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BQ24030: Charging through USB

Timz
Prodigy 100 points
Other Parts Discussed in Thread: BQ24030

Hi,

If we set ISET2: High & PSEL: Low, USB should provide 500mA current to the circuit. I was wondering how this current will be distributed among 1A Load and Li-ion Battery (3.7V).

Now that AC is disconnected, the battery should be charged at ISET2 rate, right? So, what would be the situation of the Load at this stage?

I've tried testing myself but the results have been erratic, so far.

Kindly, respond.

  • 0
    TI__Genius 13700 points

    Hello Sy,

    If you set your input current limit to 500mA and your load requires 1A then the device will be in supplement mode constantly. You design case will need a much higher input current limit in the case of wanting to continue to charge your battery while your load is consuming 1 A.

    The AC input can be set to the higher input current limit so you are most likely seeing the battery charge when the AC adapter is attached but once it is removed the USB input current limit takes over causing all of the power from the USB and some of the battery power to be used for running the load.

    If you are trying to set the charging current that is accomplished by the ISET pin. This will let you explicitly set the rate that you want the battery to charge. The input current limit you are running into is to protect your source.

  • 0 in reply to Ryan May
    Prodigy 100 points

    So, I should not use such a heavy Load during USB mode, only then will I be able to drive the Load as well as charge the battery?

    Also, is ISET1 charge rate applicable only in AC mode? 

  • 0 in reply to Timz
    TI__Genius 13700 points

    Hello Sy,

    The ISET 1 sets the charging current for the AC adapter only but it sets the termination current for both the AC adapter and the USB input. The reason for this is because the USB current limit is usually lower than the charging current set by ISET1 so that the charge current is typically reduced to match the USB current limit to ensure the input voltage does not droop.

    What is the charge current that you have set with ISET1?

    Yes, if you want the battery to charge when you have the USB input current limit set to 500mA you will need to reduce the load current.

  • 0 in reply to Ryan May
    Prodigy 100 points

    I set RSET at 1.22kohm, which gives me around 850mA charging current.

    Can you also elaborate whether KSET and VSET are randomly selected, or not? Because we have no control over it.

  • 0 in reply to Timz
    TI__Genius 13700 points

    Hello Sy,

    They are not randomly determined but they are subject to tolerances that are influenced by the output current.

    Looking at Pg. 5 of the datasheet with the charging current you selected the for the BQ24030 the Kset value should be about 425 with a tolerance of about +-5%.

    Hopefully that answer your question otherwise let me know is there is anything else that you are curious about.

  • 0 in reply to Ryan May
    Prodigy 100 points

    Thanks for all your help.