SPVA059 June   2026 BQ21080 , BQ21088 , BQ24070 , BQ24071 , BQ24072 , BQ24073 , BQ24074 , BQ24075 , BQ24076 , BQ24078 , BQ24079 , BQ25150 , BQ25155 , BQ25157 , BQ25170 , BQ25170J , BQ25171-Q1 , BQ25172 , BQ25173 , BQ25173-Q1 , BQ25175 , BQ25176J , BQ25176K , BQ25176M , BQ25180 , BQ25185 , BQ25186 , BQ25188 , BQ25190

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Design Procedure
    1. 2.1 Step-by-Step Calculation Method
  6. 3Design Examples
    1. 3.1 Example 1: BQ25190 with Standard NTC Beta Value, 10°C to 45°C
    2. 3.2 Example 2: BQ25188 with Different NTC Beta Value, 0°C to 45°C
    3. 3.3 Example 3: BQ25170 with Standard NTC Beta Value, -10°C to 60°C
  7. 4Error Analysis
    1. 4.1 Worst-Case Analysis Method
    2. 4.2 Example: Worst-Case Error Analysis for BQ25190, 10°C to 45°C
  8. 5NTC Thermistor Modeling
  9. 6Summary
  10. 7References

3.2 Example 2: BQ25188 with Different NTC Beta Value, 0°C to 45°C

Design the current-based TS network for the BQ25188 to support the following charging requirements for a wearables application:

Suspend charging when the battery NTC is above 45°C or below 0°C. Use a 10kΩ, β(25/85°C)=3610K NTC.

  1. Identify the required battery temperature thresholds.

    • THOT = 45°C

    • TCOLD = 0°C

  2. Find the TS voltage thresholds from the BQ25188 datasheet.

    The BQ25188 has configurable HOT and COLD voltage thresholds, so select the thresholds that most closely match the required temperature thresholds. HOT=45°C and COLD=0°C thresholds are available, but these correspond to a 10kΩ, β(25/85°C)=3435K NTC. Since a different NTC is being used, series and parallel resistors are needed.

    • VHOT = 0.1850V

    • VCOLD = 1.0075V

  3. Determine the resistance of the NTC at THOT and TCOLD.

    Using the given 10kΩ at 25°C NTC with β(25/85°C)=3610K, the exponential form of the beta equation in Equation 1 is used to calculate RHOT and RCOLD:

    • RHOT = 4,671Ω

    • RCOLD = 30,288Ω

  4. Calculate the required series and parallel resistors.

    From the BQ25188 datasheet:

    • IBIAS = 38µA

    • VHOT = 0.1850V

    • VCOLD = 1.0075V

    Calculating the series resistor using Equation 2:

    • RS,1 = 320Ω

    • RS,2 = -35,279Ω

    Calculating the parallel resistor, RP, using the valid solution, RS,1, and Equation 3:

    • RP = 198,178Ω

    Selecting standard E96 series (1% tolerance) resistor values from the calculated values:

    • RS = 316Ω

    • RP = 196kΩ

  5. Verifying the TS thresholds that result from these resistor values using Equation 4:

    • VTS, HOT = 38µA (196kΩ || (316Ω + 4,671Ω)) = 0.1848V

    • VTS, COLD = 38µA ( 196kΩ || (316Ω + 30,288Ω)) = 1.0059V

    These thresholds align with the COLD and HOT thresholds of the BQ25188 listed in step 2.