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Original question:

TPS2549: Data Line Signal Switches condition

TPS2549: CDP Detection circuit condition

Koshi Ninomiya
Expert 5455 points
Part Number: TPS2549

Hi Team,

When TPS2549 is set in CDP mode, after CDP handshaking (after CDP detection circuit outputs ~0.6V on D- line), what condition will connection between the CDP detection circuit and D- data line?
 - The CDP detection circuit output is still connected with the D- data line, but output of the CDP detection circuit becomes Hi-Z?
 - There is a switch between the CDP detection circuit output and the D- data line, and the switch becomes off after the CDP handshaking?

Thank you.

Best Regards,

Koshi Ninomiya

  • 0
    TI__Mastermind 30000 points

    Hello Koshi,

    The CDP enumeration process is described in section 8.4.4. In order to determine CDP charging capabilities, it takes a two step process of putting voltage on both the D+ and D- line. From the datasheet:

    The second step is necessary for portable equipment to determine whether the equipment is connected to a CDP or a DCP. The portable device outputs a nominal 0.6-V output on the D– line and reads the voltage input on the D+ line.

    Hope this answers your question. If so, please click THIS RESOLVED MY ISSUE

  • 0 in reply to Adam Mc Gaffin
    TI__Expert 5455 points
    Hi McGaffin-san,

    I understand the CDP enumeration process. After completed the two step process, I want to understand the connection condition between the CDP detection circuit output and the D+/D- data lines.
    a) The CDP detection circuit outputs are still connected with the D+/D- data lines, but outputs of the CDP detection circuit becomes Hi-Z?
    b) There is a switch between the CDP detection circuit output and the D+/D- data line, and the switch becomes off after the CDP handshaking?
    Which one?
    Thank you.

    Best Regards,

    Koshi Ninomiya
  • 0 in reply to Koshi Ninomiya
    TI__Mastermind 30000 points
    Hello Koshi-san,

    B. The TPS2549 has internal switches that open and close, applying the voltage levels needed on D+/D- in order to advertise CDP charging.
  • 0 in reply to Adam Mc Gaffin
    TI__Expert 5455 points
    Hi McGaffin-san,

    Please let me understand one more thing.
    What conditions does the internal switches of CDP detection circuit become open and close?
    1) Before plug in connector (CDP-SDP auto switch mode setting & EN=High):
    What condition is the internal switches of CDP detection circuit, open or close?
    1) Plug in connector:
    How does TPS2549 detect plug-in and close the internal switches of CDP detection circuit to start CDP handshaking?
    2) Plug out connector:
    After the CDP handshaking, the internal switches of CDP detection circuit became already Off.
    How does TPS2549 detect plug-out?
    And what operation does TPS2549 do at plug-out? (Close the internal switches of CDP detection circuit for next plug-in?)
    3) Re-Plug in connector:
    How does TPS2549 detect re-plug-in and close the internal switches of CDP detection circuit to start CDP handshaking?
    Thank you.

    Best Regards,

    Koshi Ninomiya
  • 0 in reply to Koshi Ninomiya
    TI__Mastermind 30000 points

    Hello Koshi-san,

    1. The internal switch is open. It is waiting for the initial enumeration signal to be sent from the portable device over the D+ line. The TPS2549 will detect this voltage and send the response signal on the D- line by closing the internal switch, applying a voltage on D-.

    1. The CDP handshaking is initiated by the portable device, and the charger (TPS2549) responds accordingly depending on the charging mode it is set to. Below is a picture of the CDP handshaking, showing the sent signals from both the charger and portable device

    2. Yes, the internal switches to open so that a voltage is not continuously help on the D+ or D- lines

    3. The TPS2549 will determine if a device has been removed or entered into a low power state based on the current draw over VBUS. If a device is reinserted, the enumeration process will start over and the portable device will send a signal over the D+ line.

    Hope this helps answer your questions