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BQ27530-G1: Discharge termination disable system output

Chris Pettus
Prodigy 100 points
Part Number: BQ27530-G1
Other Parts Discussed in Thread: BQ24161, , BQSTUDIO

I am using the BQ27530-G1 fuel gauge in conjunction with the BQ24161 battery charger.  The SYS output of the BQ24161 is connected to a TPS61236 which regulates the system load to 5V.  While performing the learning cycle I disconnected the supply input to the BQ24161 so that the system would run from the battery until it reached the fully discharge point.  At this point the system begins to cycle on and off which I believe is caused by the battery voltage recovering when the load is removed.

Since this seems like a typical usage scenario where no input is connected and running from the battery that the fuel gauge would disconnect the battery to prevent further discharge.  The SysDown Set Volt Threshold is 3150mV, the SysDown Set Volt Time is 2s, the SysDown Clear Volt is 3400mV and the Final Voltage is 3000mV.  The IT config has Terminate Voltage as 3000mV, the Term V Delta as 200mV and the ResRelax Time as 500s.  The battery is an UltraLife UBBL23 comprised of two 18650 cells in a 1S2P configuration.  The total capacity is 4800mAh with a voltage range of 3000mV to 4200mV and a under voltage limit of 2500mV.

Is there a way to configure the BQ27530 to disconnect the internal FET in the BQ24161 so the BAT input is disconnected from the SYS output until a power source is connected to the input of the BQ24161?

Could this be caused by the fact the fuel gauge has not completed the learning cycle?

Thank you.

  • 0
    TI__Guru* 76230 points
    Hi Chis,

    The bq27530 does not control the charge and discharge fets. All it does is broadcast charging current and charging voltage to the charger. Do you have a bqstudio log files to show this behaviour. The toggling on and off of the fets would not be caused by learning not successfully completed.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 100 points

    Hello Onyx,

    I do have a log file for the discharge cycle which I have attached.  This was a log to upload to the Gauging Parameter Calculator (GPC) tool so it only logged minimal information such as time, voltage, current and temperature.  Around line 7247 you can see the start of communication errors where the board began to power cycle.

    I am not certain that the board turning on and off is caused by the FET turning on and off.

    Reading the datasheet for the BQ27530 it also controls the charge enable and the termination functions of the BQ24161.

    I am not exactly trying to control the FET in the BQ24161.  What I want to achieve is that when the battery reaches the fully discharged level of 3000mV is to disable power to the system from the SYS output of the BQ24161 to prevent further discharge of the battery.  When a power source is connected the output to the system would be enabled and the battery would begin charging.  This seems like a common usage of the BQ27530 and BQ24161, is it possible to configure the Data Flash (Data Memory) of the BQ27530 to achieve this function?

    Thank you.discharge1.log

  • 0 in reply to Chris Pettus
    TI__Guru* 76230 points
    Hi Chris,
    I believe it wouldnt't be too difficult to reproduce the behviour while logging all the registers from the gauge using bqstudio. looking at the registers in addition to a gg file extracted from will help us understand what is wrong with your settings. Perhaps the gauge is getting into a condition where it is getting the charger to turn off and on.
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 100 points

    Hello,

    I am attaching a log file with all the registers enabled and the export of the gg.csv from the data memory.  The log file does not start with a fully charged battery but it does show when the board began to cycle on and off.

    Thank you,

    Chris5001.BQ27530.zip

  • 0 in reply to Chris Pettus
    TI__Guru* 76230 points
    Hi Chris,
    Thanks for sharing the files. I reviewed the logs and i see you are discharging way past your terminate voltage which is set at 3V. You are discharging way down to 2.6V which is even below the min supply voltage for Vregin to support df updates.

    Do you see the same behavior when you discharge to just 3V.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 100 points
    Hi Onyx,

    How would I discharge to just 3V?

    My understanding was the fuel gauge BQ27530 and battery charger BQ24161 would handle the disconnection of the battery to prevent further discharge. In the datasheet for the BQ24161 Section 9.3.6 "Battery Only Connected" it states that if the Battery is less than VBATUVLO the internal battery FET (Q4) remains off and the BAT is high-impedance. Since the BQ27530 is intended to be paired with the BQ24161 how would the configuration be changed to stop discharge at 3V?

    Thank you,
    Chris
  • 0 in reply to Chris Pettus
    TI__Guru* 76230 points
    Hi Chris,
    Your understanding is not correct. The bq27530 doesn't have an inbuilt AFE for controlling fets that is able to cut off discharge when a threshold is reached. The UVLO settings on the charger is fixed and i don't believe is programmable. Your host uC should be intelligent to shut down the system down when SOC reaches 0% and not allow continuous discharge down to 2.5V which is the UVLO of the charger. Alternatively, you could add a secondary level protection device with charge and dicharge fets that will cut off discharge at 3V.

    thanks
    Onyx