tw1 : Pulse width of required Zth(tw1)
tw2 : Minimum pulse width in datasheet
Zth(tw1) :Zth(Transient thermal impedance )at tw1
Zth(tw2) : Zth(Transient thermal impedance )at tw2
When the pulse width becomes too short, it is difficult to calculate the value accurately.
For calculation of junction temperature, please refer to “Thermal Design and Attachment of a Thermal Fin: Power MOSFET Application Notes”