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BQ24105: temperature protection

Randy Chen
Intellectual 1920 points
Part Number: BQ24105
Other Parts Discussed in Thread: BQ24130

Tool/software:

Hi expert, 

A question about the charger IC temperature protection. Currently we are working on the charger IC BQ24105. According to the data sheet, there is an equation to calculate the selection of RT1&RT2. But in some cases, for example the RTHcold is 25kΩ & RTHhot is 5kΩ, the result of RT1 would be -370kΩ but negative value is not applicable. I don’t know if there are any more conditions I need for the calculation, because in this way, some of the protection point cannot be applied. So I would like to know how I should select the RT1 and RT2 for the temperature protection function? 

Best regards,

Randy

  • 0
    TI__Guru**** 156721 points

    Hi Randy,

    Per the design example on datasheet page 27, a 10k ohm 103AT thermistor should work.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Intellectual 1920 points

    Hi Jeff,

    Thanks for the sharing, may I know whether TI has test waveform to show this function? We have put 10K NTC to detect temperature, but seems like it is not work at a range, I mean base on calculation charger should protect at 35~30 degree C.

    But it didn’t, we would like to know whether there has any configuration setting or some of HW solution to disable this function also?

    Best regards,

    Randy

  • 0 in reply to Randy Chen
    TI__Guru**** 156721 points

    HI Randy,

    Unfortunately, I do not have test waveform for this older device.  The link below is the to the BQ2413x/7x design calculator.  I copied a section from the BQ24130 tab for TS resistor calc and get the datasheet example values. I only changed the VTCO to match the VTHF % from the BQ24105 spec table.

    If the equations/calculator give a negative value, then that thermistor (or at R_COLD or R_HOT) is not compatible with the charger's TS pin.

    https://www.ti.com/tool/download/SLUC244

    To disable TS function, install equal sized resistors between VTSB and TS and GND.

    Regards,

    Jeff