SLYY195A August   2020  – May 2022 BQ25790 , BQ25792 , BQ25798

 

  1.   At a glance
  2.   Authors
  3.   3
  4.   Why universal charging
  5.   On-the-go charging
  6.   Integrated components maximize power density
  7.   Implementing buck-boost charging
  8.   Conclusion
  9.   References

Why universal charging

One critical benefit of the widespread adoption of USB Type-C is a realistic path to a universal adapter and corresponding e-waste reduction. Although the USB Type-C connector is unified, adapter power ratings and voltages still have large variations, including the legacy 5-V USB adapter and USB PD adapters capable of providing a voltage range from 5 V to 20 V. In addition, different portable devices might have different numbers of cell batteries inside. These variabilities in input voltage and battery voltage require a buck-boost topology for battery-charger integrated circuits (ICs).

Figure 1 shows a system block diagram for a USBPD charging solution. Through the CC1/CC2 pins, the USB PD controller identifies the adapter. After handshaking between the adapter and the USB PD controller, the unit managing the charging power path turns on back-to-back MOSFETs to pass the adapter voltage from VBUS to the input of the buck-boost charger. This unit (U1) also has to provide overvoltage and overcurrent protection by sensing the input voltage and current through the sensing resistor. The buck-boost charger requires four switching MOSFETs to step the input voltage up or down in order to charge the different battery voltages. In addition, the narrow VDC (NVDC) power path management and charging current sensing require one more MOSFET and another current-sensing resistor at the charger’s output side.