Temperature Coefficient of MOSFET

[navbp]

The resistance of a conductor at temperature T can be calculated by

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

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

R_DSon(Tj) = R_DSon(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?

Thank you in advance!
Regards.

 

[FvM]

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.