9.2.2.2 Dead Battery Operation

For this application, we want to support 100-W dead battery operation; when the laptop is out of battery, we still want to charge the laptop at 20 V and 5 A. This means that the USB PD Controller must receive power in dead battery mode. The TPS65982 has its own built in LDO in order to supply the TPS65982 power from V_BUS in a dead battery condition. The TPS65982 can also provide power to its flash during this condition through its LDO_3V3 pin.

The OVP FETs of the TPD8S300A remain OFF when it is unpowered in order to insure in a dead battery situation proper protection is still provided to the PD controller in the system, in this case the TPS65982. However, when the OVP FETs are OFF, this isolates the TPS65982s dead battery resistors from the USB Type-C ports CC pins. A USB Type-C power adaptor must see the RD pull-down dead battery resistors on the CC pins or it does not provide power on V_BUS. Since the TPS65982s dead battery resistors are isolated from the USB Type-C connector's CC pins, the built-in, dead battery resistors of the TPD8S300A must be connected. Short the RPD_G1 pin to the C_CC1 pin, and short the RPD_G2 pin to the C_CC2 pin.

Once the power adaptor sees the dead battery resistors of the TPD8S300A, it applies 5 V on the V_BUS pin. This provides power to the TPS65982, turning the PD controller on, and allowing the battery to begin to charge. However, this application requires 100 W charging in dead battery mode, so V_BUS at 20 V and 5 A is required. USB PD negotiation is required to accomplish this, so the TPS65982 needs to be able to communicate on the CC pins. This means the TPD8S300A needs to be turned on in dead battery mode as well so the TPS65982s PD controller can be exposed to the CC lines. To accomplish this, it is critical that the TPD8S300A is powered by the TPS65982s internal LDO, the LDO_3V3 pin. This way, when the TPS65982 receives power on V_BUS, the TPD8S300A is turned on simultaneously.

It is critical that the TPS65982's dead battery resistors are also connected to its CC pins for dead battery operation. Short the TPS65982s RPD_G1 pin to its C_CC1 pin, and its RPD_G2 pin to its C_CC2 pin. It is critical that the TPS65982s dead battery resistors are present; once the TPD8S300A receives power, turns on its OVP FETs and then removes its dead battery RD resistor, TPS65982's RD pull-down resistors must be present on the CC line in order to guarantee the power adaptor stays connected. If RD is not present the power adaptor will eventually interpret this as a disconnect and remove V_BUS.

Also, it is important that the TPS65982's dead battery resistors are present so it properly boots up in dead battery operation with the correct voltages on its CC pins.

Once this process has occurred, the TPS65982 can start negotiating with the power adaptor through USB PD for higher power levels, allowing 100-W operation in dead battery mode.

For more information on the TPD8S300A dead battery operation, see the CC Dead Battery Resistors Integrated for Handling the Dead Battery Use Case in Mobile Devices section of the datasheet.