Other Parts Discussed in Thread: MSP430F5419A
We have a design that uses the BQ24650 to charge a 13.8V, 10Ah LiPo battery. The problem is that when the system is powered from a solar panel, the battery charging starts immediately and causes motorboating. This is because the solar panel is not able to supply enough current AND the microcontroller (which sets MPP voltage, enable/disable charging etc.) doesn't have time to turn on to control the system.
So obviously we need a way to disable charging until the MCU can turn on. The optimal way would be to pull MPPSET to zero for a short time to allow the MCU to start. On the MPPSET pin we have a voltage divider of 523k connected to Vin, 47k to GND; and this has a 100nF cap to GND plus a 18pF cap to Vin. In this case Vin is the system input voltage, e.g. from the solar panel.
Question: What are the ramifications if I change the 100nF cap to 1uF? That would increase the MPPSET turn on time from 20mSec to 100mSec (according to simulation) which should allow the MCU to startup and disable charging until we can determine optimal MPP setting. The only downside that I could foresee is that this makes the system slower to change MPP tracking during a change in Vin. However, the timeframe we're talking about (100mSec) is still very fast compared to the speed of clouds across a solar panel. Are there any other downsides?