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bq24266 USB interaction

Stefano Infante
Expert 2320 points
Other Parts Discussed in Thread: BQ24266, BQ24392

Hi,

I am evaluating a battery charger with power path management for a new portable device I am working on.

bq24266 seems to be a good choice, but it is not clear to me how it interacts with USB.

If I set IUSB3:2:1 to 001 (input current limit 500 mA) and the host only assures 100 mA, what happens? Does bq24266 use the available current or does it require microcontroller to set IUSB the "right" way?

And, as I cannot know whether the USB cable is attached to a host PC ora a wall adapter, how should I configure IUSB in order to allow bq24266 to use all the needed and available input power?

Thanks in advance.

Regards,

Stefano

  • 0
    TI__Guru**** 166096 points

    The bq24266's IUSBx pins are expecting to be set by a microcontroller after USB enumeration.  For start up, before USB enumeration, you could a USB communication chip like bq24392.  If you do not use such a chip, you set the IUSB pins to a default setting (like 100mA or 500mA) and let the VINDPM feature prevent the input voltage from collapsing by scaling back the input current limit.

     

     

  • 0 in reply to Jeff F
    Expert 2320 points

    Hi Jeff,

    to be honest, I did not take USB enumeration into account (my fault).

    My system should have a power path management, since I need the system to be powered from "wall" or from battery, and I would like to use a single connector for power and data (USB data will only be used when in configuration mode).

    In my system I would use bq24266 in order to manage power and another IC as an USB to UART converter.

    If I correctly understand bq24392 functionality, it is able to deal with USB host (enumeration) and tell MCU if it can or cannot draw more current; besides that, it is transparent to USB data (it has both D+ and D- as inputs and outputs). So, in order to get what I want, I could use it in combination with the two ICs I mentioned before (bq24266 and UART to USB converter).

    Is it ok? Is there anything else I should take into account?

    Thanks for your help.

    Stefano

  • 0 in reply to Stefano Infante
    TI__Guru**** 166096 points

    There are essentially three steps to the USB Battery Charging spec:

    1.  Primary detection

    2.  Seconday detection

    3.  Enumeration

    the bq24392 only helps with 1 and 2 and is transparent to USB data because it only communicates during the first few ms after power up, which USB has blocked out for this purpose.

  • 0 in reply to Jeff F
    Expert 2320 points

    Ok, then I could use bq24392 for steps 1 and 2; but what should I do for taking enumeration into account?

    Please help me to evaluate if these steps are ok:

    1. MCU sets GOOD_BAT to bq24392

    2. After the detection phase, bq24392 tells MCU what kind of device was attached (table 1 in bq24392 data sheet, page 8)

    3. If it is a standard port, data can be exchanged (the USB/UART converter can be used); bq24266 can be set initially to draw 500 mA, and then, if VIN_DPM goes too low, it can be set to draw only 100 mA

    4. If bq24392 tells the MCU it has detected a charger, then enumeration will not occur and bq24266 can draw current as indicated by bq24392

    So, I have a complete USB charging and communication "facility" with just a couple of ICs. Is it correct?

    Thanks again

    Stefano

  • 0 in reply to Stefano Infante
    TI__Guru**** 166096 points

    The bq24392 is only used to establish whether or not to charge and if so, how much to charge BEFORE enumeration  It will only tell you whether the USB port is standard charging port (SDP) (or non-compliant port) and therefore should only allow 100mA charge until enumeration or is downstream charging port (DCP) and can charge at full current.   After enumeration, you are allowed to change the USB charging current.

    The VIN_DPM circuit is an analog circuit that scales back the input limit if the voltage at the charger's input pin starts to droop.  It is a failsafe that technically does not meet the USB spec but will prevent the USB port from collapsing if too much current is attempted to pulled from it.

  • 0 in reply to Jeff F
    Expert 2320 points

    Ok, then I need an enumeration device, especially in order to get the full 500 mA when connected to host PC.

    The USB-to-UART device (FTDI FT234XD) does enumerate, but I don't know if it allows to draw 500 mA or simply limits, after the enumeration phase, the system to draw the basic 100 mA.

    Hence, if enumeration does not allow to draw 500 mA, I will not be able to get all that current, in any case, and I will have to limit to 100 mA when attached to a host, while I can draw 1 A or so when attached to a wall charger.