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Selection NTC for bq24650 EVM

Nahuel Hanuch
Prodigy 70 points
Other Parts Discussed in Thread: BQ24650

Hello,

I'm from Argentina, I'm working with a group of people in the design of the energy power system of a micro satelite. We have choosen the bq24650 EVM to do some test considering the posibility to send the bq24650 to the space.

I read the note " Maximum Power Point Tracking With the bq24650 Charger " in the selection of the ntc, to put the B-value, depends on the range of temperatures to linearize. The range we have is too wide ( -50ºC / 150ºC). We thought to use the " NTC 151-243 100k ". Could you recomend a solution to the wide range or another thermistor?
Another question, we have checked that the range of temperatures in space is acceptable for the bq24650, we want to know a little more about the radiation problems or even if you have the same bq24650 with more quality .

Thanks

  • 0
    TI__Genius 13700 points

    Hello Nahuel,

    I am going to address your device rating question first. The parametric search tools available on TI.com can be used to filter your device selection based on operating temperatures and the device rating. Hi-Rel ratings are greater than that standard catalog rating but in there are no Space qualified chargers.

    I would recommend using the temperature rating filter first to explore what your options are since the only Hi-Rel parts are available for Lead Acid and not optimized for solar applications.

    The important focus for designing your thermistor circuit is that it operates linearly within the charging range for the battery. When the NTC indicates that the system is outside of the acceptable temperature operating range the linearity no longer matters because the NTC information will not be used by the chip when it is in temperature suspend until you return to the linearized region which should cover the charging range for the battery and the operating range for the chip.

  • 0 in reply to Ryan May
    Prodigy 70 points

    Thanks very much for your answer, I have another problem, when I used the spreadsheet when I used the same values as the example, Rp and R5 match the value in the example but not Rs. Also the excel do not show me the graphs I already prove in office 2003 and 2007. I hope you understand my english   

  • 0 in reply to Nahuel Hanuch
    TI__Genius 13700 points

    Hello Nahuel,

    I searched around the pages for this device and its EVM but I have not been able to find the EXCEL document you are talking about.

    Could you post a link to the design tool?

  • 0 in reply to Ryan May
    Prodigy 70 points

    Hello Ryan,

    Yes ofcourse, the excel program is in the next link: http://www.ti.com/product/BQ24650/toolssoftware , In SOFTWARE it is called "MPP Tracking with bq24650 and NTC Thermistor".
    The example I'm refering to is in the next link: http://www.ti.com/product/BQ24650/technicaldocuments, called:

    Maximum Power Point Tracking With the bq24650 Charger. (Rev. A)

    I couldn't get the graph excel works, and the results of the resistor as a I mentioned before are not the same as the example.

    Thanks very much, I hope you could help me!

  • 0 in reply to Nahuel Hanuch
    TI__Genius 13700 points

    Hello Nehuel,

    To help me follow exactly what you are seeing and to simplify communication could you save a copy of the EXCEL worksheet with your system parameters and post it to this thread so that I can work with your system information.

  • 0 in reply to Ryan May
    Prodigy 70 points

    Ryan,

    Hello, I will send you the excel with the same values in the example I send you before and you could check that Rs is not the same. Also attached two pics of an error I have when I put "calculate resistor values".

    6445.Bq24650 NTC Cal.xls

  • 0 in reply to Nahuel Hanuch
    Prodigy 70 points

    Hello Ryan,

                         I couldn't use the spreadsheet excel, could you calculate the resistor and the graph with this values in the picture:

  • 0 in reply to Nahuel Hanuch
    TI__Genius 13700 points

    Hello Nahuel,

    Sorry for the delay.

    Here is a screen capture of the excel spreadsheet after I ran it with the values you provided above.

  • 0 in reply to Ryan May
    Prodigy 70 points

    Hello Ryan,

    Me again, sorry I do not want to bother you anymore!. Thanks a lot for the results It will help me a lot!. A last doubt, in which version of windows are you running the spreadsheet?, and in what version of office?

    Thanks again!

  • 0 in reply to Nahuel Hanuch
    TI__Genius 13700 points

    Hello Nahuel,

    No worries. I am running Windows 7 with Office 2010.

    Let me know if there are any other questions.