The BQ2409x family contains an NTC monitoring function. The TS function for BQ24090, BQ24091, and BQ24095 follows the classic temperature range and disable charge when the battery temperature is outside of the 0°C and 45°C operating temperature window. The TS function for BQ24092 and BQ24093 is designed to follow the new JEITA temperature standard for Li-ion and Li-pol batteries. There are now four thresholds, 60°C, 45°C, 10°C, and 0°C. Normal operation occurs between 10°C and 45°C. If between 0°C and 10°C the charge current level is cut in half, and if between 45°C and 60°C the regulation voltage is reduced to 4.1 V max, see Figure 9-4.

The BQ2409x family has devices to monitor 10-k and 100-k NTC thermistors. The BQ24090/2/5 are designed to work with a 10-k NTC. For these devices, the TS feature is implemented using an internal 50-μA current source to bias the thermistor (designed for use with a 10-k NTC β = 3370 (SEMITEC 103AT-2 or Mitsubishi TH05-3H103F) connected from the TS pin to V_SS. If this feature is not needed, a fixed 10-k can be placed between TS and V_SS to allow normal operation. This may be done if the host is monitoring the thermistor and then the host would determine when to pull the TS pin low to disable charge. The BQ24091/3 are designed to work with a 100-k NTC. For these devices, the TS feature is implemented using an internal 5-μA current source to bias the thermistor (designed for use with a 100-k NTC β = 3370) connected from the TS pin to V_SS. If this feature is not needed, a fixed 100-k can be placed between TS and V_SS to allow normal operation. This may be done if the host is monitoring the thermistor and then the host would determine when to pull the TS pin low to disable charge.

The TS pin has two additional features when the TS pin is pulled low or floated/driven high. A low disables charge (similar to a high on the BAT_EN feature) and a high puts the charger in TTDM.

Above 60°C or below 0°C the charge is disabled. Once the thermistor reaches ≈–10°C the TS current folds back to keep a cold thermistor (between –10°C and –50°C) from placing the IC in the TTDM Mode. If the TS pin is pulled low into Disable Mode, the current is reduced to ≈30 μA, see Figure 9-2. Since the I_TS current is fixed along with the temperature thresholds, it is not possible to use thermistor values other than the 10-k or 100-k (depending on the IC) NTC (at 25°C).