SLUSDV2A May 2020 – May 2021 BQ25798
The device implements a simple algorithm to track the maximum power point (MPP) when the input source is a solar panel. The I-V and P-V curves of a solar panel are most strongly dependent on irradiation and temperature. The MPP is most commonly located between 70%~90% of the Open Circuit Voltage (VOC) of the solar panel. The algorithm automatically and periodically detects the charger input source VOC, and sets the VINDPM to be a ratio of the measured VOC. It is recommended to set the charging current to the maximum value, so that the VINDPM is always triggered and activated. The MPPT algorithm is disabled by default at POR (EN_MPPT = 0). The algorithm runs automatically when EN_MPPT bit is set to 1.
Similar to the FORCE_VINDPM_DET feature, when the battery voltage is lower than VSYSMIN (VSYS_STAT = 1), the MPPT algorithm can not be enabled. The EN_MPPT bit will be reset back to 0 if it is written to 1. In the MPPT process, the buck-boost charger stops switching and keeps in the non-switching status for a time period programmed by VOC_DLY[1:0]. When the charger stops switching, the system is powered by the battery discharging. Then the charger measures the open-circuit voltage of the input soruce attached at VBUS and updates the VINDPM to be VOC_PCT[2:0]*VOC. The converter starts up again for the VOC_RATE[1:0] time interval, stops switching for another VOC_DLY[1:0], measures VOC, and updates the VINDPM register to complete the next cycle. When VBUS goes below VBUS_PRESENT, the EN_MPPT bit will be reset to 0, and forced to be 0 even if the host writes it to 1.
For the EN_ICO, FORCE_VINDPM_DET and EN_MPPT three register bits, only one of them can be set to 1 at a given time. If one of them is enabled, the charger will block the host from enabling the other two features until the first is disabled.