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BQ40Z60: Current measurement

Michael Korolyov
Prodigy 180 points
Part Number: BQ40Z60

Hello everyone. I make a smart power supply using BQ40Z60. My configuration is 3s1p, 15 V adapter voltage, 1,7 A charging current.
I have configured chemistry and done all the calibrations. Everything works fine, and reported values are close to measured ones.
However, when I try to connect a charger, it works, and the measured curent is really 1,7 A, but the reported current value in BQ Studio is about 5 A!

Of course, it sets CHGC protection flag. I turned it off, but I don't feel right about it.
I am really confused why the consumprtion current is what it should be, but the reported current is so off. Can it be a layout issue?

I will really appreciate any help.

  • 0
    TI__Guru* 76230 points

    when you try discharging, does the gauge measure current correctly? If it doesn't, then it means your current calibration is not accurate. Pls follow  the instructions on the EVM user guide on how to calibrate current measurement.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Prodigy 180 points

    Hello, Onyx.

    Yes the discharge current is measured accurately. But when I connect the charger, things go bad.

    I have just noticed that PGND and GND on my board is connected under the chip, just as it is written in the datasheet:

    "Connect analog ground and power ground together using the thermal pad as the single ground
    connection point. Or use a 0-Ω resistor to tie analog ground to power ground (thermal pad should tie to
    analog ground in this case). A star connection under the thermal pad is highly recommended.",

    but on BQ40Z60EVM they are connected through current sense resistor only.