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

2.1.1 Other Power Mux Considerations

The TPS2121 maximum input voltage and current characteristics meet or exceed those of the BQ25638 meaning that the inclusion of the power mux does not limit any features of the BQ25638. However, at high input currents, such as the 3.2A maximum of the BQ25638, the resistance across the power mux results in a significant voltage drop across the power mux.

Typical and Maximum Resistance values for the TPS2121 and TPS2120 Figure 2-2 Typical and Maximum Resistance values for the TPS2121 and TPS2120

This voltage drop can be of concern in applications using linear or buck only charging ICs (including the BQ25638), where the battery regulation voltage approaches the input voltage. For example, in the common case of a 4.2V Li-ion cell and a 5V USB source there is only a 0.8V of headroom even before considering the impedance of the power source and the dropout voltage required by the charging device.

If lower resistance is required, similar functionality can be accomplished with dual eFuses from TI’s large catalog of eFuses. However, if the full voltage range of the charger IC is not required the TPS2117 power mux with a voltage limit of 5.5V and current limit of 4A can be used. This device has a typical on-resistance of only 20mΩ and a lower cost.