# Temperature Coefficient of MOSFET

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#### navbp

##### Newbie level 6
The resistance of a conductor at temperature T can be calculated by

R(T) = R(To)*{1 + alpha*(T-To)}

Where R(T), R(To) = Resistance at temperature T, To
alpha = Temperature coefficient of conductor
T, To = Temperatures

But in an Infineon application note "MOSFET Power Losses Calculation Using the Data-Sheet Parameters", the relationship of RDSon of MOSFET at temperature Tj is given by

RDSon(Tj) = RDSon(25C)*{1+(alpha/100)}(Tj-25C)

Could somebody please explain why there is a difference?
What is the unit of alpha in the second formula?

Regards.

#### FvM

##### Super Moderator
Staff member
The resistance of a conductor at temperature T can be calculated by

R(T) = R(To)*{1 + alpha*(T-To)}
should be completed like "if the conductor exposes a linear temperature coefficient".

But silicon rather shows an exponential TK, as modelled by the given expression. The alpha unit is percent per K, the characteristic is quite similar to your linear expression around 25° C (except for the factor 100), due to the constant relative slope the absolute slope increases with rising temperatures.

navbp

### navbp

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