Hi,
Firstly thank you for answering my thread. I have a circuit I want to design and want to verify my values. I have a MOSFET that when turned on will pass 12.5A to the load at Vgs = 10V. According to the datasheet, Rds(on) = 0.0011 for Vgs = 10V. Therefore, the power dissipated is P_diss = I_drain*I_drain*Rds(on) = 0.172W. This a typical operating environment and I think is correct. What I want to do now is determine the junction temperature of the MOSFET at the max ambient temperature of 33C (circuit will be enclosed) and confirm it is operable at that Ta. Attached is the datasheet for the mosfet I am using.
This is what I have calculated using values from the datasheet I think are appropriate (this is where I have trouble understanding).
The following values are from the datasheet and used to make my calculations.
Max Junction Temperature = 150C
Max Thermal Resistance RthJA = 33 C/W
Max Thermal Resistance RthJC = 2.4 C/W
Using On-Resistance vs Junction Temperature Graph Max Rds_ON (Vgs = 10V) = Normalized_Value_Rds_On * Max_Ambient_Temp_Rds_On = 1.125*2.7 = 4.16 ohms
What I have calculated
Max Power Dissipated = 12.5*12.5*4.16 = 650.5W
Estimated Max Junction Temperature = Ta + (Max_Power_Dissipated*RthJC) = 1593.9C
I am having trouble justifying this and doesn't seem to make sense. I used theRthJA instead and got 21495.9C. Which is way crazy! Not sure what I am missing here.
Can someone advise please.
Thank you.
Firstly thank you for answering my thread. I have a circuit I want to design and want to verify my values. I have a MOSFET that when turned on will pass 12.5A to the load at Vgs = 10V. According to the datasheet, Rds(on) = 0.0011 for Vgs = 10V. Therefore, the power dissipated is P_diss = I_drain*I_drain*Rds(on) = 0.172W. This a typical operating environment and I think is correct. What I want to do now is determine the junction temperature of the MOSFET at the max ambient temperature of 33C (circuit will be enclosed) and confirm it is operable at that Ta. Attached is the datasheet for the mosfet I am using.
This is what I have calculated using values from the datasheet I think are appropriate (this is where I have trouble understanding).
The following values are from the datasheet and used to make my calculations.
Max Junction Temperature = 150C
Max Thermal Resistance RthJA = 33 C/W
Max Thermal Resistance RthJC = 2.4 C/W
Using On-Resistance vs Junction Temperature Graph Max Rds_ON (Vgs = 10V) = Normalized_Value_Rds_On * Max_Ambient_Temp_Rds_On = 1.125*2.7 = 4.16 ohms
What I have calculated
Max Power Dissipated = 12.5*12.5*4.16 = 650.5W
Estimated Max Junction Temperature = Ta + (Max_Power_Dissipated*RthJC) = 1593.9C
I am having trouble justifying this and doesn't seem to make sense. I used theRthJA instead and got 21495.9C. Which is way crazy! Not sure what I am missing here.
Can someone advise please.
Thank you.
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