The TPS65988 supports booting from no-battery or dead-battery conditions by receiving power from VBUS. Type-C USB ports require a sink to present Rd on the CC pin before a USB Type-C source provides a voltage on VBUS. TPS65988 hardware is configured to present this Rd during a dead-battery or no-battery condition. Additional circuitry provides a mechanism to turn off this Rd once the device no longer requires power from VBUS. Figure 8-16 shows the configuration of the C_CCn pins, and elaborates on the basic cable plug and orientation detection block shown in Figure 8-14. A resistance R_RPD is connected to the gate of the pull-down FET on each C_CCn pin. During normal operation when configured as a sink, RD is RD_CC; however, while dead-battery or no-battery conditions exist, the resistance is un-trimmed and is RD_DB. When RD_DB is presented during dead-battery or no-battery, application code switches to RD_CC.

Figure 8-16 Dead Battery Pull-Down Resistor

In this case, the gate driver for the pull-down FET is Hi-Z at its output. When an external connection pulls up on C_CCn (the case when connected to a DFP advertising with a pull-up resistance Rp or pull-up current), the connection through R_RPD pulls up on the FET gate turning on the pull-down through RD_DB. In this condition, the C_CCn pin acts as a clamp VTH_DB in series with the resistance RD_DB.