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Original question:

TPS25750: Is there any criteria to select TPS25750D or TPS25750S?

TPS25750: external MCU requirement on BQ25731 scenario

Serkan Erboral
Prodigy 20 points
Part Number: TPS25750
Other Parts Discussed in Thread: BQ25731, BQ25792, ,

Hi Team,

I have questions regarding purposed block diagram shown below.

1. TPS25750S GUI has support for BQ25731 device so using this system standalone (without any MCU) should be possible? The article "e2e.ti.com/.../adding-usb-type-c-with-power-delivery-to-battery-powered-applications-smaller-faster-fewer-components" tells using an external MCU in BQ25731 system as mandatory. What am I missing?

2. Is it possible to add an external input source of 26V as shown in diagram?

3. Usage of BQ25792 is not recommended for applications above 45W. Does this limit comes from the internal mosfets of buck boost converter? Sourcing a 45W system means the possibility of doubling the input current as it is the sum of the charging power and system power so a power requirement of 90W on the Buck boost converter. If the system works only with battery power (I mean no charging simultaneously) then using BQ25792 over 45W scenarios is also possible, right?

Could you help me clarifying this issues? Thank you in advance.

  • +1
    TI__Mastermind 31400 points

    Hi Serkan,

    Serkan Erboral said:
    1. TPS25750S GUI has support for BQ25731 device so using this system standalone (without any MCU) should be possible? The article "e2e.ti.com/.../adding-usb-type-c-with-power-delivery-to-battery-powered-applications-smaller-faster-fewer-components" tells using an external MCU in BQ25731 system as mandatory. What am I missing?

    TPS25750 can support BQ25731 without MCU. Our TPS25750EVM uses TPS25750 + BQ25731 without MCU.

    Maybe I missed it but I did not find where in the article stated that external MCU is mandatory. Can you point me towards it?

    Serkan Erboral said:
    2. Is it possible to add an external input source of 26V as shown in diagram?

    In this case you will need an MCU to tell TPS25750 to turn off the Type-C port when you are using the external 26V input source.

    Serkan Erboral said:
    3. Usage of BQ25792 is not recommended for applications above 45W. Does this limit comes from the internal mosfets of buck boost converter? Sourcing a 45W system means the possibility of doubling the input current as it is the sum of the charging power and system power so a power requirement of 90W on the Buck boost converter. If the system works only with battery power (I mean no charging simultaneously) then using BQ25792 over 45W scenarios is also possible, right?

    Yes the 45W limit is due to the internal FETs. Trying to go above 45W will cause BQ25792 to thermal shutdown. If you have more question on BQ25792 please open a thread so the responsible team can provide you more detailed answer.

    Regards.

  • 0 in reply to Tommy Lin
    Prodigy 20 points

    1. your answer makes it %100 clear. What makes me confused is: the article compares two methodologies: below and above 45W scenarios. Since there is mcu only solution on one side I thought it is mandatory. My bad, possibly the writer only wants to show another possibility.

    2. I want to make clear about one issue, recommended operating voltage of VBUS and VSYS pin is 22V but absolute maximum is 28V for VBUS and not given for VSYS. Although the mosfets will be closed due to the reverse current protection, the VBUS voltage will go high till 26V because of the leakage currents of the mosfets. Would it be a problem applying 26V at the VSYS and VBUS?

    Regards,

  • +1 in reply to Serkan Erboral
    TI__Mastermind 31400 points

    Hi Serkan,

    From the PD controller side we only care about the VBUS voltage (to the Type-C port). We don't recommend applying any voltage higher than 22V on VBUS (from/to the Type-C port). Pushing to above recommended max can cause permanent damage to device.

    Maybe it is better to add a switch between the 26V input source and the back-to-back NFET to avoid leakage issue.

    Regards