SLYY225 December   2023 BQ25756

 

  1.   1
  2.   Overview
  3.   At a glance
  4.   Battery charging for new USB-C applications
  5.   Optimizing the charging and discharging of portable power stations
  6.   Battery charging for solar applications
  7.   Diversifying battery-charger applications
  8.   Conclusion
  9.   References

Diversifying battery-charger applications

Again, there are many battery-charger design challenges associated with the growth of USB PD and portable backup power; however, the BQ25756 buck-boost battery-charge controller can help address each challenge, specifically because it has these three features:

  • Up to 70-V support on the input and output.
  • Bidirectional power flow.
  • An autonomous MPPT algorithm.

The 70-V support on the input supports the full USB PD voltage range, and the buck-boost controller topology enables any USB Type-C input regardless of the battery voltage, since the device will automatically switch between buck and boost modes depending on the values of VIN and VBATT. The 70-V support on the output allows the BQ25756 to charge up to 14 Li-ion series cells and up to 16 Li-ion phosphate cells.

Bidirectional power flow enables charger system designs that charge and discharge the battery pack with the same USB Type-C port. The BQ25756 can buck and boost in the reverse direction for discharging from the battery pack, regardless if the VOUT in reverse mode is smaller or greater than the battery pack voltage. This feature allows consumers to charge accessories such as laptops and speakers from battery packs for products such as portable power stations and e-bikes using the USB Type-C port.

The BQ25756 comes with MPPT for solar charging applications, with three improvements:

  • Autonomous start.
  • A full VIN sweep.
  • A perturb and observe feature.

The autonomous MPPT can run with default settings, or you can customize features of the MPPT with I2C, such as the time between MPPT algorithm cycles. Once the MPPT algorithm ends, the timer restarts and begins a new cycle once the time you have chosen runs out. During the algorithm, the charger does a global sweep of the VIN to find the absolute MPP. As shown in Figure 8, having multiple solar panels in series or in parallel can result in multiple peaks that you can choose as the MPP. In order to find the true MPP, the algorithm must traverse every peak. The BQ25756 sweeps all of the VIN values to find the maximum MPP, even if there is more than one peak.

GUID-20231114-SS0I-VXRQ-K6FC-SR34XPBS2QRW-low.png Figure 8 Solar-cell curves with more than one peak.