SLVSDC2C February 2016 – August 2021 TPS65981
PRODUCTION DATA
The Type-C port in this design supports the 4 standard discrete source voltages in USB PD (5 V, 9 V, 15 V, and 20 V) by adding the LM3489 DC-DC hysteretic PFET buck controller with GPIOs controlled by the TPS65981 that enables the LM3489 and modifies the output voltage that is supplied to VBUS through the internal PP_HV power switch. In Figure 10-3, the enabled (EN) pin of the LM3489 is controlled by DBG_CTL1 which is mapped to the Plug Event GPIO so that whenever a Type-C plug occurs the voltage regulator will generate the 5-V default output voltage for sourcing Type-C and PDO1 power. The default voltage is set by a resistor divider (RFB1 and RFB2) with the center tap connected to the feedback pin (FB) of the LM3489. The TPS65981 modifies the output voltage when a high voltage PD contract is negotiated by forcing a GPIO output high and switching in a third resistor in parallel with RFB2 in the feedback circuit. In Figure 10-3, GPIO6 indicates a 9-V PD contract (PDO2), GPIO7 indicates a 15-V contract (PDO3), and GPIO8 indicates a 20-V contract (PDO4). The LM3489 was selected because the architecture allows 100% duty-cycle operation, where the only additional power loss in the system is from the RDS,ON of the PFET used in the regulator circuit.