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BQ24650: 8.3.17 Temperature Qualification

Jose
Intellectual 315 points
Part Number: BQ24650

Hi,

If our final option is to disable the thermistor function, and control the charge suspension by firmware, what voltage should we set on the TS pin?

According to our analysis, as Vhtf is 47.5% and Vltf 73.5%, it seems safer to set a voltage in the middle of this value, i.e. approximately 60% of Vref.

The value of 50% of Vref, which would allow us to use two equal resistors, seems too risky as it is close to 48.3% of Vhtf.

Is our understanding correct?

Thanks.

regards

Jose

  • 0
    TI__Mastermind 29932 points

    Hi Jose, 

    Thank you for reaching out!

    From my understanding, you are not using a NTC thermistor on the battery pack, correct? I will look into this and get back to you by Thursday.

    Best Regards, 

    Aya 

  • 0 in reply to Aya Khedr
    Intellectual 315 points

    Hi Aya,

    Thank you for your reply.


    We have a temperature sensor in the battery, but it's not a thermistor, so the control is done by the microcontroller via an ADC pin.


    We just want to disable the temperature control by the TS pin, ensuring that the charge is never suspended by the function associated with the TS pin.

    We must therefore ensure that the correct voltage is applied to the TS pin for the desired purpose.
    In addition, we want to make sure that we have a safety margin for deviations and variations that occur in the circuit.

    regards,

    Jose

  • 0 in reply to Jose
    TI__Mastermind 29932 points

    Hi Jose, 

    Yes, your understanding is correct.

    It would be safer to set the voltage in the middle of  Vhtf and Vltf, i.e. approximately 60% of Vref as you mentioned. It may be risky at 50% due to tolerance/variations. 

    Please let me know if you have additional questions.

    Best Regards, 

    Aya 

  • 0 in reply to Aya Khedr
    Intellectual 315 points

    Hello Aya,

    Thank you for your reply, and I'd like to take this opportunity to ask you another question about the BQ24650.

    We have several projects working with the BQ24650, for different maximum charge currents, and all of them with excellent performance.

    In this new project we have a limitation, in that we can't use 1210 package capacitors due to their height, so we'll have to use 1206 capacitors.

    I'm talking about 10uF - 35V capacitors

    Initially we designed the project with 2 capacitors at the input of the solar panel, and 4 at the output of the battery due to the high charging current.

    As you know, changing a capacitor from a 1210 to a 1206 package means effectively reducing its capacity, so this is a concern.

    Placing 2 pcs. of 10uF-1206 capacitors in parallel for each of the above in package 1210 would be a solution, but it increases the PCB area, and the final cost of the product.

    Of course, we'll have to carry out a test, but before we do we'd like to have a suggestion as to the best solution.

    What would you suggest?

    regards

    Jose

  • 0 in reply to Jose
    TI__Mastermind 29932 points

    Hi Jose, 

    I will look into this and get back to you with feedback on Monday.

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    TI__Mastermind 29932 points

    Hi Jose, 

    Thank you for your patience. 

    The size of the capacitor in this particular case does not have a significant impact on the design since it isn't a high frequency signal.

    I would just suggest making sure the effective capacitance aligns with the recommendations in the datasheet. 

    Best Regards, 

    Aya Khedr 

  • +1 in reply to Aya Khedr
    Intellectual 315 points

    Hi Aya,

    Thank you for your reply and we'll take this information into account for the final design.

    regards

    Jose