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BQ25505: BQ25505 BMS chip Battery protection availability

Rajan
Intellectual 270 points
Part Number: BQ25505
Other Parts Discussed in Thread: BQ24040, BQ24210, BQ25792, BQ25798

Hi,

We have chosen BQ25505RGR BMS chip for our project.

Planned to use Rechargeable Battery (18650 series) as Lithium-Ion and Non rechargeable Battery as Lithium Thionyl Chloride (3.6V).

Whether Lithium-Ion Rechargeable Battery itself required Protection circuit or BMS chip (BQ25505) will take care of Battery protection?

Please suggest accordingly need to choose the Lithium-Ion Rechargeable Battery.

(Batteries type planned to use as PCB mountable)

Also let me know what is the maximum Solar watts will support the BQ25505 BMS chip.

Thank You,

Rajan

  • 0
    TI__Guru*** 149885 points

    Hi Rajan,

    The BQ25505 constant voltage (CV) charge operation protects against battery overvoltage and the PFET between VSTOR and VBAT prevents over discharge below a fixed voltage of ~2.2V.

    You can use either battery type and simply change the VBAT_OV resistors for either 4.2V for LiIon or 3.6V for LiTCh.

    Since this is a boost only charger, the input voltage must always be below the output voltage so the panel's MPP should be below VBAT_OV setting (4.2V or 3.6V).  Also the charger's peak inductor current is about 220mA so no need for the panel's output current to be above that value.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 270 points

    HI Jeff,

    Thank you for your information.

    Can I connect External Power supply source (5VDC) to the BMS's Solar input point 'VIN DC' with series diode for charging the Rechargeable battery, If sun light not available long period?

    Which Battery type (Li-Thionyl Chloride 3.6V / Li-Ion Manganese 3V) is preferable for Non rechargeable battery requirement? 

    Rechargeable battery which type (Li-Ion / Li- polymer) is good for RF application, Outdoor and long life?

    Thank you,

    Rajan 

  • 0 in reply to Rajan
    TI__Guru*** 149885 points

    Hi Rajan,

    You cannot connect a 5V DC input to VIN_DC because the charger can only boost up a lower voltage to the final charge voltage.  If you want to charge from 5V source, you would need a second battery charger with its output connected in parallel with the BQ25505 VBAT_SEC pin. 

    TI does not make battery recommendations.  From a voltage standalone, I recommend 3.6V for non-rechargable battery over 3.0V.

    Most customers use LiIon but LiFePO4 is more robust for some outdoor applications.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 270 points

    Hi Jeff,

    Thank you for your suggestion,

    Can you please suggest second battery charger part details for 5V DC Input.

    Instead of 5V, can I reduce to 4V and use same BMS  BQ25505 'VIN DC' Pin?

    But the datasheet mentioned VIN(DC) Max. is 5.1V.

    Please find interface block diagram for your reference.

    Thank you,

    Rajan

  • 0 in reply to Rajan
    TI__Guru*** 149885 points

    Rajan,

    The battery charger is a boost only charger so the MPP voltage at VIN_DC must be below the VBAT_OV.  If VBAT_OV is below 4V then you can set VIN_DC =4V.

    If you want to add a 5V charger, I recommend a linear charger like BQ24040.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 270 points

    Hi Jeff,

    Thank you for your continuous support,

    Whether BMS BQ25505 will enable the Primary Non rechargeable Battery 'VB_PRI_ON', if solar power not available and Secondary rechargeable battery drained / low voltage ?

    Is it available any other BMS chip with Solar and 5V input provision?

    Thank you

    Rajan

  • 0 in reply to Rajan
    TI__Guru*** 149885 points

    Hi Rajan,

    If the VBAT_OK circuit, power by VSTOR>1.9V, senses that VBAT <VBAT_OK threshold, then VB_PRI_ON goes low to turn on its related PFET, regardless of VIN_DC applied or not.

    The BQ24210 is a linear regulator charger with MPP function.  It is buck only which means VIN must be greater than VBATREG.

    We do not market other chargers exclusively for lower panel solar panels.  If your solar panel is higher power (ISC>>200mA) and your battery capacities are in than that same range or higher, then you might consider the soon to release BQ25798, which is a BQ25792 with MPP feature added.  

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 270 points

    Hi Jeff,

    Could you please share BMS BQ25505 function Flow chart?

    What will be the status of 'VB_PRI_ON' pin, If SEC_BAT not available / fully drained?

    Thank you,

    Rajan

  • 0 in reply to Rajan
    TI__Guru*** 149885 points

    Hi Rajan,

    There is no flowchart available other than datasheet figure 12 page 14.  The gate drive signals following VBAT_OK = /VB_PRI_ON, with /VB_SEC_ON being the inverted version.  There is a slight delay between the 2 signals to achieve make before break as shown on the same page.

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Intellectual 270 points

    Hi Jeff,

    Since BMS is a boost charger, Could you please let me know what is the minimum and maximum output voltage of the BMS.

    I planned to use Buck Boost converter for getting 3.3V for my application.

    Thank you,

    Rajan

  • 0 in reply to Rajan
    TI__Guru*** 149885 points

    Hi Rajan,

    minimum VBAT_OV = VMPP+0.1V

    maximum VBAT_OV = 5.5V.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 270 points

    Hi Jeff,

    Is there any limitation is there for Battery capacity (Rechargeable and Non rechargeable) using BQ25505 BMS.

    What is the Maximum battery capacity (Ah) will support support BQ25505 BMS for PRI_BAT and SEC_BAT. 

    As per datasheet BQ25505 BMS support 510mW Solar power (PIN). If I use <200mW solar cell, what will be the Impact?

    What type Solar panel is preferable for BMS? we have chosen Monocrystalline (Voc = 4.15V). is it okay?

    Please provide your suggestion.

    Thank You,

    Rajan,

  • 0 in reply to Rajan
    TI__Guru*** 149885 points

    Hi Rajan,

    There is no embedded capacity constraint.  However, practically, with max input power being 510mW, the charge current will be low and time to full charge increases as capacity increases.  Also, the FET between VBAT_SEC and VSTOR being almost 1 ohm resistance, so if there is a load on VSTOR that pulls a large current from the high capacity battery, there will be a big voltage drop.

    With only 200mW input power, the max output power is 200mW*efficiency.  The max charge current is 200mW*efficiency/VBAT_SEC where VBAT_SEC will likely sit between 3.6-3.8V during most of the charge cycle until stopping at 4.2V.  You can pull efficiency numbers from the datasheet efficiency curves for your MPP voltage and current.

    As long as VBAT_OV < VMPP=4.15*80%, then I see no issues. Monocrystalline is quite commonly used.

    Regards,

    Jeff