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Original question:

TPS25751: No output at PPHV

TPS25751: pp5V Problem

korcan tuna
Intellectual 300 points
Part Number: TPS25751
Other Parts Discussed in Thread: BQ25756, , , BQSTUDIO

Tool/software:

Dear Team,

I am currently working with the TP25751 and BQ25756 evaluation boards. I have implemented a setup based on both EVMs, aligned with your reference system design (video). The system operates as expected for both charging and discharging when using USB PD.

However, I am facing an issue related to 5V discharge without PD loads. Specifically:

  • When PP5V is supplied with 4.5 V, the discharge starts successfully.

  • When PP5V is supplied with 4.9 V or higher, the discharge does not start.

According to the datasheet specifications, the minimum voltage requirement for operation is 4.9 V. Nevertheless, the discharge does not initiate under these conditions.

Could you please advise on possible causes or provide suggestions to resolve this issue? I check reverse current and when pp5v is higher 4.9V there is no reverse current and pp3 is currently using.

Thank you for your support.

  • 0
    TI__Mastermind 30492 points

    Hi Korcan, 

    Thank you for reaching out!

    Could you share the .json file being used? 

    How are you varying the PP5V voltage on the EVM?

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Intellectual 300 points

    Hi Aya,

    PP5V is supplied additional with additional power supply. Json file is attached.

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  • 0 in reply to korcan tuna
    TI__Mastermind 30492 points

    Hi, 

    korcan tuna said:
    PP5V is supplied additional with additional power supply.

    Are you connecting the power supply to TP15 on the TPS25751EVM? Do you have any waveforms describing the behavior observed?

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Intellectual 300 points

    Hi Aya Khedr,

    Yes TP15 is used for this.

    Also one cell is used for project. Bq25756 is supported 1 cell according to datasheet specifications.

    Let me clerfy for you with the oscilloscope ss;

    CH1: VAC

    CH2: SW1

    CH3: DRV_SUP

    CH4: REGN

    1) When I selected PP1 source for PDO 1. Everthing is normal and working properly. 

    65W charger attached (20V/3A):

    5V source (Earpod box) source (5V/0.25A):

    Laptop USB port for source (20V/1.5A):

    2) I only make changes PP3:

    Here is the charging still working (20V/3A);

    When I connect to earpods or laptop, hiccup mode is seen

    During the hiccup mode, if I disconnect J8 ribbon cable, open the BQstudio, set EN_REV register output is goes into ON succesfully. At that moment no TPS25751 control.

    Another detail from the oscilloscope may show us for some reason TPS25751 may not the activated PP3 source. It can be seen from the below SS.

    During connected j8 cable TPS25751 tries sequently and VAC= 1.5V. No trying to switching can be seen from blue signal.

    When I disconnect J8 cable VAC = 2.1V

    Set the EN_REV from BQStudio VAC goes to the 0V then 2 times try and switching is become ON and charging to load with 5V/250mA from VAC.

    We need to find the actual reason. TPS25751 goes into somehow protection or dont allowed give time to start switching. Maybe it's just a timing issue I dont know. 

  • 0 in reply to korcan tuna
    TI__Mastermind 30492 points

    Hi Korcan, 

    Thank you for the additional information. I will review and provide feedback early next week. 

    Best Regards, 

    Aya Khedr

  • 0 in reply to Aya Khedr
    Intellectual 300 points

    Hi Aya,

    I have identified an issue: if PP5V is higher than 4.9 V or equal to 5 V, the IC begins discharging through the PP5V path, even though PP3 is selected. I verified this on the MOSFET(internal power path using pp5v). When this happens, the BQ25756 doesnt start switching, and tps25751 close vbus. This sequence repeats consecutively. 

    Is it possible? Could you control this?

  • 0 in reply to korcan tuna
    TI__Mastermind 30492 points

    Hi Korcan, 

    Yes, the TPS25751 begins sourcing through PP5V during the implicit contract for ~10mS and then switched over to PPHV (PP3). The BQ25756 will enable its power path when the switchover occurs. 

    Best Regards, 

    Aya Khedr

  • 0 in reply to Aya Khedr
    Intellectual 300 points

    Hi Aya,

    Yes, you are right. However, when PP3 is selected, VBUS is initially supplied from PP5V for around 10 ms as you mentioned. After that, TPS25751 shuts off VBUS and the output voltage repeatedly drops to 0 V in an on-off cycling manner. In this situation, switching does not transfer to PPHV (PP3). Why does switching occur when PP5V is lower than 4.8 V, but not when the voltage is at 5 V? Do I need to use a 5V/3A LDO in this design even though PP3 is selected?

    It seems PP3 is the source of the problem. As you can see in the oscilloscope captures, switching does not start. I have to use PP1 instead. Why can’t I use PP3?

    Thanks for your support.

  • 0 in reply to korcan tuna
    TI__Expert 8190 points

    Aya is out of office today but will be back tomorrow. 

  • 0 in reply to Ghouse Mohiuddin23
    Intellectual 300 points

    Hi,

    Is there any solution? Thanks for support.

  • 0 in reply to korcan tuna
    TI__Mastermind 30492 points

    Hi Korcan, 

    Thank you for your patience. I will provide feedback by Thursday. 

    Best Regards, 

    Aya Khedr

  • 0 in reply to Aya Khedr
    Intellectual 300 points

    Hi Aya,

    Is there any update?

  • +1 in reply to korcan tuna
    TI__Mastermind 30492 points

    Hi Korcan, 

    korcan tuna said:

    Another detail from the oscilloscope may show us for some reason TPS25751 may not the activated PP3 source. It can be seen from the below SS.

    During connected j8 cable TPS25751 tries sequently and VAC= 1.5V. No trying to switching can be seen from blue signal.

    When I disconnect J8 cable VAC = 2.1V

    Set the EN_REV from BQStudio VAC goes to the 0V then 2 times try and switching is become ON and charging to load with 5V/250mA from VAC.

    We need to find the actual reason. TPS25751 goes into somehow protection or dont allowed give time to start switching. Maybe it's just a timing issue I dont know.

    Have you tried to read the status registers using BQStudio? I can loop in a BQ expert to take a look as well. 

    I suggest also capturing I2C logs between BQ and PD EVMs when PP3 is selected to Source PDO1 (without BQ Studio connected). 

    Best Regards, 

    Aya Khedr