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BQ24232: How can we charge two batteries with different ratings.

Hinal Tailor
Prodigy 195 points
Part Number: BQ24232

Hi,

I am using BQ24232 to charge two lithium batteries with different ratings. One is lithium polymer 3.7V/350mAh with charging voltage 4.2V and charging current 150mA and another one is coin cell battery ratings of 3.6V/120mAh with charging voltage 4.2V and charging current 70mA.

I need to know that how can I set resistor value of Riset?

Thanks & Regards

  • 0
    TI__Mastermind 22150 points

    Hi Hinal,

    If you're connecting both batteries at the same time in parallel, the suggestion is to use the lowest charge current for safety (in your case the 70mA). Based on that charge current, you'll need about a 12.7-kOhm resistor. 

  • 0 in reply to Anthony P Pham
    Prodigy 195 points

    Hi Anthony,

    I am using slide switch between two batteries.Condition is that when i will slide switch from right to left then 1st battery will charge which have charging current 150mAh and vice versa.

    I have another query about battery charging capacity. Actually i have read one thing that if i will set 150mA charging current [in my case], and my battery has maximum charging current 120mA then my battery take only 120mA itself not 150mA. I would like to know is this practically possible?

    Best Regards

     

  • 0 in reply to Hinal Tailor
    TI__Mastermind 22150 points

    Hi Hinal,

    To keep cost low and without reducing increasing Iq, it is recommended to use the 70mA resistor value for the ISET pin. 

    It is possible but not recommended as going above the maximum charge current could reduce battery quality (life and capacity). 

    Is the slide switch a manual switch (as in it's not controlled by the system and therefore not monitored all the time)? What is the need for two different and separate batteries?

  • 0 in reply to Anthony P Pham
    Prodigy 195 points

    Hi Anthony,

    Yes, the slide switch is manual, but I want to make logic. Which switching component is best in my case?

    I need to make the system very compact.

    Best regards

  • 0 in reply to Hinal Tailor
    TI__Mastermind 22150 points

    Hi Hinal,

    Without increasing Iq and increasing your BOM, the slide switch is your best case. Otherwise, you'll need components such as external FETs and some way to monitor which battery needs to be charged such as a comparator or an ADC paired with a microcontroller if you don't have one already. 

    What is the application of the two different batteries?

  • 0 in reply to Anthony P Pham
    Prodigy 195 points

    Hi Anthony,

    Not a specific application of two batteries. Actually I want to deliver power from my battery (3.7v/350mAh) to the system and when the battery was not able to deliver power at that time coin cell will deliver. In short, I am using a coin cell for backup purposes only.

    Best regards,

    Hinal Tailor

  • 0 in reply to Anthony P Pham
    Prodigy 195 points

    Hi Anthony,

    Not a specific reason behind the use of two batteries. I want to deliver power from the battery (3.7v/350mAh) to the system But in the case when the battery was not able to deliver power at that time coin cell(3.6V/120mAh) will deliver.

    And I also want to ask you that BQ24232 will do this practically? 

    Best Regards

  • 0 in reply to Hinal Tailor
    TI__Mastermind 22150 points

    Hi Hinal,

    With a single 12.7-kOhm resistor and the manual switch, the BQ24232 will do what you want.