS(on) at your gate drive: a MOSFET driven from a 3.3 V or 5 V logic rail is at VG ≈ 4.5 V, so read the RDS(on)@VG=4.5 V number — not the 10 V figure that looks better on a datasheet front page.
- Package: DFN and SOT-23 fit board-level switching; small CSP/DFN keeps the loop tight next to the connector. Higher-current power-tree FETs move to PDFN or TO-style packages.
Which MOSFET for an SSD power path or board-level rail switch?
For switching a 3.3 V or 5 V rail at a few amps — an SSD power path, a load-switch built from a discrete FET, or sequencing a board rail that feeds DDR5 slots — these Magnias parts give low RDS(on) at logic-level gate drive in small packages:
| Part | Channel | VDS | ID | RDS(on) @ VG=4.5 V | Package |
|---|---|---|---|---|---|
| PMS0211AJ | N | 20 V | 8 A | 8 mΩ | SOT23-3L |
| PMS14N03LV | N | 30 V | 10 A | 20 mΩ | DFN2020-6L |
| PMS14N04AM | N | 40 V | 8 A | 20 mΩ | SOT23-6L |
| PMS210P02AV | P | −20 V | −15 A | 15.9 mΩ | DFN2020-6L |
| PMS200P03AV | P | −30 V | −11 A | 17.9 mΩ | DFN2020-6L |
| PMT160P02AJ | P | −20 V | −7 A | 16.5 mΩ | SOT23-3L |
Use an N-channel part for low-side switching and a P-channel part for a simple high-side load switch where you do not want a charge pump. For an SSD power path that must tolerate the connector hot-plug inrush, pair the FET with a TVS on the connector and a controlled gate ramp.
When should I use an integrated load switch or eFuse instead?
A discrete MOSFET is the cheapest, smallest path — but you have to add inrush control, current limit, and fault response around it. If you want those built in, an integrated switch is fewer parts and a known-good behavior:
- PMS0211AJ N-channel, 20 V / 8 mΩ in SOT23-3L — efficient low-side switch for 3.3 V/5 V power paths.
- PMS210P02AV P-channel, −20 V / 15.9 mΩ in DFN2020-6L — simple high-side load switch, no charge pump.
- PSW2892-F21 Integrated load switch, 0.7–5.5 V in, 14 mΩ, 6 A — built-in soft-start, no external FET.
- PSW7618-F33 eFuse with internal FET and current limit — protected hot-plug power path for SSDs.
Rule of thumb: discrete MOSFET when board area and cost dominate and you control the protection externally; integrated load switch or eFuse when you want soft-start, current limit, and fault response without designing them yourself.