BQ76920EVM: BQ769x0 Evaluation software show "incorrect voltage value "

Part Number: BQ76920EVM
Other Parts Discussed in Thread: EV2400, BQ76920

Hi Sir,

Our equipment is EV2400 + BQ76920EVM + Power Supply(attached picture) 

We follow SLVU924D bq76920 Evaluation Module User's Guide 2.2.1 AFE Quick start,

8.onnect a 0-V DC power supply capable of 250 mA minimum to the “BATT” terminals and adjust to
approximately 18 V. 

10. Start the bq769X0 evaluation software. The GUI should display. Click on the Scan box to enable
repeated update of the display. The power supply may be adjusted within range of the part to observe
voltage changes in the GUI display Stack V/T/I section.

Please refer to the attached picture.

The Battery Voltage should be 18, not 16.370

The Voltage Cell 1 should be 3.6, not 0.05

The Voltage Cell 2 should be 3.6, not 4.392

The Voltage Cell 3 should be 3.6, not 3.991

The Voltage Cell 4 should be 3.6, not 3.994

The Voltage Cell 5 should be 3.6, not 3.991

Even though we shutdown the system, then boot it again, this fail situation is still the same.

Could you please help us to check what is wrong?

Does it mean the hardware component (near Voltage Cell 1)should be replaced or something?

Thanks!!

Voltage 

  • Hello,

    Your shunts and headers look correct. Double check that all of the cell simulator switches are turned on and clear any faults on the board using the evaluation software. 

    There is not enough detail to know if a component needs replacing. You could check by comparing resistor and capacitor values to the schematic on the EVM user guide. 

    Thanks,
    Caleb

  • Hi Perez,

    Thanks for your reply.

    The cell simulator switched picture is as below,

    Do you think that we should measure and compare the R1~R9 and C1~C6 first?

    wawafish

  • Hi Perez,

    I measure R1~R9 after unplug power.

    R1=0.12

    R2=0.12

    R3=9.915K

    R4=99.79

    R5=99.69

    R6=99.95

    R7=99.68

    R8=74.88 (should be 100)

    R9=74.83 (should be 100)

    Do we need to measure another hardware component?

    Thanks,

    Wawafish

  • Hello,

    It looks like a component of the cell simulator resistor divider may be broken. The voltage that is supposed to be dropped as "Cell 1" is being dropped across all the other cell inputs, which explains the higher voltage reading. 

    Check these resistor values below.

    Thanks,
    Caleb

  • Hi Perez,

    Thanks for your reply, we check the resistor as you mentioned.

    R64 =1000

    R65 =1000

    R66 =199.68

    R67 =199.82

    R68 = 199.46

    R69 = 200.34

    R70 = 99.97(It should be 200)

    Should we need to replace R70 resistor to 200 ohm?

    Thanks,

    Wawafish

  • Hi, 

    Yes, R70 should be a 200 ohm resistor. The smaller value might explain the issue you are seeing because it sets the Cell1 voltage very low (the datasheet has a minimum voltage of 2V for Cell1). 

    Best regards,

    Matt

  • Hi,

    After we remove the R70 resistor, we measure the R70 resistor is 200ohm, if didn't break.

    We find the resistor value is influenced by "S3 76SB07ST" Switch.

    If 7 and 8 connect--------R70 value is 100 ohm

    If 7 and 8 not connect---------R70 value is 200 ohm

    But we need "7 and 8 connect", then R70 value would be 100ohm,

    Do you have any idea why "7 and 8 connect " >> R70 resistor will be changed?

    Thanks !!

    Wawafish

  • Hello,

    I've tested the resistor with 7 and 8 connected and my resistor value is still read as 200 Ohms. It sounds like there might be a short on your EVM somewhere. If you can, I would verify correct behavior on a new EVM.

    Thanks,
    Caleb

  • Hi,

    I provide one clue about this issue.

    The EVM board is all right before.

    After we set the Cell Balance1 register CB5/CB4/CB3/CB2/CB1=1 in bq769x0 evaluation software,

    Then the voltage value is wrong, the resistor is wrong, Even power off and power on again, the issue is still existing,

    Could you please based on this clue to provide us the suggestion to repair our EVM board?

    Thanks!

    Wawafish     

  • Hello,

    Before we try and diagnose the issue on this board could you try replicating the issue on another EVM? The IC may be damaged. Make sure that the other board is functioning properly, and then replace the IC from the damaged board onto the properly functioning one and report the results. Also place the good IC on to the broken board and report the results. 

    Thanks,
    Caleb

  • Hello,

    Thanks for your reply, but we don't have another EVM,

    Do you mean  this IC "BQ7692000PW" for "The IC may be damaged"?

    I search the TI web, I find BQ7692000PW is out of stock.

    Could you please help us to check how we can get the BQ7692000PW IC?

    Thanks.

    Wawafish

  • Hello,

    You can request samples for the BQ7692000PWR IC. These are the same chip.

    Thanks,
    Caleb

  • Hello,

    We get and rework new BQ7692000PW IC in my EVM board today,

    (Normal behavior) We found R66=R67=R68=R69=R70=200ohm when we do not connect S3 switch.

    (Strange behavior) If we connect S3 switch( 1 connect 14, 2 connect 13, 3 connect 12 ,4 connect 11, 5 connect 10, 6 connect 9, 7 connect 8 )

    R67 will be 0.34ohm, R66=R68=R69=R70=190ohm,

    Could you please give us the suggestion how to correct this issue?

    Thanks.

    Wawafish

  • Hello,

    I'm sorry to hear that replacing the IC did not help. This leads me to believe that the EVM board is malfunctioning. If you believe the part was faulty when you got it, you can initiate a customer return. Follow the applicable instructions on this page. https://www.ti.com/support-quality/additional-information/customer-returns.html 

    Otherwise, I would buy another EVM.

    Thanks,
    Caleb