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BQ24192: SYS Voltage (Vsys) is going down to BAT Voltage (Vbat)

Harikumar Namboothiri
Prodigy 50 points
Part Number: BQ24192

Hi Team,

I'm using BQ24192 for one of my projects as the main PMIC. Please help me to find a solution for the below described problem. 

I'm giving an input of 5V without a battery installed and I'm getting a Vsys voltage of 4.1V. When I'm installing a battery to the running board, the Vsys is suddenly going down to my battery voltage Vbat (I used a battery with 3.8V) and starts to charge the battery. As the battery charges, the Vsys is also increases up to 4.1V.

Now, If I increase the input voltage to 9V, then I'm getting the Vsys 4.2V instead of the battery voltage and battery charging continues up to full as expected.

  • Is there any input voltage threshold to get the 4.3V output from SYS pin?
  • Why I'm getting the battery voltage as SYS voltage when powering with 5V supply with battery installed?
  • Why I'm getting 4.1V without the battery where the specified output voltage should be 4.36V?
  • 0
    TI__Mastermind 26645 points

    Hi Harikumar, 

    Thank you for reaching out via E2E. Please see my comments on your questions below. 

    Harikumar Namboothiri said:
    I'm giving an input of 5V without a battery installed and I'm getting a Vsys voltage of 4.1V. When I'm installing a battery to the running board, the Vsys is suddenly going down to my battery voltage Vbat (I used a battery with 3.8V) and starts to charge the battery. As the battery charges, the Vsys is also increases up to 4.1V.

    This is the expected operation of the BQ24192. Please refer to section 9.3.2.1 on page 16 of the datasheet for explanation of the Narrow VDC architecture used on this device. You observe Vsys at 4.1V with no battery installed because charge is not disabled. If you were to disable charge Vsys would be regulated above the Vsys_min setting (default 3.5V). 

    Harikumar Namboothiri said:
    Now, If I increase the input voltage to 9V, then I'm getting the Vsys 4.2V instead of the battery voltage and battery charging continues up to full as expected.

    This is not the expected operation for this device. I do not observe the same behavior when testing the BQ24192 in lab. With input = 9V Vsys follows the battery voltage as expected. Please help to double check your test results. 

    Harikumar Namboothiri said:
    Is there any input voltage threshold to get the 4.3V output from SYS pin?

    The SYS pin regulation voltage is not related to the input voltage. It will be regulated above Vsys_min (maximum setting 3.7V) when battery is below Vsys_min threshold, and rise up to approximately the charge voltage limit (VREG setting) as the battery voltage increases due to charging. 

    Harikumar Namboothiri said:
    Why I'm getting the battery voltage as SYS voltage when powering with 5V supply with battery installed?

    This is explained in the datasheet section referenced above. When Vbat is above Vsys_min SYS voltage will be the Vds of the BATFET above battery voltage. 

    Harikumar Namboothiri said:
    Why I'm getting 4.1V without the battery where the specified output voltage should be 4.36V?

    SYS pin voltage will only be regulated at 4.36V when battery is fully charged or close to fully charged and VREG setting is 4.36V. You are not able to set SYS pin voltage to always be 4.36V on this device.

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 50 points

    Hi Garrett,
    I'm getting Vsys of 3.6V with a 5V adapter input and with battery installed (Battery voltage is 3.1V).
    I don't understand why I'm getting a 3.6V in Vsys even after the power is supplied from adapter. I think it should give an output of 4.2V in Vsys with battery charging. If I'm wrong, please correct me.
    Also, If I increase the power to 9V, my Vsys is also increasing (Here, Vsys is 3.8V with 9V input, and 3.1V battery). Why is this happening?
    I've tested on two ICs and the results are same for both.

    Regards,
    Hari

  • 0 in reply to Harikumar Namboothiri
    TI__Mastermind 26645 points

    Hi Hari, 

    Harikumar Namboothiri said:
    I think it should give an output of 4.2V in Vsys with battery charging. If I'm wrong, please correct me.

    This is incorrect. As previously explained in my response above Vsys at 3.6V is expected with a 5V adapter and battery voltage at 3.1V. Datasheet states Vsys is regulated approximately 150mV above the SYS_MIN setting when battery voltage is below the minimum system voltage setting. 

    Harikumar Namboothiri said:
    Also, If I increase the power to 9V, my Vsys is also increasing (Here, Vsys is 3.8V with 9V input, and 3.1V battery). Why is this happening?

    I do not observe the same behavior testing on multiple devices. When the only thing changed in test setup is VBUS 5V vs 9V I observe no difference in the Vsys voltage. With all registers in default configuration I measure Vsys = 3.65V with both 5V and 9V input. 

    In your testing is the minimum system voltage setting potentially being changed? SYS_MIN setting is located in REG01 bits [3:1]. Where on the board are you measuring VBAT and VSYS? Please ensure you are measuring as close to the IC as possible to have accurate measurements.  

    Best Regards,

    Garrett