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TPS2549: Application of IC without Cable Compensation and No Data Communication

Kyle Muehlegg
Prodigy 60 points
Part Number: TPS2549
Other Parts Discussed in Thread: TPS2546, TPS2547

Hello,

I am looking to do a USB-A Dedicated Charging Port (DCP) and there are some parts from the datasheet that I am unclear on. For our application, we are looking to charge basic USB-A products with shorter cables (less than 3m).

1) Can you use this IC without cable compensation? If so, what do you do with the CS pin? Leave it floating? Connect to GND/VIN?

2) If I want to just do charging, I do not need DM_OUT/DP_OUT, correct? I can just leave them floating?

In the Typical Application section of the datasheet, it mentions that DM_OUT/DP_OUT go to "Host Controller," but I don't understand the purpose of it in this setup because it cannot send/receive data from a host controller in this case. If I want to exclusively do charging, floating the DM_OUT/DP_OUT pins is acceptable, correct?

  • 0
    TI__Mastermind 24196 points

    Hi Kyle,

    For systems that does not require cable compensation, I would recommend taking a look at TPS2546 (2.5A power switch with CDP/SDP auto switch) or the TPS2547 (same as TPS2549 but without cable compensation). Let me ask internally regarding how to set CS pin for unused cases. 

    Regarding DP_OUT/DM_OUT, those are meant to be connected to a host controller if you're planning on implementing USB data. TPS254x controllers first determine the BC1.2 charging scheme using the DP/DM pins and if data is applicable, it will pass through the controller from the IN to OUT pins. The EVM for TPS2546 demonstrates this cability: https://www.ti.com/tool/TPS2546EVM-064 

    If not needed (charging only), the OUT pins can be left floating. 

    Thanks and Regards,

    Raymond Lin

  • 0 in reply to Raymond Lin
    Prodigy 60 points

    Hello Raymond,

    Thank you for the reply! The TPS2546 works great for my application.

    My only question about it is the output capacitor (C_USB). It doesn't give a specific design guideline for its size. The TPS2546EVM link you sent has a 150uF tantalum capacitor, but I'm unsure if that big is necessary. What are the recommendations for it?

  • 0 in reply to Kyle Muehlegg
    TI__Genius 13835 points

    Hi Kyle,

    There is no specific design guidelines for its size. This capacitor is used for output discharging when changing states as seen below:

    The only criteria that must be met is falling withing the discharge times when changing states. 

    Our recommendation on this device would be to follow the EVM schematic as this is a tested and proven working design.

    Very Respectfully,

    Brandon Beader

  • 0 in reply to Brandon Beader
    Prodigy 60 points

    Hello Brandon,

    I apologize for such a late response, but I had one small follow-up question with the new recommended chip.

    If I just want to use DCP_Auto, what is the difference between:
    CTL1 = 0, CTL2 = CTL3 = VIN

    CTL1 = CTL2 = 0, CTL3 = VIN

    The only difference is the note that says "DCP Load present governed by the Load Detection - (Non Power or Power) Wake limits".

    If I am just using a DCP application, can I use either setup? 

  • 0 in reply to Kyle Muehlegg
    TI__Genius 13835 points

    Hi Kyle,

    The difference is in the status output. DCP load present sets a current threshold that must be met in order for this to output low (logic 1). This threshold is set based on your ILIM_LO setting and according to table 2:

    For more details, I answered this in a seperate thread: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1194427/tps2546-datasheet-question-table-3---mode-selection

    Very Respectfully,

    Brandon Beader