SLUAAI1 December   2021 BQ25798

 

  1.   Trademarks
  2. 1Introduction
  3. 2Solar Battery Charging with the BQ25798
    1. 2.1 Making Use of FOCV
    2. 2.2 BQ25798 Key Features for MPPT
    3. 2.3 BQ25798 Key Registers
    4. 2.4 BQ25798 MPPT Algorithm
    5. 2.5 Using Charge Current for Algorithm Improvement
    6. 2.6 Second Algorithm in Action
  4. 3Summary
  5. 4References

2.3 BQ25798 Key Registers

The BQ25798 has one key register, REG15, to allow solar panel MPPT. The most important bits relate to the K-factor control and the MPPT enable control. Table 2-1 demonstrates the key bits for MPPT control.

The K-factor control is implemented by the VOC_PCT bits and determines what percentage of the OCV of the solar panel the BQ25798 will set the VINDPM register to. This is crucial to the operation of the panel.

To enable the MPPT, the EN_MPPT bit needs to be checked. The battery has to also be above VSYSMIN to enable MPPT.

In addition, the VOC_RATE bits adjust how often the OCV of the solar panel is measured. The VOC_DLY bits adjust how long the converter turns off when the solar panel OCV is measured.

Table 2-1 REG15 Key Bits for MPPT Control
Name Bits Function
VOC_PCT 7-5 To set the VINDPM as a percentage of the VBUS open circuit voltage when the VOC measurement is done.
EN_MPPT 0 Enable the MPPT to measure the VBUS open circuit voltage.
VOC_RATE 2-1 The time interval between two VBUS open circuit voltage measurements.
VOC_DLY 4-3 After the converter stops switching, the time delay before the VOC is measured.