cait-sith
Newbie level 3
N.B. This is my first time designing a real-world circuit with transistors.
The goal is to switch a fully-resistive load in and out of a circuit with a MOSFET switch. The switch shall be controlled with a micro-controller.
Summary of design parameters:
* ID = 1A (max)
* TA = 50 °C (max)
* VGS = 3.0 V (min)
The DMN3404L was chosen as a candidate. It is an N-Channel Logic Level MOSFET. The datasheet is available at: **broken link removed**
From the datasheet, we find:
* VGS_th = 2.0 V (max)
* RDS_on = 28 mΩ (max) at VGS = 10V, TA = 25 °C
* TJ = 150 °C (max)
* RθJA = 90 °C/W
Maximum power dissipation, PD, is:
* PD = (TJ - TA) / RθJA = 1.11 W
Given ID = 1A (max), TA = 50 °C (max):
* RDS_on = PD / ID^2 = 1.11 Ω (max)
So, as long as our RDS_on is < 1.11 Ω, we should be okay. Therefore, we need to calculate RDS_on for our particular VGS.
From Figure 5, we find RDS_on is de-rated by 0.5% / °C above 25 °C. Therefore, for a junction temperature of 150 °C:
* RDS_on = 28 * (1 + 0.005*125) = 46 mΩ (max) at VGS = 10V.
But, we are using VGS = 3V, not 10V. How do I calculate RDS_on (max) when VGS = 3.3V?
The goal is to switch a fully-resistive load in and out of a circuit with a MOSFET switch. The switch shall be controlled with a micro-controller.
Summary of design parameters:
* ID = 1A (max)
* TA = 50 °C (max)
* VGS = 3.0 V (min)
The DMN3404L was chosen as a candidate. It is an N-Channel Logic Level MOSFET. The datasheet is available at: **broken link removed**
From the datasheet, we find:
* VGS_th = 2.0 V (max)
* RDS_on = 28 mΩ (max) at VGS = 10V, TA = 25 °C
* TJ = 150 °C (max)
* RθJA = 90 °C/W
Maximum power dissipation, PD, is:
* PD = (TJ - TA) / RθJA = 1.11 W
Given ID = 1A (max), TA = 50 °C (max):
* RDS_on = PD / ID^2 = 1.11 Ω (max)
So, as long as our RDS_on is < 1.11 Ω, we should be okay. Therefore, we need to calculate RDS_on for our particular VGS.
From Figure 5, we find RDS_on is de-rated by 0.5% / °C above 25 °C. Therefore, for a junction temperature of 150 °C:
* RDS_on = 28 * (1 + 0.005*125) = 46 mΩ (max) at VGS = 10V.
But, we are using VGS = 3V, not 10V. How do I calculate RDS_on (max) when VGS = 3.3V?