Because the TPS25750EVM does not ship with a battery, a 12-V buck converter is used to simulate a 3S battery pack connected to the BQ25731RSN. This allows the customer to evaluate the performance of this EVM without having to supply their own 3S battery. The 12 V is generated by the TPS56637 buck converter which is powered from the 20-V DC barrel jack. When configured to use the on board buck converter, the EVM’s source capabilities are limited to 60 watts. An external battery/power supply can be connected to the EVM if more sourcing power is required (up to 100 watts) or if the customer needs to test the charging capabilities of the BQ device. To connect an external battery, remove the jumper J5 first and then connect the battery + terminal to the TP3 test point. It is important to note that in order to charge and external battery, the diodes D2 and D3 will need to be removed or shorted, so that current will not back flow the battery.

Figure 2-2 BQ Charger Partial Schematic