Calibrating the Current Offset Bias (COB) Register for the DS278x Family of Fuel Gauges

Abstract: The DS278x family of stand-alone fuel gauges provides an accurate estimation of the remaining capacity available in rechargeable lithium-ion or lithium-polymer batteries. These fuel gauges contain a current offset bias (COB) register that can be utilized by the designer to eliminate the inherent offset introduced by the IC's current ADC. Improper calibration of this register, however, can decrease the accuracy of the current measurements, especially at low currents. This application note describes a step-by-step approach for properly calibrating the DS278x within the fully assembled battery pack in order to determine the correct value that should be placed into the COB register.