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Original question:

To Apple IPAD charge, it can't get 2.1A charge current.

TPS2546: TPS2546: Charging current can't reach to designed value

cyan zhou
Expert 1500 points
Part Number: TPS2546

Hi Sir,

We are now testing TPS2546 for usb charging.

the laptop set TPS2546 as 1111 CDP mode, the RILIM_Hi is 20KΩ;

when plug usb device(VIVO cellphone) to start charging, the charging current is only 0.886A;  even when we adjust RILIM_Hi from 20K to 9.1K, the current is as the same as 0.886A.

Then set RILIM_Hi to 81.9K; output charging current is down to 0.477A.

check (Vin-Vout)/Iout=(4.98-4.9)/0.886=90mΩ, Close to the typical value(73mΩ);

according to Equation 1 in datasheet, the out put current value is abnormal.

Please help to check it, thanks very much.

TPS2546 BC1.2.pdf

  • 0
    TI__Mastermind 30000 points

    Hello Cyan,

    When the ILIM resistor is set to 20k ohm, it means that the maximum allowed current will be around 2.5A. However, that does not mean that the connected device will pull that much current. The maximum allowed charging for CDP is 1.5A as defined by the BC1.2 spec. However, this does not mean that the connected device will always pull 1.5A of current. The amount of current pulled from the portable device varies between devices as well as the battery percentage of the device. In your test setup, the TPS2546 is not limiting the current

  • 0 in reply to Adam Mc Gaffin
    Expert 1500 points

    Hi Adam,

    Thanks for your reply.

    Let me correct a message, all the test condition above is the same. cellphone model is oppo reno ace, Battery percentage is 70%-80%.

    In that way, When I set Rilim_hi to 81.9K, according to Equation 1, Hi current limit will be set as 50250/81.9=613mA;

    However, the actual test value is 0.477A;

    Do you know why that is?

    Waiting for you.

    Cyan.

  • 0 in reply to cyan zhou
    TI__Mastermind 30000 points

    Hello,

    There is a tolerance on the output current limit of the TPS2546. Assuming there is a tolerance variation on the resistor you are using, plus the tolerance variation of the TPS2546, having a  current limit of 477mA could be expected.

  • 0 in reply to Adam Mc Gaffin
    Expert 1500 points

    Hi Adam,

    As you said, the TPS2546 is not limiting the current when we set Rilim_hi as 20K (50250/20=2.5A),

    However, the charging current is still under 1A while TPS2546 is set by a CDP mode. Even when I charging multiple downstream devices, the charging current is never more than 1A.

    Do you know why？ and could you advise what to do about it?

  • 0 in reply to Adam Mc Gaffin
    Expert 1500 points

    Hi Adam,

    I share another test data with you: We use electronic loads to test the TPS2546 charging current, set electronic loads as constant voltage mode.

    As a result, the charging current  arrived arround 1.5A.

  • 0 in reply to cyan zhou
    TI__Mastermind 30000 points

    Hello,

    As stated earlier, it is up to the portable device connected to determine how much current it draws. If you have the current limit set to the 2.5A, and the device is advertising CDP charging scheme, then our device is doing everything to offer as much current as possible. If the portable device pulls less than 1A of current, then that is not related to our device but instead the charging characteristics of the portable device.

    Your electronic load test shows that our device is working as expected and is not limiting the current. 

  • 0 in reply to Adam Mc Gaffin
    Expert 1500 points

    Dear Adam,

    Thanks for your easy-to-understand explanation.