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  • TI Thinks Resolved

BQ24130: BQ24130 charging problem

Part Number: BQ24130

Dear all,

I met a problem when using BQ24130 in charging for a Super capacitor.The output charging current does not meet the current I set. For example,when CMOD is set to low,and Viset2=2V, the sense resistor is set to 100mΩ,the theoretical charge current should be 200mA, but the The actual measured value is only 160mA.Change  sense resistor to 50 mΩ,the theoretical charge current should be 400mA, but I only get 273mA fron the output!!! and the same problem occurs in the fast charge mode.could you give me some suggestion?

  • Hi,

    Please make the following changes:
    1. Add 2x10uF + 1uF caps to the output after R136, you can remove C81
    2. Please take into account that the BAT pin has a typical resistance of 717kohm to GND, this may change your regulation point for the super cap
    3. Make resistor divider from VREF to TS such that TS = 2V
    4. ISET1 must be above 100mV for the charger to work properly, please modify resistor divider from VREF

    Let me know if this changes anything.

    Regards,
    Steven

    Battery Charger Solutions

  • In reply to Steven Bangdiwala:

    Hi steven,

    I have double checked all according to suggestion  you give to me ,but nothing changed!1

    could you give me some futher comments?

    thanks!!!

  • In reply to user5102208:

    Hi,

    What is the charging current when you made the changes, did it move closer to the regulation point or farther?

    Also, if you could, attach waveforms for PVCC, AVCC, SRN and VREF. There may be noise or stability issues.

    Regards,
    Steven

    Battery Charger Solutions

  • In reply to Steven Bangdiwala:

    Hi,

    We have changed all your Suggestions before telling you.

    The waveforms for PVCC,AVCC,SRN and VREF is as follows:

  • In reply to user5361587:

    Can you show the new schematic? What are the numbers for charging current that you are getting after the changes?

    Regards,
    Steven

    Battery Charger Solutions

  • In reply to Steven Bangdiwala:

    Hi steven,

    The  sense resistor is 50 mΩ,the theoretical charge current should be 400mA, but I only get 270mA~280mA from the output!!!

    The new schematic is as follows:

  • In reply to user5361587:

    When the COMD pin is connected to VREF, R138 and R139 are changed to 75K and 23K, the theoretical charge current should be 774mA, but I only get 430mA from the output!!!
  • In reply to user5361587:

    Hi,

    What is your Super Cap value? How much voltage do you want to output?

    Also, try lowering your inductor value to 6.8uH or 4.7uH.

    Regards,
    Steven

    Battery Charger Solutions

  • In reply to Steven Bangdiwala:

    Hi,

    The Super Cap value is 165F,5.5V. I have changed the output voltage  to 5.5V ,but when the voltage of the Super Cap is 5V, the charging current drops to 0 mA.

    I have also changed the  inductor to 4.7 uH ,but nothing changed,the charging current is also 277mA. 

    ,

  • In reply to user5361587:

    Hi,

    For 5.5V regulation on the Super Cap, you will need to change R115 to 267kohm. This will give you close to 5.5V regulation, taking into account the internal resistance of 717k from BAT to GND.

    I don't see what else could affect your charging current, unless you have a very long cable from the output to the super cap, which will increase your ESR and could hit regulation point much faster.

    Could you show me a plot of PVCC, AVCC, SRN and SW when you are charging up the cap?

    Regards,
    Steven

    Battery Charger Solutions

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