Your question seems to be about how to drive N-MOSFETS with signals coming from a 3.3V micro-controller.
Most usually, MOSFET are driven so they’re either ON with a very little resistance between drain and source (noted Rds), or they’re OFF, with an almost infinite Rds. To be ON, a N-MOSFET needs the Gate voltage to be higher than the Source voltage. Voltage between Gate and Source is noted Vgs.
How high Vgs needs to be for a N-MOSFET to turn ON?
- By built, each N-MOSFET has a threshold value, noted Vgsth. If Vgs is below Vgsth, then the N-MOSFET doesn’t let pass any amount of current between Drain and Source. In other words, the resistance Rds is infinite.
- If Vgs is just above threshold, the N-MOSFET is not totally ON. It may let pass some current, but Rds can still be non negligible. In this condition the N-MOSFET would dissipate a lot of power and possibly burn.
The characteristic of Rds and Vgs is to be found in transistor’s data sheet. Often they show the Admittance rather than directly the Rds. This is an example from IXTA80N10T:
The Vgsth of this model is between 2.5V and 4.5V, and it is where the curves starts, but to really turn ON the transistor you better be close to 6V.
This poses an obvious problem when your micro-controller can only output 3.3V, but before solving this, you have to decide if your N-MOSFET is going to be in High Side or Low Side configuration:
Depending on your configuration:
- If the N-MOSFET is placed at Low Side, then you only need to find a way of amplify the 3.3V control signal to a voltage high enough to turn on the N-MOSFET.
- If the N-MOSFET is placed at High Side, then you need a voltage that is higher than the power source.
The circuits to solve these problems are called “Low Side Driver” and “High Side Driver”, respectively:
- The easiest solution is to buy an integrated circuit to perform the task, particularly for the High Side Driver.
- Some integrated circuits contain several High or Low Side Drivers in one package. Some, even, contain one High and one Low.
To correctly select the appropriate High or Low Side driver, pay attention to:
- Maximum voltage rating - 14V is way below breaking point of most of those drivers.
- Logical levels - most are compatible with both 3.3V and 5V.
- Minimum voltage cut off - Some drivers will stop driving if the power source goes below a value.
- Maximum switching frequency - compare it with your requirements.
- Particular points for High Side Drivers:
- Minimum switching frequency - The High Side Driver uses a charge pump to create the higher voltage, but this can only work with some switching.
- Vgs protection - Without specific protection, a High Side Driver will typically produce a Vg that is twice the value of Vcc. In this condition, the Vgs will be as high as Vcc. The maximum rating of Vgs is usually around 20V. So, if your Vcc is above 20V, you need this kind of protection.
There are two families of drivers:
- Gate drivers - Those drive an external transistor, usually a N-MOSFET
- Load drivers - Those have an internal transistor and require less auxiliary circuitry, at the expense of a smaller current rating.
(I haven't checked if any of those examples are appropriate for your particular application)
Also, as Lundin mentions in his comments, "there's a special category referred to as "smart" high side drivers. These have all manner of protection mechanisms built-in, to make them extra rugged (undervoltage, overvoltage, overcurrent, overheat etc). And specifically designed for 12V or 24V applications".