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USB-PD-CHG-EVM-01: USB-PD-CHG-EVM-01 - Modify for 2 Input / Reduce Current Leakage

Don Pitchford
Intellectual 255 points
Part Number: USB-PD-CHG-EVM-01
Other Parts Discussed in Thread: BQ25798, , TPS25750, TPS25751, TUSB8041, CSD87501L, TPS54531

Tool/software:

I am design PD system based off the USB-PD-CHG-EVM-01.     I have upgraded my TPS25750 to TPS25751 per another thread with Chris.   I have questions on the BQ25798 and wonder if I could get a bit of clarification:

Base System - 4 Cell Li-Ion batteries,  The USB-C will provide power (sink mode) as well as connected to TUSB8041 hub.   The system will also have a barrel connector to power & charge the batteries.   

1 -  The BQ will have 2 input, Barrel Plug (20V DC),  and USB-C to charge and power the system.    I am using the CSD87501L and wondering if I have them wired correctly.  (see attached schematic)

2 - I am seeing leakage on the USB-PD-CHG-EVM board with nothing connected but the battery pack.   What could we redesign to reduce the leakage.    I know TPS54531 & TLV7553 will draw power for the TPS25751.  Are they needed to be on?   Can I tied the EN to the SPST Power control?   I did look at "Ship FET mode" on the BQ, but it needs to be set via I2C.  I don't think it will be an option since power on would require a barrel connection.  I would like to reduce leakage as much as possible, but still be able to charge the batteries with the system is off via barrel or USB-C.   

output1.pdf

  • 0
    TI__Guru**** 163426 points

    Hi Don,

    Regarding 1, on the BQ25798 schematic, I have the following concerns:

    1. BAT/BATP/SYS pins are only rated for 20V.  To prevent damage at hotplug by a fully charged 4S pack, I strongly recommend adding a TVS diode on BAT pin.

    2. Ceramic capacitors derate with applied voltage.  A 25V rated 10uF capacitor with 16.8V on it will likely have effective capacitance of 2uF.  Please review your capacitors and confirm that that their effective capacitance after derating meet the minimum values below:

    Regarding 2, for BQ25798 ship mode, the I2C registers are available in battery only mode so the host could write the BQ25798 into ship mode.  If the TPS25751 does not require the TPS and TLV provided voltages, those could be disabled using their EN pins.  I have moved this post to the TPS25751 team for further clarification about the need for and timing of those voltages.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Guru 61281 points

    Hello,

        Yes, you can disable the PP5V and P3V3 and the TPS25751 will still operate in the dead battery mode (sink only) when the type-c is connected.

    Regards,

    Chris  

  • 0 in reply to Jeff F
    Intellectual 255 points

    Jeff,

    Thanks - I have added reverse protection diode as well as a TVS.    Just an oversight.

    Good point, I need to upgrade to 50V X7R caps.   They will give me 6-8uF at 16V.     

    Question, on Cpmid - With backup mode, need 70uF.   Can I use Polymer Can cap, such as Panasonic EEH-ZA1V470P with a few 10uF cermanics?  

  • 0 in reply to Don Pitchford
    TI__Guru**** 163426 points

    HI Don,

    Yes.  As long as the ESR is <<50mohm, you can use any capacitor chemistry.

    Regards,

    Jeff