The Temperature Sensing (TS) function is a vital function for providing batteries charge and to operate within a safe temperature range. The BQ25180 provides a TS design as a current source that biases a resistor network with an NTC thermistor. Although the TS is designed to work with NTC of particular characteristics, external resistors extend the NTCs which can be used with the BQ25180. The External NTC Monitoring Calculator, which is available on the TI-Charger GUI, provides an easy means to check the configured application's expected TS behavior.
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Temperature sensing of the battery is a precautionary measure to maintain the battery within safe temperatures during the course of charging. Temperature sensing feature makes use of temperature sensitive resistivity to approximate and respond to battery temperatures while charging. For this purpose, many battery manufacturers incorporate a Negative Temperature Coefficient thermistor into the battery pack; for those battery packs that do not have a thermistor, we recommend including an external NTC alongside the battery pack.
The Japanese Electronics and Information Technology Industries Association (JEITA) guidelines for improving battery charging safety outline a series of battery temperature thresholds which can affect the charging parameters when crossed. These thresholds are typically defined as: cold temperatures below 0°C, cool temperatures below 10°C but above 0°C, warm temperatures above 45°C but below 60°C, and hot temperatures above 60°C. The prescribed behavior for the temperatures below the cold threshold and above the hot threshold is to cease charging until battery temperature has normalized. For battery temperatures in the cool and warm regions charge current and maximum charge voltage can be reduced. Different guidelines apply to different applications, we recommend checking the specific guidelines that apply to a given battery pack.