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TSU6721 BC1.2 timing

Miles Cernauskas
Prodigy 230 points
Other Parts Discussed in Thread: TSU6721

Hello,

My customer is planning on using the TSU6721 and they have some concerns on the timing of the detection mechanism for BC1.2 that this switch includes, and how it will play with the detection in their existing platform. Please see questions below:

The datasheet is a little light on details, so I’m hoping you can help to answer a few questions I have:

  1. Looking for any description of the timing / sequence of events when the part is in “detection” mode.  I understand it waits for VBUS, then begins a detection routine including the ID pin and the D+/D- impedances.  Just need to understand how long this process takes after VBUS is valid.
  2. During detection mode, what electrical state is the switch in?  I’m assuming it’s fully open (meaning Hi-Z looking into the USB terminal from the SoC).
  3. After detection is done, how long does it take to switch over to the USB path in automatic mode?  Is this done in parallel with the VBUS load switch, or serially? 
    1. This is getting at the issue that our BC1.2 detection begins when VBUS is valid (at our PMIC, meaning out of the TUSB switch).  Ideally I would find out that by the time the VBUS switch gets fully thrown by the TUSB switch, the data lines are already switched over to the USB analog path.

  • 0
    TI__Mastermind 45380 points

    Miles,

    1.Looking for any description of the timing / sequence of events when the part is in “detection” mode.  I understand it waits for VBUS, then begins a detection routine including the ID pin and the D+/D- impedances.  Just need to understand how long this process takes after VBUS is valid.

    I found this thread when searching e2e that provides some more detail about the detection timings

    https://e2e.ti.com/support/interface/etc_interface/int-_etc_interface/f/397/p/335668/1171379#1171379


    The detection sequence from VBUS valid to completion includes a 8ms debounce time, ADC read about 80 ms, a charger detection sequence about 40ms.  Depending on the type of device inserted weather it is audio accessory or a charger accessory the detection time should be in the 100-200ms range. 

    2.During detection mode, what electrical state is the switch in?  I’m assuming it’s fully open (meaning Hi-Z looking into the USB terminal from the SoC).

    I found this thread when searching TSU6721 in e2e

    https://e2e.ti.com/support/interface/etc_interface/f/388/t/440526

    The switch will be in the default state which is all switches are "open" Hi-Z looking into the USB terminal from the SoC

    3.After detection is done, how long does it take to switch over to the USB path in automatic mode?  Is this done in parallel with the VBUS load switch, or serially? a.This is getting at the issue that our BC1.2 detection begins when VBUS is valid (at our PMIC, meaning out of the TUSB switch).  Ideally I would find out that by the time the VBUS switch gets fully thrown by the TUSB switch, the data lines are already switched over to the USB analog path.

    The load switch and USB path are switched in parallel and the timings are listed in the datasheet below. 

    The audio switch timings in the datasheet below

    The USB and URAT switch path timings are listed in the datasheet below. 

    Please let me know if you have further questions. 

    Thank you,

    Adam