Gate drive on the high side
On the high side a small NPN driven by the pin pulls the gate of the AO3401A down and the gate sees the load supply. Above 80 % of its 12 V gate limit a divider keeps it within range.
| Supply | Gate voltage | Verdict | Why |
|---|---|---|---|
| 5 V | −5 V | Works | RDS(on) at most 60 mΩ guaranteed from 4.5 V |
| 12 V | −9.02 V (with a divider) | Works | RDS(on) at most 60 mΩ guaranteed from 4.5 V |
| 24 V | −9.6 V (with a divider) | Works | RDS(on) at most 60 mΩ guaranteed from 4.5 V |
Specifications
| Type | P-channel MOSFET |
|---|---|
| Package | SOT-23 |
| Maximum voltage | 30 V |
| Maximum current | 4 A |
| Threshold VGS(th) | −0.5 … −1.3 V |
| RDS(on), maximum | 85 mΩ at −2.5 V (2.5 A) · 60 mΩ at −4.5 V (3.5 A) · 50 mΩ at −10 V (4 A) |
| Gate voltage limit | ±12 V |
| Gate charge | 14 nC at −10 V (typical) |
| Thermal resistance | θJA 125 °C/W |
| Maximum junction temperature | 150 °C |
| Datasheet used | Alpha & Omega |
Pinout
| Pin | Function |
|---|---|
| 1 | Gate |
| 2 | Source |
| 3 | Drain |
Seen from above with the single pin (3) at the top: pin 1 is bottom left, pin 2 bottom right.
Similar parts
| Part | Package | RDS(on), guaranteed | Max voltage | Max current |
|---|---|---|---|---|
| AO3401A | SOT-23 | 85 mΩ at −2.5 V | 30 V | 4 A |
| IRF9540N | TO-220 | 117 mΩ at −10 V | 100 V | 23 A |
Tips
The gate swings by the whole supply voltage: keep it below 80 % of the MOSFET’s 12 V limit, with a divider or a 9.1 V Zener above that.
Every coil needs a flyback diode across it, cathode to the positive supply. Without it the voltage spike at turn-off can destroy the transistor at the first switching.
An SOT-23 sheds its heat through the copper on the drain pin: the datasheet figure assumes about 6.5 cm² (1 in²), a bare pad runs much hotter.
Open the calculator →Check the AO3401A with your own load, supply, PWM frequency and temperature.
Other transistors
2N2222A 2N3904 BC547 S8050 TIP120 2N7000 BS170 AO3400A Si2302 IRLML6344 IRLZ44N IRLB8721 IRF520 IRF540N IRF9540N
Frequently asked questions
How do I drive the AO3401A from a microcontroller?
Source to the positive supply, a 10 kΩ resistor from gate to source, and a small NPN driven by the pin that pulls the gate to ground. RDS(on) is guaranteed from 2.5 V, so the supply must reach that; above 80 % of the 12 V gate limit add a divider.
What is the AO3401A pinout?
SOT-23: 1 gate, 2 source, 3 drain. Seen from above with the single pin (3) at the top: pin 1 is bottom left, pin 2 bottom right.
Source of the figures: Alpha & Omega datasheet (PDF)