A typical design is shown in Figure 10-1. This design uses the BQ25122 with external resistors for ILIM, IPRETERM, and ISET. These are not needed if these values are set with a host controller through I²C commands. This design also shows the TS resistors, which is also optional.

When powering up in default mode the battery voltage is the default for the part (4.2 V), the SYS output is the default (1.8 V). External resistors set the charge current to 40 mA, the termination current to 10% (4 mA), and the input current limit to 100 mA. If the I²C interface is used the part goes to the internal default settings until changed by the host.