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TPS25750: Can it negotiate power as a sink device with no battery?

Part Number: TPS25750


Typically when a depleted sink device is plugged into a USB PD charger, it has dead battery resistor (Rd-DB) to trigger the charger to provide power until its internal battery is charged enough, then it replaces Rd-DB with "regular" Rd to negotiate a PD contract.

For sink devices with no internal battery, I am concern that the delay that occurred during the switch from Rd-DB to Rd will cause the PD charger to stop providing power and cause a power cycle issue:

  1. Charger provides power to sink controller due to present of dead battery
  2. Sink controller sees power, removes/replaces dead battery resistor
  3. Charger doesn't see dead battery resistor, stop providing power
  4. Since there is no internal battery, sink controller loses power temporarily when switching from dead battery mode to normal mode
  5. Repeat steps 1-4

We've seen some DRP controllers that have this power cycling/oscillating effect.

Does TPS25750 have this effect? Can the TPS25750 be the sink controller for a device with no battery? Is there a delay during the switch from Rd-DB to Rd for TPS25750?


  • Hi Jonathan,

    The expert on this device is on PTO, let me forward to someone that might be able to help.

  • Hi Jonathan,

    No this will not be an issue when booting from a dead battery configuration. I will outline the flow for a dead battery scenario when the TPS25750 is configured for the AlwaysEnableSink configuration and an external EEPROM is connected to the TPS25750

    1. System starts in a "dead battery" condition where this no power being applied to the system and VIN_3V3 of the TPS25750 is not powered
    2. A Type-C charger is connected to the system
    3. The TPS25750 presents an Rd on the CC pin, negotiating an implicit 5V contract with the connected Type-C charger
    4. 5V is presented on VBUS and the TPS25750 boots up from the power presented on VBUS
    5. LDO_3V3 from the TPS25750 goes high, powering the external EEPROM, allowing for the PD controller to load the configuration
    6. Once configuration is loaded, TPS25750 is able to negotiate a PD contract, lets say 20V, with the connected Type-C charger
    7. 20V contract is negotiated and VBUS ramps to 20V

    Throughout this whole procedure VBUS does not drop removing power to the system. Hope this helps answer your question