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BQ25792EVM: IBAT_ADC Monitoring Charge and Discharge Current

Lee Nash
Prodigy 30 points
Part Number: BQ25792EVM
Other Parts Discussed in Thread: BQ25792, USB2ANY, BQSTUDIO, BQ25790

Hi,

I've purchased the BQ25792EVM evaluation board to evaluate the suitability of the BQ25792 Battery Charger IC for creating a UPS for an embedded platform.

One of the features that drew me to this device was the provision of an I2C interface that allows for a wide range of information to be extracted and in particular the ability of the device to report current flow from both the charger and battery.  For evaluation I've been using the Ti Charger GUI along with USB2ANY adapter to read the register status.

The issue I'm having is that the datasheet implies the REG33_IBAT_ADC register will report the current flow both into the battery as well as out of it but I'm not seeing any current flow reported when current is being taken from the battery.  The block diagram on page 26 of the datasheet (excerpt below) shows ICHG circling a connection that goes to SYS which to me implies the current path into and out of the battery is monitored.

When the battery is being charged the register shows a positive current value but when the power supply is removed and the battery is being discharged through the SYSTEM connection, the current flow reads as zero?  Is this correct or have I misinterpreted the datasheet or perhaps am I missing some information?

Any help and advice will be appreciated.

Thank you.

  • 0
    TI__Guru**** 166176 points

    Hi Lee,

    There was an issue with the early version of the BQSTUDIO GUI.  Attached is possibly a later version which is hopefully fixed.  The later version may only be on my bench computer.  I am frozen in at home in Dallas TX with my laptop or I would test quickly on my lab bench for you.    Even if it is not fixed, you can still read the 16 bits in the ADC register on BQSTUDIO register view and convert from 2's complement to get the discharge current.

    Also, if have TI's USB2ANY box, you can access using using online GUI Composer website.

    Regards,

    Jeffhttps://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/5050.Charger_5F00_2_5F00_00_2D00_bq25790_5F00_92.bqz

  • 0 in reply to Jeff F
    TI__Guru**** 166176 points

    One more thing.  In OTG mode (and possibly HiZ) you have to enable the IBAT bit/pin (REG14bit5) in order for the ADC to measure battery discharge current.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 30 points

    Hi Jeff,

    Thanks for your reply.

    Unfortunately I can't use BQSTUDIO as I don't have an EV2300/2400 USB-Based PC Interface Board, so I'm stuck with the online GUI for now.

    I've attached a few screenshots from the Ti Charger GUI, the first showing the Register Map when I've disconnected the input PSU and I'm running an external load from the battery alone, pulling around 1A, yet the value read back is 0xFFF6 (DEC -10, or 10mA!).  The second screenshot is with the battery being charged which correctly shows the charging currents.

    Seems like the GUI is able to display negative values but I've not seen anything below -10mA?

    Are you able to confirm if the BQ25792 IC is meant to be able to measure discharge current from the battery to the SYSTEM connection?

    Thanks again.

  • 0 in reply to Jeff F
    Prodigy 30 points

    Hi Jeff,

    I didn't see your second reply until after I'd posted my own.

    You were completely correct, I had to enable the "EN IBAT Pin" bit in REG14 and now it's reporting the current correctly, brilliant.

    Thank you so much for your response, it's been really useful!