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BQ24125: 3-cell battery charging issue

Ravi Jindal
Prodigy 50 points
Part Number: BQ24125

Dear TI community,

To charge 3-cell battery I'm using BQ24125 BMS IC, When I given 12 V supply using power source, LED given on PG (power good status) pin is continuous ON but  other 2 LED's given on STAT1 (charge in process) & STAT2 (charge is done) have no response means my battery is not charging(checked current). Kindly review components value of attached schematic circuit, if any changes please let me know.

regards.

  • 0
    TI__Mastermind 40305 points

    Hello,

    Having both STAT1 and STAT2 off means that either: "Charge suspend, timer fault, overvoltage, sleep mode, battery absent."

    Can you please measure your TS voltage and confirm if it is in the right range?

    What is the battery voltage you are measuring on the BAT pin?

    You have a voltage regulation of 12 V, however your input is 12 V. You may not be able to fully charge the battery with a 12 V input because you need headroom for the output given this is a buck converter topology.

    Can you please capture a waveform of the BAT pin to verify the battery detection behavior?

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.

  • 0 in reply to Michael Emanuel35
    Prodigy 50 points

    Hi,

    I have connected Battery which is 11.1V 2600 mAh rating. When I am calculating the Voltage across TS & VFB is-

    TS voltage is 2.12V & VFB is 2.59V.

    Input Supply= 12V

    During charging time both LED's STAT1 & STAT2 are off and current is showing 0.02A. means my battery is not charging when supply and battery both are connected.

    Pls check and response maybe I need to changed registers value.

    Thanks & Regards.

  • 0 in reply to Ravi Jindal
    TI__Mastermind 40305 points

    Hello,

    Can you please check your resistive divider for the FB pin? The regulation for this pin is 2.1 V and you are above regulation considerably causing potential overvoltage. This pin needs to read 2.1 V when the battery is fully charged. Please adjust the resistor divider to allow this condition.

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.

  • 0 in reply to Michael Emanuel35
    Prodigy 50 points

    Hi,

    As per your suggestion I changed the resistor divider value RF1= 47K & RF2 is 7.5 K. In this condition

    Condition 1:

    When supply is ON and battery is not connected then-

    VFB: 0.6V

    TS= 2.13V

    ISET1= 057V

    ISET2= 0.42V

    OUT voltage= 0.11v

    Status of PG LED is ON.

    Condition 2: 

    When  supply (12V) and battery (11.1V 2600 mAh)  both are connected then:

    VFB pin is 2.15V.

    TS = 2.13V

    ISET1 & IST2 both are 0.671V

    OUT voltage= 11.65V

    Status of PG LED is ON,

    Status of both LED's STAT1 & STAT2  are OFF

    In this scenario current is showing 0.02A. means still my battery is not charging.

    Pls check and response maybe I need to change something else.

    Thanks & Regards.

  • 0 in reply to Ravi Jindal
    TI__Mastermind 40305 points

    Hello,

    I think we need to review the setup as something does not seem right. With a 47 kOm upper resistor and a 7.5 kOhm lower resistor on the VFB pin the charge regulation voltage is 15.26 V. However, if we back calculate from the VFB pin, the battery voltage would read 15.623 V. Can you capture a waveform of the input voltage, OUT voltage, BAT voltage, and charge current when these are happening?

    There are several key things here:

    1. You cannot have a charge voltage regulation greater than the input voltage (12 V) as this is a buck converter topology.

    2. Your battery is potentially overvoltage, (VFB>2.1V) causing both STATx pins to go off.

    3. You need to set the charge regulation of the charger such that VFB is 2.1 V when full charged. In other words, if you want 11 V charge voltage a 47 kOhm upper resistor and a 11.09 kOhm resistor would do the trick. The equation is: VREG = 2.1*(1+Rupper/Rlower). This charge voltage regulation is the maximum voltage you would place on the battery, ie when it is fully charged.

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.

  • 0 in reply to Michael Emanuel35
    Prodigy 50 points

    Hi,

    As per your suggestion I just changed the resistor divider value R1 = 47K & R2=11K now-

    VFB pin is 2.8V.

    TS = 2.4V

    ISET1 & IST2 both are 0.671V

    OUT voltage= 10.65V

    Status of PG LED is ON, other two LED's are OFF.

    Regards.Battery Voltage during charging time

  • 0 in reply to Ravi Jindal
    TI__Mastermind 40305 points

    Hello,

    Please help me to understand the battery voltage. If the upper resistor is 47k, the lower resistor is 11k, and the FB pin is 2.8 V, this means that the battery voltage is 14.76 V. This is overvoltage as your programmed battery voltage is 11.07 V.

    In addition, your TS bias is not correct for charging operation. If you have a TS voltage of 2.4 V, the TS% is 2.4/3.15*100% (3.15 is VTSB). This percentage is 76% which suspends charge. Please bias your TS pin appropriately for the thermistor and desired temperature range.

    Can you  please capture a waveform of the input voltage, OUT voltage, BAT voltage, and charge current when these are happening?

    Thanks,

    Mike Emanuel