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BQ24130: SuperCap: different charger current manner using different batch

Yue TANG
Expert 8515 points
Part Number: BQ24130

Hi, 

       My customer is CM for big e-meter company. they used BQ24130 for super cap and MP with a lot of this device.  but recently, they found a few of new batch devices show different charging manner as below show.

as can see, the blue one customer think it's abnormal.  the charging current first reach to a high level, then drop to the charging current they set, but normal one, the current ramp up from a level to their setting. 

they confirmed the super cap has been discharging to zero before the test. they want to know what may be the issue. thanks.  

 

       

  • 0
    TI__Mastermind 33095 points

    Hello,

    Can you please send a more clear plot that details the current levels at the beginning? This will help me in my analysis.

    Thanks,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    TI__Expert 8515 points

    please see below picture.  Customer mainly concern about the different charge current manner. 

    do you think if it's normal.  they do did AABB switch. the symptom follow device. 

  • 0 in reply to Yue TANG
    TI__Expert 8515 points

    BTW, can you show me a typical charge carve of supercap?  

    1. from their schematic, the charging current should be 320mA, but it shows 210mA, do you think it's normal?

    2.  also , the charging voltage is 11.9V,  according to the settings, I think it should be less than 8.4V( unclear description in datasheet)?

  • 0 in reply to Michael Emanuel35
    TI__Expert 8515 points

    NG board 和OK board Data.xlsx

    Attached is their AABB test data and the data source of the pilot.  

  • 0 in reply to Yue TANG
    TI__Mastermind 33095 points

    Hello,

    Please see "Battery Voltage Regulation" in the datasheet. "Internally, the BAT pin has 717 kΩ to AGND. For output voltage above 4.2 V, but not 8.4 V or 12 V, the user can use an external resistor divider from output to VBAT pin to AGND." This means that the BAT pin is regulated to 4.2 V when you connect the CELL pin to AGND. You then parallel the internal 717 kOhm resistor with your external 68 kOhm resistor for a 62.1 kOhm bottom resistor. Regulating 4.2 V at the BAT pin, this makes the output voltage 11.97 V.

    Also, with CMOD grounded, ISET2 determines the charge current. Your ISET2 current is 252 mA. For a sense voltage of 2.5 mA, I would expect the charge current to be in the range of +/-25% to +/-40% according to the datasheet. Even for the best case, +/-25% puts the charge current range from 189 mA to 316 mA. How are other devices comparing?

    Attached is a charge current profile I captured using a Keithley Bi-Directional Power Supply.

    Thanks,

    Mike Emanuel

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