Why is my phone (S7) constantly at 30 C when wireless charging?

[AC Question]

I have a Samsung S7 and i got an Itian wireless charging, supposed to support Qi standards.

When i wireless charge overnight, my phone stays warm at 30 C the whole night, as i can see in GSAM battery tool. After i pick it up from the wireless charger it cools down.

I've read other people saying that wireless chargers turns off when the battery is at 100%, i am not sure it is my case. Any ideas about what can be the cause of this heat ?

Thanks