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Using TPS2540/41 in a DCP Application

Marc Nussbaum
Prodigy 50 points
Other Parts Discussed in Thread: TPS2541, TPS2540, TPD2E001

Don't know why my cut and paste did not work the first time I posted...

I plan to use either the TPS2540 or TPS2541 in a charger application that will implement a DCP. I need to work with both Apple protocols (iPhones) and BC1.2 compliant devices.

1: My supply is a Lithium ion battery and I would like to limit current when supplying the iPhone to 500mA. While I realize this can be done with setting the constant current level of the chip, is there any way to internally or externally effectively convert the D+/D- output to levels of 2.0V on DP_IN and 2.0v on DM_IN instead of the standard divider mode negotiation of 2.7v and 2.0v (iPhone pulls about 1A)? The 2.0/2.0 tells the iPhone to only pull 500mA and this would avoid having to dissipate additional heat in the IC. If this is not possible, has anyone tried to limit an iPhone to 500mA using the TPS2540/1 device in DCP mode and does the chip overheat or continue to supply the current limited output. Also, in this situation, what sort of voltage drop should expect?

2: I understand the TPS2541 will discharge the output capacitor each time the chip is disabled and the TPS2540 requires 000 on the mode select lines to accomplish the discharge. Since I am building a DCP (Dedicated Charger Port) solution and I plan to use the AUTO detect between divider mode and BC2.1, is it best if I design so the discharge happens each time the chip is turned on/off? If I do not discharge the capacitor each time the chip powers up and the cap is still charged, will the AUTO select and discovery take place as necessary?

3: The data sheet talks about using both a common mode choke in the upstream data path and also a diode ESD protection array (TPD2E001) to protect the chip from ESD damage. Are doth really necessary to pass the CE tests (EM61000-4-2) if I am only building a DCP? The demo (EVM) board has both. Why isn't the TPD2E001 sufficient? Especially for a DCP application where there is no use for the data lines other than to handshake the power levels.

Thanks,

  • 0
    TI__Mastermind 42795 points

    Marc, sorry for the delay on this ... these are very good questions.

    1. We are not aware of a 2V/2V divider mode and as such haven't seen an application for this. In your application, can you utilize the ILIM selector to your advantage? As far as power dissipation is concerned when the power switch is fully enhanced the dissipation is negligable (for example at 1A, 75milli-ohms, the dissipation is 75mW). As current increases above ILIM, OUT will foldback. The IC is self protecting meaning that there is internal over temp protection as well.

    2.  The discharge cycle is to make sure the portable device attached is reset correctly (so that there will be correct handshaking for charger port identification). So, discharge is recommended. The TPS2540/41 does not rely on the discharge; the data lines will behave correctly during handshaking. Could you clarify what you mean by “turn on/off the chip”? Is it IN going down to 0V or disable the device (EN input)?

    3. We have found that in order to meet IEC61000-4-2 ESD, both are needed.