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BQ25616: System Power ON issue

Part Number: BQ25616

Hi,

We are using BQ25616JRTWR to manage battery supply (Li-ion Batteries 3 x 3.7V 2200mAh).

The BMS output is connected to a PMUX (TPS2115ADRBR) which is configured for auto selection of two power supplies (BMS

output, VBUS(from Mini USB-B)). OUT from the PMUX is further provided to a Buck Boost Converter (TPS63020DSJR) which supplies 3.3V to power-up our system. 

On average battery voltage, current from battery are 3.69V, 40mA respectively. When battery is connected to BMS, it delivers around 3.65V 15mA which is not sufficient.

Our minimum system requirement from BMS is 3.3V 32mA.

Please find attached document, Our circuit

Also please explain why BMS is limiting more current from Battery? How to overcome this?

  • Hi,

    We will check and get back to you.

    Thanks,

    Ning.

  • Hi,

    Thanks for your response. 

    I would like to increase the output current. But it is below par for our system.

    Waiting for your feedback.

    Thanks,

    Jegan.

  • Jegan,

     

    What are the operating conditions such as VBUS (voltage at VBUS pin), IVBUS, VBAT (voltage at BAT pin), IBAT, VSYS, ISYS when you think the BQ25616 works abnormally?

     

    Thanks,

    Ning.

  • Hi Ning,

    output we observed at SYS(which is denoted as SYSTEM_PWR in our schematics) as, 

    voltage at BAT, SW, SYS are at desired level.

    when current at BAT is 25mA, current from SW is 15mA. 

    How to increase output current?  with our existing schematics what are the minimal changes that I need to do?

  • Hi,

    What voltages are "desired level"? What are the operating conditions such as VBUS (voltage at VBUS pin), IVBUS, VBAT (voltage at BAT pin), IBAT, VSYS, ISYS when you think the BQ25616 works abnormally? It is hard to debug if there's no charger operating conditions.

    Thanks,

    Ning.

  • Hi,

    Apologies for the miscommunication.

    The operating conditions are

    VBUS = 0V,

    IBUS = 0mA,

    VBAT = 3.6 to 3.7V,

    IBAT = 25 to 35 mA,

    VSYS = 3.5 to 3.7V,

    ISYS = 15 to 20mA.

    Thanks,

    Jegan.

  • Jegan,

    Referring to 9.3.2 Device Power Up From Battery Without Input Source on the d/s, if only the battery is present and the voltage is above depletion threshold (VBAT _DPLZ), the BATFET turns on and connects the battery to the system. So the battery discharge current is dependent on the SYS load current. The BATFET between BAT and SYS will not limit the battery discharging current unless IBAT > ISYS_OCP_Q4 (9A minimum). Please check the battery itself, the SYS load and other components on the circuitry.

    Thanks,

    Ning.

  • Hi Ning,

    Thank you so much for your response.

    We are using Three Li-ion Batteries 3.7V 2200mAh in parallel connection for this BMS.

    Is it the right combination? if not please suggest a suitable battery source with ratings and specifications for this BMS circuit (BQ25616JRTWR)?

    Thanks,

    Jegan.

  • Jegan,

    It is ok to use a single-cell charger to charge multiple cells in parallel as long as the cells have built-in protection and may disconnect bad cells automatically. 

    Thanks,

    Ning

  • Hi Ning,

    We would like to add a note to this.

    While providing supply using batteries as mentioned in the above conversations, the system did not power up. So, we tried supply (5.12V, 0.5A) via VBUS in BMS. We did not even get output on SYS pins.

    After that, we bypassed the BMS device and used the batteries to power our system directly. The System powered up.

    What might be the cause of this?

  • Hi,

    We will check and get back to you.

    Thanks,

    Ning.

  • Hi Ning,

    Waiting for your inputs.

    Thanks,

    Jegan

  • Jegan,

    If you shut down the charger completely (i.e. remove both VBUS and VBAT, no power on the charger) then re-apply VBAT or VBUS, does SYS have any output voltage?

    Thank you very much,

    Ning.

  • Hi Ning,

    As per your recommendation, we removed and re-applied the VBAT. when VBAT = 3.712V; VSYS=3.681V but still system is not powered up.

    Thanks,

    Jegan

  • Jegan,

    The VSYS has 3.681V output supported by the battery. Please connect VSYS to an external resistor load and see if it works normally.

    Thanks,

    Ning.

  • Hi Ning,

    Sorry for the belated response.

    Please see below table for the observations for loads connected to BMS,

    Battery: 3 x 3.7V 2200mAh (Parallel connection)

    VBAT (V)

    Load (Ohms)

    Load Current (mA)

    VSYS (V)

    3.755

    7.5

    289.6

    2.069

    3.756

    15

    168.7

    2.541

    3.756

    30

    101.1

    3.028

    3.756

    60

    55.9

    3.361

    Please revert your feedback. Also please explain what will be the load's impact on BMS(BQ25616JRTWR) output current?

  • Hi,

    Will get back on the next business day.

    Thanks,

    Ning.

  • Hi Ning,

    I would like to add a note to this.

    We have not yet connected NTC thermistor to TS pin. 

    Can it be the reason for decrease in load current?

    Thanks,

    Jegan.

  • Jegan,

    In both charge and boost modes, NTC fault will impact on the charger operations. Please refer to 9.3.7.4.2 Hot/Cold Temperature Window During Charging Mode (BQ25616) on the d/s for the details.

    Please also check if the STAT pin blinks at 1 Hz due to any fault. Please refer to 9.3.8.2 Charging Status Indicator (STAT) on the d/s for the details.

    Thanks,

    Ning.

  • Hi Ning,

    What is the impact of charge suspend fault (NTC fault)?

    Please give a detailed explanation.

    Thanks,

    Jegan.

  • Hi Jegan, 

    The TS will use the thermistor to monitor the battery temperature and perform JEITA or Hot/Cold. The NTC when at fault will affect the charge current, on the case when the temperature is hot or cold the charge will be suspended to protect the battery pack. Please connect a 10-kohm resistor to the TS pin if the TS function is not needed or unused. Also if the STAT pin is blinking at 1Hz that would indicate there is an active fault.  

    For a more detailed explanation of how it works on the BMS you can refer to section 9.3.7.4 of the datasheet. A more in-depth app-note detailing JEITA can be found here: https://www.ti.com/lit/an/slyt365/slyt365.pdf

    Regards, 

    Arelis G. Guerrero 

  • Hi,

    I'd like to show my gratitude to you both Ning & Arelis G. Guerrero for your wonderful assistance.

    Thanks,

    Jegan.