SDAA050 August   2025 BQ25180 , BQ25186 , BQ25188 , BQ25622E , BQ25638 , BQ25798 , BQ25890 , TPS2121

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Possible Architectures
    1. 2.1 Power Mux
      1. 2.1.1 Other Power Mux Considerations
      2. 2.1.2 Power Mux Over Voltage and Priority Settings
      3. 2.1.3 Power Mux Testing
    2. 2.2 Multicell Charger IC
    3. 2.3 Dual Chargers
    4. 2.4 eFuses (USB OTG)
  6. 3Summary
  7. 4References

2.1 Power Mux

The example presented uses the TPS2121 power mux and the BQ25638 battery charger IC. The circuitry interfacing the two devices is simple: connect the OUT pin of the power mux to the VBUS pins of the battery charger IC.

Power Mux System Diagram Figure 2-1 Power Mux System Diagram

Pay special attention to the input capacitor for the BQ25638. In this application selecting a larger capacitor than is normally selected when the charger IC is connected directly to a power supply can be helpful. This helps hold up the input voltage to the battery charger IC during a power mux switch-over. The BQ25638 data sheet recommends using a 1uF capacitor and this is likely large enough in the case of the TPS2121 which has a fast switch over time of 5us. In contrast, for other power mux ICs such as the TPS2120, which has a 100us switch over time, a larger capacitor must be selected. The particular value must be selected based on the current draw of the specific application and sensitivity to voltage dips. The voltage dip can be found using Equation 1

Equation 1. V D I P = t s w × ( I o u t C o u t )