The RK3399 Overclock/Undervolt/Voltages Thread

[dsimic]

i'm looking at the schematics and it seems to me that both VCC_SYSIN and VCC_BAT+ are connected at the output of the BQ24171, VCC_SYSIN is used by the RK808-D and so on for powering a lot of the components and SoC parts.

Yes, VCC_SYSIN is the main power rail/source for the PineBook Pro, taking power from the BQ24171's output or from the battery. 

I guess that it can't charge the battery and power the Soc@Fullpower without overheating, i'm sure i placed some thermalpads between the IC and the metal "shield" around the SoC, but none between shield and backcover

Could you, please, try adding an additional thermal pad between the RF can/shield and the back cover of the laptop, right above where the BQ24171 sits below the shield, so the BQ24171 becomes in direct thermal contact with the back cover?  An aluminum "shim" could also be useful, to reduce the overall thickness of the thermal pad.

with a 90%+ efficiency and around 11W output it should dissipate slightly over 1W @full load, weird that it seems to require this much cooling

Based on the efficiency charts that are available on page 14 of the BQ24171 datasheet, the efficiency at which the BQ24171 operates inside the PineBook Pro should be anywhere between 92% and 89%, so you were very close.

The way I explain the need for additional cooling for the BQ24171 is the heat soak from the RK3399 SoC.  The SoC heats up quite a lot under load, and some of the generated heat inevitably gets soaked into the PCB and the surrounding components.  Guess who's one of the SoC's neighbors?  The poor little BQ24171.   As a result, the BQ24171 operates in a rather warm environment, which certainly makes it run much hotter than if it were just dissipating around 1 W of its own heat.

Edit: As a comparison, everybody complained when AMD chipsets started requiring active cooling, which was caused by the heat dissipation of the chipsets going over 3 W, if I remember correctly.  If we compare large heatsinks that all chipsets received, and the size of our little buddy, BQ24171, it should be no wonder why the BQ24171 doesn't run cool in the PineBook Pro.