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TPS25810: Simplest Docking Station/Charging Dongle using BC1.2

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Part Number: TPS25810

I need to build a "power source" which sits between an existing Type-C tablet and an existing USB 2 device tree.

Tablet with Type-C port -> "power source" -> existing USB 2 device tree (mice, storage, and other goodies).

"power source" connects to a wall wart. It constantly charges the Tablet with 5V, and supplies 5V to the USB peripherals.

So "power source" is like a docking station with USB 2 Host Port downstream but no extra features (no Displayport output, no connection to Superspeed signals).

Since the Tablet is controlling the USB peripherals, the Tablet thinks this is a "Type-C->USB 2.0 OTG" situation.

USB 2.0 OTG is not covered in the Type-C spec. Since Type-C has no ID pin, I don't know how to tell the Tablet to be the host.

(PD has DR_SWAP, but I don't think that is needed for super simple situations where CC wires may be unconnected.)

1) How does Type-C OTG work when only the USB 2 signals are used?

I bought the TPS25810 eval kit. It is a DFP and charges the Tablet, but has no pass-through USB connection.

The TPS25810 advertises that it can deliver 3A, but the target tablet needs to use BC1.2 (the TPS2513/2514) to get more than 500 mA.

A note here suggests that a TPS25810 plus a TPS2546 chip might be a solution.

The TPS25810 is a DRP for power, and the TPS2546 indicates that it is a CDP enabling the USB 2 tablet to get more power.

My read of the TPS2546 spec indicates that it expects peripherals to be on the BC1.2 side, with a pullup on D+ or D-.

Our system will never see peripherals on the BC1.2 side, That will be the Tablet as Host. Peripherals will be on the DM/DP_out side.

2) Will TPS2546 function with a Host on the DM/DP_IN port and a USB peripheral on the DM/DP_OUT side?

The solution in this forum read "The TPS2546 will need to share the same 5V supply as the TPS25810."

3) I connect the 5V power inputs together. But do I connect the switched USB 5V outputs together, towards the connector?

To recap:

Tablet with Type-C port -> "power source" -> existing USB 2 device tree (mice, storage, and other goodies).

USB 2.0 data goes in the order shown. No Superspeed signals at this time...

Power, however, starts in the middle and goes to both Tablet and USB devices. Want this to work for both USB 2.0-only and full USB 3 PD tablets.

4) What TI devices can I use to achieve this? Prefer no microprocessor intervention.

5) What eval boards can I flying-lead together to prove it?

Thanks

  • Hello Lawrence,

    1. Here is the USB org document that covers OTG

    USB_OTG_and_EH_3-0_release_1_1_10May2012.pdf

    2. If you set the TPS2546 in CDP mode, it will always pass through data signals to any portable device connected to it. Also, the TPS25810 is not a DRP in regards to power. It can only act as a source (will only pull up the CC lines never pull down)

    3. Depends on what you are trying to accomplish with your system. If the TPS2546 will always stay in a single charging mode (i.e CDP) then you do not need to connect them together. But if you're having the TPS2546 changing charging schemes, and the TPS25810 is connected to VBUS, then you will need to connect the OUT from the TPS2546 to the TPS25810 in a way that would disable VBUS during a change in charging schemes. I've attached the BC1.2 spec that talks about the need to discharge VBUS for a mode change. The section is 4.6.3

    4442.BC1.2_FINAL.pdf

    4. The TPS25810 and TPS2546 solution would work acting as the source, but it could never act as the portable device. Would need another series of devices to act as the portable device and start that negotiation

    Regards,

    Adam McGaffin

  • In reply to Adam Mc Gaffin:

    The two documents you pointed to do not cover the case where a Type-C connector is involved.

    The BC1.2 document Figure 3-1 part 3 shows PD (Portable Device) -> ACA (Accessory Charger Adaptor) -> Accessory. (like USB device)
    The fourth section shows an ACA-Dock. Very similar.
    These allows the ACA to charge the PD while allowing the PD to control the USB device(s). This is what I want to do.

    The Portable Device in figure 3-1 uses a u-AB receptacle with ID pin, not a Type-C connector.
    Type-C does not have an ID pin.
    Simple Type-C endpoints might only connect USB 2.0 signals and VBUS. There is no concept of ID pin.
    I don't see how this will work with a PD with a Type-C connector.

    In the case where the PD or the ACA doesn't support PD/CC, I don't know how to supply power from the ACA to the PD, while having the PD serve as USB 2.0 Host to operate downstream USB devices.
    I think the ACA will start out as A-Host to supply power.
    The OTG doc does not show how an A-Host can cause a Role Swap.
    In any case, I don't want the ACA to ever serve as a Host for Data Purposes.

    In the case where both the PD and the ACA support PD/CC, I think I know how the ACA can supply power to the PD.
    ACA starts as DFP, and (optionally) supports BC1.2 to allow higher current charging to an older PD.
    Then I think the ACA needs to do a DR_SWAP.
    I don't believe the TPS25810 knows how to issue a DR_SWAP.

    I bought an eval board for the TPS25810 and one for the TPS2546 to test things out (not arrived yet).
    But I don't think it is going to work.

    To repeat:
    USB Power direction:
    Portable Device with Type-C connector <-- ACA --> USB Peripheral

    USB data signaling direction:
    Portable Device with Type-C connector --> ACA --> USB Peripheral

    ACA can have a PD controller, and can have a BC1.2 host-side interface.
    ACA is not itself a USB device.

    I am sorry, but I still don't see how to do this.
    Especially using a TPS25810 + TPS2546 in the ACA to send power to the PD.
    I don't see how to issue DR_SWAP, if it is needed.

    Please contact me with TI component numbers.
    I would like to buy starter kits and prototype the solution.

  • In reply to Lawrence Butcher:

    Hello Lawrence,

    If you are wanting a ACA dock, then no I do not believe you can use the TPS2547 + TPS25810. Doing a little bit of searching, I did find this one thread that could be of potential help. However, they don't list what the device is that is able to source power to an upstream device. Would recommend posting a question in that forum and reference the attached E2E post.

    Regards,

    Adam McGaffin

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