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BQ21040: NTC beta modification

Marco Hsieh
Intellectual 1060 points

Part Number: BQ21040

Hi experts,

Datasheet describe that BQ21040 should use 10k NTC β=3370, but datasheet recommend SEMITEC and Mitsubishi part is β=3435.

  1. May I know which β I should follow?? 3370 or 3435?
  2. May we have RTS calculation formula if customer use different β?

Marco

  • 0
    TI__Mastermind 18235 points

    Hi Marco,

    I saw your E2E forum. and for your question, I think these two β should be fine for application.

    See below resistor comparison table based on temperature then you can find the difference is small.

     Temp

    B=3435

    B=3370

    0

    28.704k

    28.137k

    5

    22.897k

    22.54k

    10

    18.41k

    18.199k

    15

    14.915k

    14.803k

    20

    12.171k

    12.126k

    25

    10k

    10k

    30

    8.269k

    8.299k

    35

    6.88k

    6.929k

    40

    5.759k

    5.819k

    45

    4.847k

    4.914k

     

    As for calculation Tool, I don't have it. and will ask team for tool.

    But I quickly write bq21040 RHOT(5.5kohm) and RCOLD(25kohm) resistor value for your reference

     And below table is temperature mapping with NTC resistor .

    Hope it is something helpful for you.

    Thanks

     

    Temp

    B=3435

    B=3370

    2

    26.297k

    25.724k

    3

    25.04k

    24.607k

    41

    5.561k

    5.623k

    42

    5.371k

    5.435k

    Battery pack NTC monitor Typical
    INTC 50 uA
    VHOT 0.275 V
    VCOLD 1.250 V
    Predicted thermistor resistance range to satisfy VHOT and VCOLD thresholds:
    NTC nomal
    RHOT 5.50 kohms RHOT = VHOT/INTC
    RCOLD 25.00 kohms VCOLD = VCOLD/INTC

    Temp

    B=3435

    B=3370

    2

    26.297k

    25.724k

    3

    25.04k

    24.607k

    41

    5.561k

    5.623k

    42

    5.371k

    5.435k

  • 0
    TI__Prodigy 640 points

    Hello Marco,

    Paul has good info on the Beta values.

    As for RTS, is used to decide whether to put device in TTDM or not (see TTDM description, sec 8.4.6). It is not used to adjust for different thermistors.