To improve the safety of charging Li-ion batteries, the 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, as a percentage of V_REGN, must be within the V_{T1_FALL%} to V_{T5_RISE%} thresholds. If the TS voltage percentage exceeds the T1-T5 range, the controller suspends charging, a TS fault is reported and waits until the battery temperature is within the T1-T5 range.

At cool temperature (T1-T2), the charge current is reduced to a programmable fast charge current (0%, 20% default, 50%, 100% of I_CHG, by JEITA_ISET). At warm temperature (T3-T5), the charge voltage is reduced to 4.1 V or kept at V_REG (JEITA_VSET), and the charge current can be reduced to a programmable level (0%, 20%, 50%, 100% default). Battery termination is disabled in T3-T5. The charger provides more flexible settings on a T2 and T3 threshold as well to program the temperature profile beyond JEITA. When T1 is set to 0°C and T5 is set to 60°C, T2 can be programmed to 5.5°C/10°C (default)/15°C/20°C, and T3 can be programmed to 40°C/45.5°C (default)/50.5°C/54.5°C.

When the charger does not need to monitor the NTC, the host sets the TS_IGNORE bit to 1 to ignore the TS pin condition during charging and Boost mode. If the TS_IGNORE bit is set to 1, the TS pin is ignored and the charger ignores the TS pin input. In this case, the NTC_FAULT bits are 000 to report normal TS status.

Figure 8-4 JEITA Profile

Equation 1 through Equation 2 describe how to calculate resistor divider values on the TS pin.

Figure 8-5 TS Pin Resistor Network

Equation 1.

Equation 2.

In the equations above, R_{NTC, T1} is the NTC thermistor resistance value at temperature T1 and R_{NTC, T5} is the NTC thermistor resistance value at temperature T5. Selecting a 0°C to 60°C range for a Li-ion or Li-polymer battery then:

• R_NTC,T1 = 27.28 kΩ (0°C)
• R_NTC,T5 = 3.02 kΩ (60°C)
• RT1 = 5.3 kΩ
• RT2 = 31.14 kΩ