Vishay’s application note on fast charging control using NTC and TI’s BQ2005. Link here (PDF)
The need for increased autonomy for new models of laptops and cellular phones has resulted in high-energy density power packs – Ni MH and Li-ion batteries. These batteries can be charged quickly, on the condition that the fast charging complies with several criteria.
The sophistication of the electronic system depends principally upon cost and upon the requirements of the batteries. Often, the fast charging is monitored by an IC, measuring the voltage of the batteries, the char-ging current via a sense resistor, and measuring the temperature of the batteries via one or several Negative Temperature Coefficient (NTC) thermistor(s). The IC’s are almost always in the chargers or integrated in the battery pack (Li-ion). The thermistors are almost always integrated in the battery packs, sometimes placed in the charger, and/or in the final apertures (low cost cellular phones).
This application note explains how to design an NTC thermistor from Vishay BCcomponents for a BQ2005 from TEXAS INSTRUMENTS dual Ni MH batteries charging IC.