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TPS25751EVM: TPS25751D - Verify Liquid detection in only Sink Mode.

Part Number: TPS25751EVM

Hi Team,

We are using the TPS25751DREFR chipset for our power delivery application in sink mode only with a max 20V @ 5A supply. We also added a liquid detection feature in our design. Our design operates on an external source with very low internal battery capacity. So we required a minimum quiescent current during battery-operated mode.

PD will support external VIN_3V3 supply input when an external source is not present in VBUS. Since we are using only sink functionality, we removed JP13 from EVK and tested it, and it's working as expected with MCU (EEPROM is not connected).

Now we also require liquid detection functionality. I understand that PD will detect liquidonly when it is powered ON. In a normal use case, when there is no external supply present at VBUS, the PD will be powered OFF because the supply is not provided at the VIN_3V3 pin.

When liquid is present on the Type C port & we insert the Type C adapter, how will the chip behave? 
For example, when type C is applied, PD will power on with a 5V supply. The MCU will boot from a 5V supply and program PD for 20V negotiation and liquid detection. Once the PD program is running, it will check for liquid detection. Since liquid is detected in the Type C port, PD will close the internal switch for its output (MCU supply). 

Now after how much time duration will PD check again for liquid detection? Also, in our application liquid detection is only done after powering the PD; for some time liquid is present in the type C port with supply. So there are chances that it might damage the PD chipset or other sections in the boards as well, like the regulator and MCU.

Can you please confirm the actual scenario for this case? Also in our application, please confirm that we can use liquid detection withoutany damage in PD or other sections.

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  • Hi, 

    A team member will get back to you shortly, thank you for your patience! 

  • Hello,

    When liquid is present on the Type C port & we insert the Type C adapter, how will the chip behave? 

    The PD controller will use the VBUS to boot (powering LDO_3V3) and load the configuration from EEPROM.  In the configuration the GPIO and liquid detection settings are applied and at this time if liquid is present then the PD controller behavior will depend upon if the mitigation and/or interrupt is enabled.  If the mitigation is enabled then the PD controller will disconnect (cc terminations removed) and the far end is expected to stop providing VBUS. When the VBUS is removed the PD controller will reset and the Rd resistors will be presented and the sequence would repeat infinitely until the liquid is removed.

    Alternatively the mitigation can be disabled and an interrupt provided to the host to indicate liquid is present and the host can decide the appropriate action.

    Now after how much time duration will PD check again for liquid detection?

    The PD will check liquid detection continuously while enabled.   The thresholds determine when the liquid is present and when it is removed. 

    Can you please confirm the actual scenario for this case? Also in our application, please confirm that we can use liquid detection withoutany damage in PD or other sections.

    Please be sure to use a protection device so that the SBU pins do not get exposed to a voltage larger than the abs max ratings.

    https://www.ti.com/lit/ds/symlink/tps25751.pdf#page=51

     TPS25751: Liquid detection evaluation 

     TPS25751: Liquid detection sensitivity 

    Regards,
    Chris