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BQ20Z655-R1: Current calibration while charging the battery

Eesu
Prodigy 205 points
Part Number: BQ20Z655-R1
Other Parts Discussed in Thread: BQ20Z70, BQEVSW,

I am trying to calibrate the current using SLUA404 - chapter Calibration of bq20z70/z90 Using EV Software - Calibration if cells are attached, and using bqEVSW. It says to discharge the battery with 2A current to calibrate the pack current. Also, in bqEVSW.

The problem is in my board, I need to keep the bq20z655-r1 powered via Pack+ and Pack-, otherwise the communication with bqEVSW is lost. Calibration before connecting cells is even more complicated.

Therefore, can I calibrate the pack current by entering the charging current (positive value) in bqEVSW while the battery is being charged?

  • 0
    TI__Expert 6575 points
    Ideally the current calibration should be done by applying a current across the sense resistor, and not actually charging or discharging.
    Typically on EVM, it can be connected from 1N (Cell negative/VC5) to PACK- .
    I would recommend using a source meter or a precision power supply and current meter so that the current is accurately measured for the calibration.
    Regards,
    Swami
  • 0 in reply to Swaminathan Ramanathan75031
    Prodigy 205 points

    Thanks.

    1. So, it is possible to calibrate using the charging current although recommended is applying a current across the sense resistor and not actually charging or discharging? 

    2. Can I calibrate using the recommended method but instead of having resistors and power supply to simulate the battery, I leave it open and power the IC across pack+ and pack-? Because in our design it not possible to keep communication ON without connecting power supply to the pack± side.

  • 0 in reply to Eesu
    TI__Expert 6575 points
    1. Yes, this is correct.
    2. Yes, you can calibrate while powering the device across Pack+ and Pack- . Typically we don't recommend doing calibrations with cells attached.
    Regards,
    Swami
  • 0 in reply to Swaminathan Ramanathan75031
    Prodigy 205 points

    Hi,

    I managed to setup the board as described in "9.1 Calibration of the board if cells are not attached".  Setup was with the 470Ω resistors and power supply across 4P and 1N. And another power supply across 1N and Pack- with 2A current. Nothing connected to Pack+.

    I can successfully calibrate but the voltage and current values do not change after calibration.

    Measured voltage before calibration = 7826 mV

    Entered actual voltage for calibration = 7860 mV (it is 2S battery pack)

    Measured voltage after calibration = 7826 mV

    Measured current before calibration = -1566 mA

    Entered actual current = -1980 mA

    Measured current after calibration = -1566 mA

    As you can see the current deviation is large. I thought is would change after calibration. Is this normal?

  • 0 in reply to Eesu
    TI__Expert 6575 points
    Hi,
    Please make sure that you are in calibration mode: ManufacturerAccess() command 0x0040, otherwise the calibration values will not be written.
    The easiest way to verify this will be to check the Data flash-> Calibration tab in bqEVSW to see if the values changed after calibration.
    Regards,
    Swami