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BQ51050B NTC Circuit

Tom Saluzzo
Expert 1280 points

On page 22 of the TI BQ51050 datasheet, they suggest adding two additional resistors R1 and R3 to the NTC. Using the suggested Panasonic NTC (ERT-JZEG103JA) without the added resistors, I get results that agree with the thresholds on page 5 and Figure 26. Adding the resistors just desensitizes the NTC. I don’t see the need for R1 and R3. What am I missing?

Also I don’t see anything in the datasheet that describes what happens at each threshold.

  • 0
    TI__Genius 14890 points

    Tom,

    You are not missing anything.  The schematic and equation allow for other NTC resistors to be used.  If you are getting the values expected, then your system will work properly.

    Please see the section on page 21 titled "Battery-Charger Safety and JEITA Guidelines".  Figure 22 on page 20 illustrates the thresholds.  It shows the JEITA compatible TS Profile.  At temperatures from 0C to 10C, the maximum charge is 0.5C.  Between 10C and 45C, the maximum charge is 1C.  Above 45C, the current backs off to 0.5C and the maximum voltage changes as well.

    Regards,

    Dick