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TPS2547: Vbus Discharge when charging in system S3 and S5 mode

Max Guan
Intellectual 1350 points
Part Number: TPS2547

Hi team,

Customer reported that they see Vbus discharge in the charging process in system S3 and S5 mode.

Noted that, in S3 and S5, TPS2547 under DCP/Auto mode. (And CDP in S0).

Please check the attached schematics and waveforms and help to confirm if this discharging is normal behavior?

The tested cell phone is with 50% capacity Xiaomi6 with Type-A to Type-C cable. Also need your help to explain what mode is in S3 and S5. It seems not DCP for me. And do you have related documents could share to me to help my learning?

Thanks for your help.

Max 

S0:

S3&S5:

DT-MIC2 USB3.0 Charger--20181208B.pdf

  • 0
    TI__Intellectual 1350 points

    Hi Team,

    Any updates on this please?

    Thanks

    Max

  • 0 in reply to Max Guan
    TI__Mastermind 27495 points

    Hello Max,

    For detection renegotiation, the BC1.2 spec states that a downstream port is allowed to act as an SDP, CDP, or DCP, and to change between these roles. However, in order to force an attached portable device to repeat the charging detection procedure, a downstream port is required to:

    - Stop driving VBUS

    - Allow for VBUS to drop less than 0.7V

    - Wait for a time of 100ms

    - Start driving VBUS

    So seeing VBUS discharge is expected behavior. Hope this answers your question. If so, please click THIS RESOLVED MY ISSUE

  • 0 in reply to Adam Mc Gaffin
    TI__Intellectual 1350 points

    Hi Adam,

    Thanks for your update.

    I understand there are chances when Vbus need to discharge for mode transition or load detect.

    Some questions need your help to clarify:

    1. Checking the S0 waveform we can find that CDP is negotiated and from CTL pin and schematics we can see load detection is enabled. So why in this case Vbus not discharged for load detection feature?

    2. Checking S3/S5 waveforms, Originally Ibus already loaded, but seems D+D- start communicating and then Vbus discharges to negotiation another mode? Is this right? So here also from schematics and CTL pin voltage, we can see that it is configured as DCP/Auto mode. From D+/D- I suppose this is not DCP right? So could you help to clarify what's the mode negotiated before and after discharge in S3/S5 waveform please?

    Thanks very much for your help.

    Max

  • 0 in reply to Adam Mc Gaffin
    TI__Intellectual 1350 points

    Hi Adam,

    Add another two questions.

    3. When transfer from S0-S3 (config. from CDP to DCP/Auto), seems Vbus runs two discharges with different D+/D- behavior. Could you explain to me why 2 discharges are required and what mode are negotiated respectively in these two discharges.

    System change from S0 to S3:

    4. Seems all other discharges are about 2s but when translated from S3-S0, the discharge lasted for around 300ms. Is this normal? And any spec to define the discharge time?

    System from S3 to S0:

    Thanks for your help

    Max

  • 0 in reply to Max Guan
    TI__Mastermind 27495 points
    Hello Max

    1. VBUS does not need to discharge during load detection while remaining in CDP mode.

    2. Yes, while the TPS2547 is in DCP_Auto mode, it will also try to determine if a not compliant device is connected and provide the correct charging scheme (ex. Divider 1). You can read more about this feature within section 8.4.1 of the datasheet.

    3. Yes, this is expected behavior as well. The first discharge is transitioning is due to the transition from CDP to DCP, and the second one is because of DCP_auto mode
  • 0 in reply to Adam Mc Gaffin
    TI__Intellectual 1350 points

    Hi Adam,

    Thanks for your explanation for me.

    Basically understand the behaviors now~ Will go through the datasheet detailedly and let you know if I have further questions.

    Max