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TPS2540 EVM not able to charge Android or iPhone?

MikeH
Guru 15580 points
Other Parts Discussed in Thread: TPS2540

I have the TPS2540 EVM with CTL1,2,3 set to 0,x,1 to enable auto-detect DCP mode. However, neither my HTC Android, nor my iPhone will draw more than ~180mA. Shouldn't they draw substantially more current since both batteries are somewhat low (~20% charged).

  • 0
    Guru 15580 points

    ....correction. The iPhone will charge but only at ~520mA. I would expect it to be much higher current draw. The Android is ~180mA which should be much higher also. Any ideas? I can see the D+ and D- pins toggling during the detection phase but the Android will not charge at a higher rate.

    Suggestions welcome!

    Thx,

    MikeH

  • 0 in reply to MikeH
    TI__Mastermind 42795 points

    You are not doing anything wrong. The portable device must  “ask for permission” to charge at a higher current. If the portable device doesn't follow the new industry standards, they can charge at a lower current in some cases. We have had similar reports about problems with the Android so most lilely the Android is not compliant with the USB Battery charging standard.

  • 0 in reply to Eric Wright
    Guru 15580 points

    Eric Wright said:
    We have had similar reports about problems with the Android so most lilely the Android is not compliant with the USB Battery charging standard.

    Interesting. I would have thought it would follow one of the recent standards (BC1.1 or BC1.2) since the HTC eVO 4G is fairly new.

    FYI, I used the output of my HTC wall adapter as the input to the EVM USB port, plugged the HTC into the bottom USB output connector (power only) and the charging current is still around 250mA. I guess the phone does not draw more than 250mA for charging. Strange.

  • 0 in reply to MikeH
    Guru 15580 points

    Eric,

    In terms of Apple charging (iPhone), the chip is set for Divider Mode but I am only getting 1.8V on the D+ line and 2.2V on the D- line. These should be 2.0V and 2.7V for the iPhone to properly detect a DCP and charge at its max rate. Why are the voltages so low? The incoming VBUS is 5.0V.

    MikeH

     

  • 0 in reply to MikeH
    TI__Mastermind 42795 points

    DM_IN open circuit should be 2.7V and DP_IN should be 2Vin nominally divider mode. The internal source impedance is 10k-ohm so any external impedance will divide the in circuit voltage readings. If you are using a meter or scope to measure the open circuit voltage on the EVM at TP8 (DM_IN) and TP7 (DP_IN), the series resistors (R8, R7 respectively) + meter/scope between the D lines and the test points will cause somewhat of a divider effect depending on the meter/scope impedance.

    So, I guess the big question is how does the iPhone load the data lines?

  • 0 in reply to Eric Wright
    Guru 15580 points

    Eric,

    Eric Wright said:
    If you are using a meter or scope to measure the open circuit voltage on the EVM at TP8 (DM_IN) and TP7 (DP_IN), the series resistors (R8, R7 respectively) + meter/scope between the D lines and the test points will cause somewhat of a divider effect depending on the meter/scope impedance.

    Bingo. The values of R8 & R7 are 1M ohm. That's a bit high for most DVMs and will cause inaccurate readings. I suggest you guys lower these to ~100k or so.

    thx,

    MikeH

     

  • 0 in reply to MikeH
    TI__Mastermind 42795 points

    Thanks for the suggestion.

    We chose the R7/R8 values to be large so that impact to high speed signal integrity would be minimal. That being said, I suppose 100k would be a good compromise. I plan to update the EVM user guide soon and will at least make a note about the impact of DMM readings at TP7/8 with the 1Meg resistors.