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BQ76920EVM: Can not read Coulomb Counter value

Part Number: BQ76920EVM
Other Parts Discussed in Thread: BQ76920,

I recently did test to measure Cell voltage, Temperature and Charge(or Discharge) Current using bq76920 EVM.

 Referring to the User's manuer of EVM and demo video , I did this procedure.

I connected Power supply to 'Batt' terminals and check whether the parameter value(Cell Voltage1~5, Battery Voltage, Temp Sensor) is correct. everything is ok. 

And I set Configurations like this. 

And I connected Electronic Load to Pack terminals(CC mode)

But I cannot read Coulomb Counter. Coulomb Counter value is always zero at the Evaluation Software. (I did I2C connection correctly.)

(I connected Power supply and Electronic Load like this)

I don't know what should I do.

Please give me advice. 

Thanks.

  • Hi Baek,

    The figures did not come through the post.  Some common issues:

    1. Power must be applied to both the cell input and BATT+, you likely have this since you can read other registers.

    2. The FETs must be on to allow current flow.  You should see current flow in the equipment without the CC.

    3. The CC must be enabled or it will remain 0.  CC_EN will read continuously.

    4. The CC takes 250 ms for conversion.  Since the write from the software is asynchronous it may take 500 ms to have a value available. With manual evaluation you are likely waiting.

    5. CC_ONESHOT does not start again until status is cleared.

    Please check these suggestions and see if it is resolved.

  • Thanks for your reply. 

    The manual says that Power Supply only need to be connect to the 'BATT' channel , not the cell. Doesn't it?

    And I already enabled CC_EN. But bq76920 EVM can not sense any current of Load. 

    I don't know what is the problem.

  • Hi Baek,

    Yes.  If you are using the on board cell simulator it will connect cell 5 to the BATT+. 

    Do you have current flow in the equipment?  Current flow must go through the board to be detected.  With the FETs enabled current should be shown on your power supply and on the load.  The power supply current will be higher since some mA is required to power the cell simulator on the board.

    Be sure the BATT- to PACK- path is not bypassed by equipment grounding.   The current sensing and switching on the BQ76920EVM are both on the low side path.

    If you have current into your load through the board with the CC enabled and no current indication, the board must be damaged.

  • Hi.

    I use .Power Supply. instead of Battery Cell. So I think I don't need cell connection.

    I setup register configuration like this.(load is not connected yet.)

    And then, If I connect the Load(cc mode) to PACK terminal, the register of DSG, CHG is turned to '0'. And any current doesn't be detected.

    *I connected the device as follows.

    (Power Supply -> BATT terminal / Electronic Load -> PACK terminal)

    I need your advice.

    Thank you.

  • Hi Baek,

    With the registers clearing it would seem you are losing power to the board when the load is connected.  Power supplies will typically have a large output capacitor to stabilize the output while the regulation loop adjusts to deliver current.  The capacitor can provide a surge of current to a load.  Supply designs vary however.  Loads will also typically have a significant input capacitance and have an inrush current when connected.  If the current is high enough the BQ76920 could detect it as a short circuit.  What your pictures show however is that the register settings were cleared.  It would seem the part lost power when you connected the load.  It is not apparent how it would still be operating, normally after a reset a boot would be required.  Things to check:

    1. Look at the BATT+ voltage with an oscilloscope when the load is connected.  Look also at CAP1 and DSG.  The BATT+ voltage needs to remain stable during the load connection, the CAP1 should also remain stable and DSG on.
    2. Check that the banana jacks for BATT+ andd BATT- are tight in the board so that there is not a high resistance which could give a power loss.
    3. Be sure the electronic load is disabled when it is connected, this way it has only the input capacitance and minimal current to operate the meter.
    4. Check the current limit on the power supply, be sure it can handle charging the load capacitance and the load current when enabled.

    You might also try to connect as shown in the bottom image, then enable the CHG_ON, then DSG_ON to see if the part will recognize a fault condition and not reset.

  • Hi.

    Thank you for your sincere advice!

    The problem was Power Supply.

    I changed Power Supply and everything is alright.

    Thank you.