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Original question:

TPS2546: Mode Selection inquiry

TPS2546: TPS2546 CDP & DCP Auto application

Kelvin Tee
Genius 10035 points
Part Number: TPS2546

Hi 

The EE is designing TPS2546 and operates in two different modes ie during operation and during standby.

Could you help to edit / update table below to better understanding the device behavior on different modes.

Besides, changing CDP to DCP mode will result Vbus discharge which could harm the attached HDD on the USB port. As such, it is a good approach to shutdown TPS2546 and Vbus restart with delay (few seconds) when EE works on standby with DCP_Auto ? or do you have any other idea? (stays at CDP is not favorable)

Rgds
Kelvin

TPS2546 application table.xlsx

  • 0
    TI__Genius 9630 points

    Hello Kelvin,

    A misunderstanding that I see in your table is the operating mode column. The operating mode is dependent on CTL/ILIM pin input, not on the connected device. So if the pin input is 1111, the TPS2546 will be in CDP mode. It is then up to the connected device (thumb drive, etc) to pull the amount of current it needs. So even though the TPS2546 is in CDP, offering charging up to 1.5 A and data connection, not every device will pull the max current or utilize the data connection. However, the TPS2546 is still in CDP mode.

    CDP offers up to 1.5A and in order to be BC1.2 compliant, will not allow a device to pull more than 1.5A. This is shown in the TI BC1.2 Implementation document http://www.ti.com/lit/an/slvae17/slvae17.pdf pasted below:

    1070.TPS2546 application table.xlsx

    By shutting down the TPS2546, do you mean toggling the enable pin? Or are you referring to the VBUS discharge that occurs during mode change? 

    Thanks,

    Emma

  • 0 in reply to Emma Hoying
    TI__Genius 10035 points

    Hi Emma

    Thanks for fill up the excel. It is clearer after your input.

    About the CDP maximum current up to 1.5A,
    Refer to datasheet section 8.3.2, CDP "supplies a minimum of 1.5A", what does it mean?
    In the circumstance Vbus short to GND, what is the current limit?

    About the mode change workaround such as Operating to Standby

    1. Vbus (supplied by DCDC) will be turn off
    2. EE in standby
    3. After several seconds, the DCDC is enable (Vbus resume) and configure 0111(DCP_Auto)

    Rgds
    Kelvin

  • 0 in reply to Kelvin Tee
    TI__Genius 9630 points

    Hi Kelvin,

    The current the TPS2546 supplies depends on what the device pulls. That sentence of the datasheet may be confusing but the current limit on CDP is 1.5A and an attached device may pull less current depending on its current requirements. The TPS2546EVM could be a helpful learning tool in order to understand more thoroughly the device function. 

    If VBUS is turned off, any attached device that is transferring data that has not appropriately been ejected/spun down may be harmed. It does not matter if VBUS is dropping from the mode change or if it is dropping because the part loses power. 

    Thanks,

    Emma

  • 0 in reply to Emma Hoying
    TI__Genius 10035 points

    Hi Emma

    Thanks for the advise.

    We have tried several phones on the TPS2546EVM, here are some observations

    a. The Vin need to set 5.3V in order to get a 5Vbus to charge a phone. (about Ichrg 6-800mA)
    b. The Vin need to set 5.5V to get 4.7Vbus when the phone charge current is about ~1A or slightly above
    c. Two phones with Quick Charge feature (noted it is not applicable here), the normal charging current is only 500mA.
    d. When charging an Iphone, it take two to three attempts to charge the phone until the charging voltage/current stabilized.

    The voltage drop is a bit high. We worry it is worsen when charging current increases. Is this expected?

    When compare with the Phone List that you've shared, most of the phones could achieve charging current to 1 -1.5A. When we tested several phones, we could only achieve 500mA - 1A.

    Here is our test set up on the TPS2546EVM
    Connects external power supply to J1, J2 (no connection), JP3 set to 0110 (DCP_Auto)

    Could you tell us whether the test set up is correct?

    Rgds
    Kelvin

  • 0 in reply to Kelvin Tee
    TI__Genius 9630 points

    Hi Kelvin,

    Are you using an external power supply or a notebook as an input? A voltage drop is not expected. 

    Could you describe the charging voltage/current stability? When you say two or three attempts, are you talking about the negotiation process or are you cycling power on the TPS2546? The device will go through multiple DCP offerings in DCP_auto so this may be what you are seeing, and this is expected. A scope capture of the DP/DM lines would be helpful. 

    The TPS2546 has a ILIM_HI of 2.8 A so you are not running into a current limit issue. The portable device (phones in this case) are responsible for pulling the amount of current they need, so it could be the case that they are not pulling much current, despite the TPS2546 offering higher current. 

    This test setup is correct if you are trying to test DCP_auto.

    Thanks,

    Emma

  • 0 in reply to Emma Hoying
    TI__Genius 10035 points

    Hi Emma

    External supply to the EVM. There is some improvement after soldering the wire instead using clip the terminal. I will provide more data if it create a concern.

    About the datasheet section 9.1.2 stated CDP/SDP "Auto Switch" feature, what control pins does it referring to ? (CTL1/2/3/Ilim sel = ?).
    Does it mean it will automatically switch between CDP and SDP depending on phone connected (BC1.2 or non BC 1.2)?

    In the configuration 1111 (CDP)
    When looking at datasheet section 8.3.2 mentions host charge hand shaking logic to identify the port is CDP. 
    Does it mean only BC1.2 phone will be recognized as CDP, what about non BC1.2 phone?

    The question of asking, some phones were observed with poor charging current and reason is unknown.

    Rgds
    Kelvin

  • 0 in reply to Kelvin Tee
    TI__Genius 9630 points

    Hi Kelvin,

    The CTL pin is ILIM_SEL to change between CDP and SDP without a VBUS discharge, as shown below in the table.

    Please note that if the TPS2546 detects a non-compliant to the BC1.2 specification phone is attached, it will go through the below process, as described in section 9.1.2 CDP/SDP Auto Switch of the TPS2546 datasheet. 

    This auto-switching only happens if a device does not go through secondary detection. Any other time, to move from CDP to SDP2, the ILIM_SEL must be changed. When ILIM_SEL is toggled (1110 to 1111 or 1111 to 1110), there is no VBUS discharge. 

    Thanks,

    Emma

  • 0 in reply to Kelvin Tee
    TI__Genius 9630 points

    Hi Kelvin,

    The CTL pin is ILIM_SEL to change between CDP and SDP without a VBUS discharge, as shown below in the table.

    Please note that if the TPS2546 detects a non-compliant to the BC1.2 specification phone is attached, it will go through the below process, as described in section 9.1.2 CDP/SDP Auto Switch of the TPS2546 datasheet. 

    This auto-switching only happens if a device does not go through secondary detection. Any other time, to move from CDP to SDP2, the ILIM_SEL must be changed. When ILIM_SEL is toggled (1110 to 1111 or 1111 to 1110), there is no VBUS discharge. 

    Thanks,

    Emma

  • 0 in reply to Emma Hoying
    TI__Genius 10035 points

    Hi Emma

    The application doesn't require data connection. The main objective is to charge the phone only.
    In such case, does it still undergone CDP/SDP auto switch scheme for non BC1.2 compliant phone?

    Rgds
    Kelvin

  • 0 in reply to Kelvin Tee
    TI__Genius 9630 points

    Kelvin,

    It does not matter if the phone is utilizing the data connection, only if the phone is non-BC1.2 compliant. If the phone is non-BC1.2 compliant, it will go through the CDP/SDP autoswitch. 

    Thanks,

    Emma