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TPS2541A: Using a USB Port Power Switch and Have few queries before going for Fab

chethan md
Intellectual 840 points
Part Number: TPS2541A
Other Parts Discussed in Thread: TPS2541

Hi, 

I am Chethan from Celliber technologies Bangalore. 

I am designing a product where in I am using a 4-Channel USB Hub and I am exposing 2 Type-A Standard USB2.0 ports to the external world (other 2 ports of hub are being used internally).

I want to support 1.5A charging current via any one of these port (BC1.2), so i am using TPS2541ARTET port power switch, and I have few questions for which i need answers/suggestions before i move on.

I don't have any resources to control the switch, such as no GPIOs from any controller, so I am planing to use the Port switch in stand alone mode by hard wiring the CTL pins and ILIM pins.

Available power budget on +5V rail in my system is 2.5A, so i am planning to support CDP on one port and SDP on another port. 

  1. For Port1 [U16 switch's path in schematics]: I am planning to support CDP by hard wiring CTL1, CTL2,CTL3=111 and choosing the ILIM0=30K (ILIM_SEL=0,and set point =1600mA). In this scenario, the switch is hardwired to support CDP but if the CDP handshake fails from peripheral device (when non BC1.2 compliant peripherals plugged in) what will happen? does the peripheral negotiates to SDP and if SDP negotiation works does the peripheral device just draw SDP's 500mA current even though the switch is hardwired fro CDP? [See the attached shematics for the implementation]
  2. For Port2 [U14 switch's path in Schematics]: I have hard wired the CTL1,CTL2,CTL3=110 and ILIM0=60K (ILIM_SEl=0 and trip point=800mA, In this case I assume even if we connect BC1.2 compliant peripherals, the negotiation fails for CDP and falls back to SDP. is my understanding correct?
  3. If above approach is fine, then Since I am not at all using ILIM1, can it be left unconnected?
  4. if i wish not to comply to BC1.2 spec and hard wire both the ports to CDP config i.e. CTL1,CTL2,CTL3=111, and limit the current to may be ~1.2A/port, then the CDP negotiations work well for BC1.2 compliant peripherals but my both ports will be able to charge at ~1.2A, I am not sure if this is going to work, please let me know if this approach has any issues?

Attaching my schematics for reference.

  • 0
    TI__Mastermind 28830 points

    Hi Chetan,

    1. The BC1.2 handshake starts with the portable device sending detection signals. Based on the feedback it receives from the BC1.2 source device, the portable device will begin to sink the specified current. For CDP mode, you are correct it is up 1.5A and SDP mode can only supply up to 500mA. So if the TPS2541A device is in CDP mode, but the device portable device for some reason does not detect CDP, then yes, the portable device will only pull up to 500mA of current. The TPS2541A will still be able to supply the 1.5A of current, but the phone decides how much current to pull from the source charger.

    2.  The device negotiation will not fail CDP mode, but instead the TPS2541A will advertise for SDP mode. The difference between SDP mode and CDP mode is that CDP has a maximum charging current of 1.5A while SDP mode only supplies 500mA of current.

    3. I would keep ILIM connected as a fail safe, in case the portable device pulls more current than what is allowed for that charging mode

    4. This will work, but I'm not sure why you would want to do this . You do not gain anything, but only limit the current that you can charge your devices at and are then no lo9nger BC1.2 compliant.

    Let me know if this helped answer your questions! If so, please click This resolved my issue

  • 0 in reply to Adam Mc Gaffin
    Intellectual 840 points

    Hi, 

    Thanks for your support. You have answered all my questions which really helped me to move on with my design.

    Before closing this ticket, i would like to take your feedback on the last item which wasn't very clear to me.

    1. Can we configure to CDP and set the current limit to ~1.2A? in this case the peripheral device tries to pull 1.5A as CDP negotiation succeeds, but switch will limit current to 1.2A as per ILIM settings, does the switch gives FAULT interrupt in this scenario?

    The whole idea is to configure both ports to CDP and set ILIM to 1.2A, so that I can charge BC1.2 compliant devices at 1.2A (>500mA) from both the ports. However I know my host will not be BC1.2 compliant. Can i take this approach.

  • 0 in reply to chethan md
    TI__Mastermind 28830 points
    Hi Chethan,

    Yes, if you would like, you can configure the device that way to where CDP mode only outputs 1.2A. It will send a fault, but will not turn off the device. I personally would not recommend this configuration, but the part can allow it.

    Let me know if you have any other questions or if this answered them!
  • 0 in reply to Adam Mc Gaffin
    Intellectual 840 points

    Hi Adam,

    Understood. I will go with 1 CDP and 1 SDP port. Thanks for the support. I am closing the ticket.

  • 0 in reply to chethan md
    Intellectual 840 points
    Forgot to ask one thing,

    Do you see any issues with interoperability between Microchip's USB Hub USB2514BI/M2 and TI's TPS2541A ??
  • 0 in reply to chethan md
    Intellectual 840 points
    Because USB2514BI/M2 also has inbuilt BC1.1 detection circuit. Since anyways I have to use a USB switch on my board, i would rather use TI's BC1.2 capable TPS2541. I am bit scared if i end up in any interoperability issues between Hub and Switch.