Here's an update, and I'm also asking for someone to verify one of the conclusions, please see the text in bold below.
As far as I can see, the primary reason for the red LED to start blinking is still the overheating of the battery charging IC, BQ24171; the datasheet describes the STAT output and the status LED on pages 5, 17, 18, 23 and 24. The conditions that cause the battery charging to be suspended because of the battery temperature, and the conditions required to enable or disable the battery charging in general, are described on page 9 and page 18 of the BQ24171 datasheet, respectively.
Another reason for the red LED to start blinking could be that the battery starts to overheat under load, but that doesn't seem plausibe to me, especially because I've never felt that the part of the back cover above the battery becomes even lukewarm.
Here's what the above-described conclusion has been based on:
As an unfortunate result of the first two bullet points, the most power that the PineBook Pro can effectively consume from any of its power inputs, without reaching into discharging the battery, is around 11.4 W (2.6 A at around 2.1 / (100 / (107 + 100)) = 4.37 V, which is the battery voltage when fully charged), despite the fact that the barrel port, for example, can provide 3 A at 5 V, which equals to 15 W. Could anyone, please, use the BQ24171 datasheet and page 11 of the PineBook Pro schematic to verify this and correct me if I'm wrong?
What really s*cks is that the BQ24171 pretty much cannot be made visible to the software, and its configuration is performed using resistors.
This also means that it's impossible to check the current temperature of the battery in software. The only way to communicate with it is to observe the red LED; however, the pin that drives the status LED could be connected to a GPIO line of the RK3399.
Edit: More precisely, the above-stated limit of 11.4 W should be the limit for what the BQ24171 can put into the battery, while the total power draw from one of the two power inputs should be a little higher, due to the losses inside the BQ24171.
As far as I can see, the primary reason for the red LED to start blinking is still the overheating of the battery charging IC, BQ24171; the datasheet describes the STAT output and the status LED on pages 5, 17, 18, 23 and 24. The conditions that cause the battery charging to be suspended because of the battery temperature, and the conditions required to enable or disable the battery charging in general, are described on page 9 and page 18 of the BQ24171 datasheet, respectively.
Another reason for the red LED to start blinking could be that the battery starts to overheat under load, but that doesn't seem plausibe to me, especially because I've never felt that the part of the back cover above the battery becomes even lukewarm.
Here's what the above-described conclusion has been based on:
- As configured in the PineBook Pro, the BQ24171 is nowhere near its charging current limit, which can go up to 4 A, but the battery charging current is configured (using the BQ24171's ISET pin) to stay at or below 3.3 * (20 / (20 + 100)) / 0.2 = 2.6 A. As a result, the BQ24171 isn't running close to its limits.
- The PineBook Pro always takes power from the battery, instead of directly from any of the two power inputs, so no overcurrent protection in the BQ24171 should be taking place, unless the battery is faulty, of course. This pretty much follows the reference design available on page 28 of the BQ24171 datasheet. In other words, the BQ24171 is configured to just keep topping up the battery, and the battery provides additional power even when a charger is plugged into the laptop.
- When the red LED starts blinking, it doesn't return back to solid red until the cooling of the underside of the laptop is improved, nine times out of ten.
As an unfortunate result of the first two bullet points, the most power that the PineBook Pro can effectively consume from any of its power inputs, without reaching into discharging the battery, is around 11.4 W (2.6 A at around 2.1 / (100 / (107 + 100)) = 4.37 V, which is the battery voltage when fully charged), despite the fact that the barrel port, for example, can provide 3 A at 5 V, which equals to 15 W. Could anyone, please, use the BQ24171 datasheet and page 11 of the PineBook Pro schematic to verify this and correct me if I'm wrong?
What really s*cks is that the BQ24171 pretty much cannot be made visible to the software, and its configuration is performed using resistors.
This also means that it's impossible to check the current temperature of the battery in software. The only way to communicate with it is to observe the red LED; however, the pin that drives the status LED could be connected to a GPIO line of the RK3399.Edit: More precisely, the above-stated limit of 11.4 W should be the limit for what the BQ24171 can put into the battery, while the total power draw from one of the two power inputs should be a little higher, due to the losses inside the BQ24171.
