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BQ25756EVM: EN_CHG mode stops working

George Triantafillou
Prodigy 50 points
Part Number: BQ25756EVM

Hi hope you are doing well, 

I have been using the BQ25756EVM In the following configuration 

This was working well for the past few weeks but when running some more tests recently in the same configuration I have been unable to charge the battery/ enable charge mode. 

This has been the FW steps I have been taking 

Opens comms

Disable EN_CHG and Watchdog

Configure 16 bit registers ICHG_REG, IPRECHG

Enable  EN_CHG

I have done some basic checks and this is what I have found. 

  • The gates on the switching FETs are constantly low regardless on which mode is activated. 
  • I have performed a diode check on the FETs and all four seem to be functional and in good health
  • A visual inspection of the other hardware components was performed and everything seems okay. 
  • There is to voltage generated on the "OUT" port when the battery is disconnected. 
  • I am able to communicate with the IC (able to read registers and ADC values)

I have played around in your BMS software and have been unable to resolve the issue. 

Would you have any steps/suggestions going forward to further help my debugging process. 

Thank you. 

  • 0
    TI__Mastermind 30785 points

    Hello George,

    Thanks for working with us on this. I have a few questions.

    Is the charger setting any flags or statuses? Can you send me a screenshot of the 8-bit registers?

    What battery voltage are you charging at?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 50 points

    Hi,

    Thank you for the reply. 

    Yes, I recently attempted to use the development kit again and it was semi functional this time (same set up as last time). 

    When I initially turned the development kit on I noticed 49V at the output (this is how we have configured it via hardware) however, it instantly started to deplete as if the capacitors were charged up and were slowly discharging. 

    I then attached the devkit to my PC where I was able to disable both watchdog and EN_CHG. I then configured the current limits and was able to momentarily EN_CHG and see the voltage and current on the output. 

    I tested the following output current limits: 

    2A: Worked 

    1A: worked 

    700mA: worked 

    worked = ran for 1-2min before I stopped the test

    When I attempted to go lower (500mA) It would work for 10-15 seconds then cut out. During this cut out I observed the DRV_SUP pin fault flag and 0V across the output. 

    I was then unable to get the device to charge with any configurations. 

     

    Further more through out this testing I would regularly enable the ADC and the input current value would be roughly 2 times the real value and the output current would be around 75% the real value. 

    Apologies I did not take a screenshot of the registers but they all look correct except for the DRV_SUP. 

    Thank you, 

  • 0 in reply to George Triantafillou
    TI__Mastermind 30785 points

    Hello George,

    Thanks for working with this. I have a few questions for you.

    What type of load are you using and what's the voltage set to?

    When the 500mA current cuts out, does it come back on after a while? This may be due to the charger reaching the termination current.

    When the issue does happen, can you click "Read Registers" and then take a screen shot of the 8-bit registers in the BQZ file? This will be very helpful to me.

    Best Regards,
    Ethan Galloway