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TPS25751: Current flow during sink and source modes

Shwetanshu Singh
Prodigy 170 points
Part Number: TPS25751
Other Parts Discussed in Thread: BQ25756

Tool/software:

Hi,

I want to understand the current flow when the IC is in source and sink modes, respectively. Specifically where is the power drawn from during the two modes.

Thanks

  • 0
    TI__Mastermind 20477 points

    Hi Shwetanshu, 

    Thank you for reaching out!

    The TPS25751 features an internal sourcing power path (PP5V) in which the current flows from PP5V (5V input) to VBUS. When the device is sinking, current flows from VBUS to PPHV. PPHV is a bidirectional power path, and when paired with an external DCDC, can also be used to source >5V.

    See section 8.3.2 Power Management in the datasheet for more information. 

     

    Please let me know if you have additional questions. 

    Best Regards, 

    Aya Khedr

  • 0 in reply to Aya Khedr
    Prodigy 170 points

    Hi Aya,

    Thanks for your response. For my application I am using the IC with BQ25756, similar to https://www.ti.com/tool/PMP41062. As I understand it, there are two power profiles. One to power up the IC and the other that flows between type c port to the battery to charge the battery (IC as sink) or to charge a load (IC as source).

    I will present 2 cases.
    1. IC as source (Battery supplies power to Type C connector):  
        - Power from battery is converted to 5V and 3.3V, these are supplied to the TPS25751 IC at PP5V and VIN_3V3 respectively. PP5V powers up VBUS. If VIN_3V3 is not available, the device goes into dead battery mode and power is VBUS is used to power up the IC.

        - Power from battery goes to type C port and BQ25756 supplies voltage as per TPS25751 IC and supplied to load.

    2. IC as sink (Battery is charging from power at Type C connector):
       - VBUS from the Type C connector is supplied to the IC, IC starts in dead battery mode and powers up the PPHV rail. (Is the battery power used to power up the IC in this also??)
       - Power received from type C port is converted by BQ25756 as per TPS25751 IC and supplied to battery.

    Is my understanding correct?

    If I am correct, can any one of these be done:
    1. use a MOSFET to cut off supply at VIN_3V3 (and thus switch off the IC) when nothing is connected at type c port, irrespective of the IC being in sink or source mode. This is to reduce the sleep mode current.

    2.  if a load is connected at the port, that is IC in source mode, disconnect the battery such that it is not supplying any power to the load (to prevent the discharge of the battery beyond a certain level). But it does not affect the functionality when IC is in sink mode, that is battery is charging.

    Thanks

  • 0 in reply to Shwetanshu Singh
    TI__Mastermind 20477 points

    Hi Shwetanshu, 

    Thank you for the detailed response. I will review and get back to you by Wednesday. 

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Prodigy 170 points

    Hi Aya,

    Please update.

  • 0 in reply to Shwetanshu Singh
    TI__Mastermind 20477 points

    Hi Shwetanshu, 

    See my feedback below:

    1. IC as Source

    Shwetanshu Singh said:
    - Power from battery is converted to 5V and 3.3V, these are supplied to the TPS25751 IC at PP5V and VIN_3V3 respectively. PP5V powers up VBUS.

    Your understanding is correct. 

    Shwetanshu Singh said:
    If VIN_3V3 is not available, the device goes into dead battery mode and power is VBUS is used to power up the IC.

    To clarify, the TPS25751 does support dead-battery start-up when VIN3V3 is unavailable and power is available on VBUS. This scenario is when the device is behaving as a sink, not source. 

    2. IC as Sink

    Shwetanshu Singh said:
     - VBUS from the Type C connector is supplied to the IC, IC starts in dead battery mode and powers up the PPHV rail. (Is the battery power used to power up the IC in this also??)

    As mentioned above, if the device is only powered from VBUS (i.e. powered from the source port-partner), then it would be in a dead-battery state. When powering from a VBUS input, the voltage on VBUS is stepped down through an LDO to LDO_3V3 (see image below from datasheet)

    -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

    Shwetanshu Singh said:
    1. use a MOSFET to cut off supply at VIN_3V3 (and thus switch off the IC) when nothing is connected at type c port, irrespective of the IC being in sink or source mode. This is to reduce the sleep mode current.

    This should be fine. I recommend testing this implementation to ensure proper behavior when device boots up. 

    Shwetanshu Singh said:
     if a load is connected at the port, that is IC in source mode, disconnect the battery such that it is not supplying any power to the load (to prevent the discharge of the battery beyond a certain level). But it does not affect the functionality when IC is in sink mode, that is battery is charging.

    You could also issue a 4CC command to the PD controller to swap power roles when desired. For instance, if the IC is in source mode and the battery discharges to a certain level, you can then swap to sink and the device connected will start sourcing if applicable. 

    Best Regards, 

    Aya Khedr