8.3.7.4.1 JEITA Guideline Compliance in Charge Mode

To improve the safety of charging Li-ion batteries, JEITA guideline was released on April 20, 2007. The guideline emphasized the importance of avoiding a high charge current and high charge voltage at certain low and high temperature ranges.

To initiate a charge cycle, the voltage on TS pin must be within the VT1 to VT5 thresholds. If TS voltage exceeds the T1-T5 range, the controller suspends charging and waits until the battery temperature is within the T1 to T5 range. At cool temperature (T1-T2), JEITA recommends the charge current to be reduced to half of the charge current or lower. At warm temperature (T3-T5), JEITA recommends charge voltage less than 4.1 V / cell.

On the BQ25886, at cool temperature (T1-T2), the charge current is reduced to 20% of the fast charge current, ICHG. At warm temperature (T3 - T5), the charge voltage is set to 8.0 V. Whenever the charger detectes "warm" or "cool" temperature, termination is automatically disabled.

Figure 18. TS Resistor Network

Assuming a 103AT NTC (Negative Temperature Coefficient) thermistor on the battery pack as shown above, the value of RT1 and RT2 can be determined by:

Equation 1.

Equation 2.

Select 0°C to 60°C range for Li-ion or Li-polymer battery:

R_NTC,T1 = 27.28 kΩ

R_NTC,T5 = 3.02 kΩ

RT1 = 5.24 kΩ

RT2 = 30.31 kΩ