• TI Thinks Resolved

BQ25708: Can not make it work without battery.

Part Number: BQ25708

Hi all.

I have some trouble with BQ25708 design. Added schematic.

It work good with connected battery. Battery charge ok.

But I can not make it work without battery.
It not started, I have about 1V at Vsys, so my 5V converter not worked.
(but I have 6V at REGN and VDDA)

Chip in default state, no write to registers, only CELL_BATPRESZ pin connected to GND (for case without battery)

Thanks advance.

AnatolyBQ25708RSNT - test board.pdf

  • Anatoly,

    Actually,

    DC/DC should operate whatever battery existed or not. So could you help me to double check below signal?

    1. What is voltage in REGN pin?

    2. Could you measure input voltage, SYS voltage and system current waveform to check?

    From your circuit, I find there some items need to modify.

    3. please change R67/R43/R38/R39 resistor value from 100ohm to 10ohm

    4. Change C12/C29 capacitor value to 47nF

    5. Please keep your input voltage max value is 24V because of our recommend operation max voltage is 24V

    6. what is your JP2/3/4 jumper status?

    Thanks

    Regards,

    Paul

    Texas Instruments

    Battery Charger Solutions

    Please click "This Resolved my issue" button if this post answer your question

  • In reply to Paul Yeh:

    Hi Paul.

    Thanks for reply. We changed resistors and capacitors according points 3 and 4

    But this no have fundamental difference. It still not work as needed. We have tested several boards 

    "1. What is voltage in REGN pin?"

    6V at all boards

    2. Could you measure input voltage, SYS voltage and system current waveform to check?

    Added waveform from good board (Blue - 24V, yellow - Vsys) . At other board it all flat, nothing really moving.

     

     

    "3. please change R67/R43/R38/R39 resistor value from 100ohm to 10ohm

    4. Change C12/C29 capacitor value to 47nF"

    This done

    "5. Please keep your input voltage max value is 24V because of our recommend operation max voltage is 24V"

    Sure

     

    "6. what is your JP2/3/4 jumper status?"

    For waveform that was done. Only JP4 set (battery not connected). Remove JP4 stop oscillating (Goes dead). Move to JP3 - still dead (without battery)
    after add battery, starts up.

    I was thinking that problem can be in 24V source, but even if we using external adjustable power supply (tried 24V and 18V) nothing changed.

    Additional question, what must be default Vsys voltage? (without battery, JP4 set, after reset state)?


    Thanks.

    Regards, Anatoly

  • In reply to Anatoly Dobreen:

    Anatoly,

    For 4cell design and no battery condition, the min system voltage should be 12.288V.

    Do you isolate system loading, just no load condition to see does system voltage ramp up or not?

    BTW, could you also send your register setting log file to me I would like to check your initial setting?

    Thanks

    Regards,

    Paul

    Texas Instruments

    Battery Charger Solutions

    Please click "This Resolved my issue" button if this post answer your question

  • In reply to Paul Yeh:

    Hi Paul. Thanks for help.

    Sorry for delay with reply. We have bought and waited for delivery EV2400 to read and write setup registers at BQ25708.

    Comment. Since I did not found configuration file for BQ25708 at latest BQSTUDIO,

    I used setup for BQ25700A (As I understand it almost same) from this topic https://e2e.ti.com/support/power-management/f/196/t/611912

    I made this setup procedure:

    set max system voltage regulation // REG0x15() = 0x3130H (12.592 V)
    set min system voltage regulation //REG0x3E() = 0x3000H (12.288V)
    set Input current regulation at 1.5A // REG0x3F() = 0x1DFFH
    set charge voltage regulation // REG0x15() = 0x3130H (12.592V)
    set charge current regulation in fast charge // REG0x14() = 0x0400H (1024mA)
    set charge current regulation in LDO mode // REG0x14() = 0x00C0H (192mA)

    and  set bit 5 in "Input current limit in Use" register 0x22  (1 = Adds 1600 mA of input current)

    Please take a look what we have from registers at the moment. Added log files.

    Batt Connected 12.27 J3 output ok 

    * Created: Thu Oct 18 12:41:56 EDT 2018
    *
    * Format: Register Name tab Character,\t Hexadecimal register value.
    * Device: bq25700A
    * BQZ Container: Charger_1_00-bq25700A.bqz
    *
    Charge Option 0 E20E
    Charge Current Register 0000
    Charge Voltage Register 1060
    OTG Voltage Register 0000
    OTG Current Register 0000
    Input Voltage Register 1780
    Minimum System Voltage 0E00
    Input Current Register 4100
    Charge Status Register A010
    Prochot Status Register 0000
    Input Current Limit In Use 4100
    VBUS and PSYS Voltage Read Back 7200
    Charge and Discharge Current Read Back 0000
    Input Current and CMPIN Voltage Read Back 0000
    System and Battery Voltage Read Back 0000
    Manufacture ID Read Back 0040
    Device ID Read Back 007C
    Charge Option 1 0210
    Charge Option 2 02B7
    Charge Option 3 0000
    Prochot Option 0 4A54
    Prochot Option 1 8120
    ADC Option 2000

    23v in Jumper on J4 No Batt No Out

    * Created: Thu Oct 18 12:41:02 EDT 2018
    *
    * Format: Register Name tab Character,\t Hexadecimal register value.
    * Device: bq25700A
    * BQZ Container: Charger_1_00-bq25700A.bqz
    *
    Charge Option 0 E20E
    Charge Current Register 0000
    Charge Voltage Register 3130
    OTG Voltage Register 0000
    OTG Current Register 0000
    Input Voltage Register 1780
    Minimum System Voltage 2400
    Input Current Register 4100
    Charge Status Register A010
    Prochot Status Register 0000
    Input Current Limit In Use 4100
    VBUS and PSYS Voltage Read Back 7200
    Charge and Discharge Current Read Back 0000
    Input Current and CMPIN Voltage Read Back 0000
    System and Battery Voltage Read Back 0000
    Manufacture ID Read Back 0040
    Device ID Read Back 007C
    Charge Option 1 0210
    Charge Option 2 02B7
    Charge Option 3 0000
    Prochot Option 0 4A54
    Prochot Option 1 8120
    ADC Option 2000

    "Do you isolate system loading, just no load condition to see does system voltage ramp up or not?"

    Even with min loading only 5V converter without 5V load (to disconnect this converter I need cut tracks at PCB, I want avoid this at the moment),

    system voltage drop from 12V to 1V, when we disconnect battery.

    Just in case I added one more log.

    log.log

  • In reply to Anatoly Dobreen:

    Hi,

    For BQ25708 GUI, I will ask design team to support.

    From your register content, I saw there is SYSOVP event in Charge Status Register 0x20[4]. And sysovp will turn off charge.

    So could you check your system voltage status?

    Thanks

    Regards,

    Paul

    Texas Instruments

    Battery Charger Solutions

    Please click "This Resolved my issue" button if this post answer your question

  • In reply to Paul Yeh:

    Hi Paul.

    Thanks a lot for help.

    We got a much more complex device than expected initially. Now making experiments with registers settings


    Couple additinal questions :
    - is command "write register" write only one register? sometimes after writing one register, settings for others are changing

    - Chaeger chip became very hot (70-80 deg, it maybe more). Is this correct? As I understand it used only for control power components. Do we need additional heat sink?

    Just in case added sshot for charger PCB area

    PCB in 2 layers. (Real device very big - so we used 2 layers, instead 4. save cost option) 

    R107 was missed in PCB - it soldered manually

    Thanks,
    Anatoly

  • In reply to Anatoly Dobreen:

    Anatoly,

    1. For Write command, it will write all registers once you press the button.

    2. In general, IC should not be thermal source, could you double check MOSFETs and Inductor temperature, may be heat is from these components. Maybe you should need heat sink for these power components.

    3. For this 10ohm resistor, I think manually soldering should be fine. This part is not big current dissipation part.

    4. 2-layer board should be challenge in thermal design.

    Thanks 

     

     

     

    Regards,

    Paul

    Texas Instruments

    Battery Charger Solutions

    Please click "This Resolved my issue" button if this post answer your question

  • In reply to Paul Yeh:

    Hi Paul.

    Sorry for long delay with reply. I working at another projects in another place. (plenty works)

    I think that I found problem (Unfortunately I can not check at real device at the moment)

    It maybe I have problem with 24V supply. Since my supply close to max supply voltage, so when device started it turn on another loads at 24V bus, charger detected overvoltage (transients when loads ON/OFF), and then

    "The charger has fixed ACOV voltage. When VBUS pin voltage is higher than ACOV, it is considered as adapter over voltage. CHRG_OK will be pulled low, and converter will be disabled." (from datasheet)

    Is this mean that charger totally off? So Vsys also off?

    So when I using battery and when charger restarted, Vsys take battery voltage through parasitic diode at battery mosfet and I have stable 5V from Vsys.

    But in case if I try to use device without battery, charger constantly restarted.
    so Vsys - also can not be stable, so my host device at 5V also constantly restarted.

    How do you think can this have sense?

    I want to try decrease supply voltage to 23V and check how it will work without battery. Will check this at real device as soon as I can.

    Thank a lot for help.

    Regards,
    Anatoly

  • In reply to Anatoly Dobreen:

    Anatoly,

    For ACOV condition, BQ25708 will turn off converter then turn on BATFET to discharge.

    And if ACOVP situation is disappeared, BQ25708 will re-start.

    Thanks

    Regards,

    Paul

    Texas Instruments

    Battery Charger Solutions

    Please click "This Resolved my issue" button if this post answer your question

  • In reply to Paul Yeh:

    Thanks for reply. Will check at real device as soon as I can. (then I hope, close topic)

    Additional question from our software developer. "Do TI have any example code for demonstration product with this charger chip?"


    Thanks again.

    Regards, Anatoly