keywords: Power MOSFET series gate resistor value, Power MOSFET series resistor power requirement, Power MOSFET Driver calculation

### The Objectives

This is a simple, but very useful calculator to estimate:

- MOSFET gate current,
iG [A]. - Time that the MOSFET will turn on,
tON [us]. - The resistor (
RG2 ) value that must be added to the MOSFET gate and achieve the above two estimations [Ohm] - The average power (
Pave ) which must be endured byRG2 . This value must be employed instead of the pulse power.RG2 will limit the power delivered by the MOSFET driver which can be tuned to limittON .

### 1 Metal Oxide Semiconductor Field Effect Transistors (MOSFET)

MOSFETs need to be matched to the power requirements with a factor of safety (FoS) of at least 1.2 for both currents and voltages. You will encounter two types of channels, N and P{channel; P-channel MOSFETs are rarely used and thus, you will have to go with the N-channels. N-channel MOSFETs have the advantage of having less conduction losses owing to the fact that they employ electron-based minority carriers which are much more efficient than the hole-based minority carriers of the P-channel ones.

#### 1.1 Important MOSFET parameters

The important parameters which will be employed in later sections are:

Normally found at the maximum ratings section, this is the gate-source voltage range; it may range from 10 to 20V. | |

A dynamic characteristic which is the total charge of the MOSFET’s gate [nC]. It can be employed to estimate the instantaneous current needed to turn on a MOSFET in a specied time. | |

This is a design parameter to maximize or minimize the worst case input gate current [ns]. | |

This is the internal gate resistance of the MOSFET. We will use this fixed resistance to calculate an additional resistor to limit the gate current, |

#### 1.2 Gate current equations

**The iG is necessary in order to calculate the wire diameters/material or PCB widths.**

1.3 MOSFET driver | RG2 equation

1.4 Power determination of the RG2

2 Putting all the equations to work! MOSFET iG , RG2 and power calculation example

In this section,the following design parameters are employed:

From the IPB083N10N G N-channel MOSFET from Infineon:

Please note that this current will only be applied to the first 500[ns] needed to turn on the MOSFET, after that, a very small current will be needed to maintain the MOSFET ON because MOSFETs are voltage-driven. Of course, smaller

In this example, we will use a 100 [ohm] resistor. Therefore, the new gate current is calculated by rearranging eqn. (2):

And the new time to turn on the MOSFET is, after rearranging eqn. (1):

In this case, a resistor with a rated power of 1/4 [W] will be chosen, which is well above the average power.

**Edit: VBS will be employed instead of VGS if you are using a bootstrap IC. VBS is the MOSFET driver’s effective voltage to turn on the MOSFET. VBS is equal to the driving voltage of the bootstrap IC minus the voltage drop of the Bootstrap diode.**