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Problem in reading Relative State of charge with BQ27200

Chiheon Kwon
Prodigy 90 points
Other Parts Discussed in Thread: BQ27200

HI.

I'm trying to make an battery monitoring system using BQ27200, and I have some problem.

I made a circuit as like BQ27200 typical application circuit in datasheet, and designed PCB.

Following pictures show circuit and PCB design what I made.

< fig 1. Circuit (nothing is connected with J2) >

< fig2. PCB Design >

After soldering all component in PCB, I read RSOC register using I2C Communication, but the value was always 0.

If I read flag register, it was always 0x28 or 0x08 which mean BQ27200 is in Calibration Process.

In addition, I measured Battery Voltage with BQ27200, but it always showed half of battery voltage.

What could cause those thing?

Actually  I didn't care Kelvin connection when I designed  PCB layout, could this incorrect Kelvin connection cause those problem?

Please help me out :(

-  Matthew -

  • 0
    Intellectual 765 points
    >Actually I didn't care Kelvin connection when I designed PCB layout, could this incorrect Kelvin connection cause those problem?
    This very bad - chip can't measure real current to R7..
    1. R7 - 0603? 20 mOhm?
    2. try read "0x09 - 0x08 VOLT Reported Voltage High - Low Byte" and compare with real voltage
    3. I can't see GND between (BAT-, R7,R9) and pins 3,11 bq27200
  • 0 in reply to jury noname
    Prodigy 90 points

    1. R7 is 0805 size, and 20 mOhm

    2. I tried it several time, but value was always half of actual battery voltage. is this related to incorrect Kelvin connection?

    3. All ground are same as BAT-

    Thank you for replying my post :)

  • 0 in reply to Chiheon Kwon
    Intellectual 765 points
    >2. I tried it several time, but value was always half of actual battery voltage.

    hmm. what value you read to voltage in hex? High and low byte.. may be you swap MSB and LSB in byte?
    for check connect payload to pack and get 2-3 read from 0x09(0x08) - you should see change voltage value..

    >is this related to incorrect Kelvin connection?

    R7 used for measure current value and direction (charge, discharge, standbay). If you route Kelvin wrong, the chip may be fail measure for current and not normal start..