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BQ24196: Understanding the OTG attributes of the BQ24196 device

Kim Turner
Prodigy 30 points
Part Number: BQ24196
Other Parts Discussed in Thread: TPS2514A, BQ24195

I am looking to use the BQ24196 battery charger IC.  I am getting a little confused.  I have a requirement for  a system that can

a) receive a dc adapter input to charge a LiFe cell

b) receive a USB VBUS i/p from to charge the above

c) power an external USB device via the VBUS pin.

I think the device mentioned above can perform this task. However, I am getting confused with how this is accomplished. I have no problem with understanding a) or b).  Option c) is confusing me.  The Data sheet seem to talk about VBUS as an input pin but seems to suggest in other application data that the battery via the boost facility can somehow supply power to the VBUS input line.  The other thing I do not understand is what is the purpose of the PMID pin and what does this term mean, Power Module I-Dent pin.  Does this connect to the USB ID pin?

  • 0
    TI__Mastermind 25800 points
    Hey Kim,

    Yes, the VBUS pin can be both an input pin when the user wants to charge the battery, as well as a ~5V and 1.3A capable power supply.

    This is our OTG mode that can only be activated when the there is no input source (wall adapter/USB input) at VBUS. Once turned on, through both the OTG pin (pulled high), and REG01[5:4] set to 10, you will have a regulated boosted output at VBUS.

    In regards to PMID, this is the actual input to the buck power stage as well as the output to the boosted stage. As such, in buch mode (charging), it is the high frequency current path that results from switching. Capacitance on PMID helps reduce EMI. In boost mode, the capacitance on this pin is used to mitigate output voltage ripple. This is not connected to the USB ID pin.

    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 30 points

    Hi Joel,

    Is there an application circuit that shows the BQ24196 acting as Host.  All the USB OTG explanatory data I have seen seems to suggest pulsing mechanisms on the D+/D- USB connector as well as a bunch of comparators to detect what is being pulsed/pulled down in order to be able to fully implement OTG Host capability.

  • 0 in reply to Kim Turner
    TI__Mastermind 25800 points

    Hey Kim,

    Unfortunately, this charger does not have D+/D- pins to establish the requirements of the OTG spec. 

    I did find one reference TI-Design we have that shows how we typically utilize the OTG function of the charger. Click here

    Apart from that, you may need some USB transceiver or switch along with your host MCU or uProcessor in order to fully establish the OTG protocol. 

    It seems that in this reference design, they have utilized the TPS2514A, a DCP controller to realize the OTG mode in some way to realize a DCP type of OTG device. 

    I suggest posting to the USB Forum group, as they may have more answers regarding the USB OTG Host setup. Our chargers essentially only provide the power-supply to that application. USB Forum

    Hope this helps,

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 30 points
    I was looking at the BQ24195. I noticed that it does not have a PSEL input but the schematic application has additional MOFET blocking when an external power adapter is required. I compared the BQ24196 & BQ24195 functional diagrams and I could not see any extra internal power steering/blocking mechanism that would negate the use of the extra MOFETs' utilised in the BQ24195 functional diagram. I assume that that they are still required on the BQ24196 variant if a external DC adapter is to be used. Can you confirm this for me.

    Regards, Kim
  • 0 in reply to Kim Turner
    TI__Mastermind 25800 points

    Hey Kim,

    The both the bq24196 and bq24195 would require the external circuitry if you are going to use either charger for a power bank/OTG application.

    Regards,
    Joel H