There is no guarantee for that, but usually 5850U is used in ultra-thin laptops and they don't have enough cooling for more than 15W... For example, CPU in Thin

There is no guarantee for that, but usually 5850U is used in ultra-thin laptops and they don't have enough cooling for more than 15W... For example, CPU in Thinkpad X1 Extreme GEN 4 is limited 27 WATT (at least models without vapor chamber) and it's a laptop with quite a good cooling and larger size.