Hi,

In general, when we refer datasheet of dc dc converter (Linear/Switching), the Junction to ambient thermal resistance is mentioned against a JEDEC standard.
Let us consider JEDEC standard 51-7.
It mentions Board Dimension (if package length is less than 27 mm) 76.20 mm x 114.3 mm.
It also mentions the other parameters and values.
If I use a PCB of lesser size (Eg: 30 mm x 40mm), what could be the value of Θj-a? Will it be same?
How do I scale it?