The number of required PTC elements can be calculated from the equation shown on this slide. For example, the B59109J0130A020 has a heat capacity of approximately 2.3 J/K and a reference temperature of 130˚C. The two components maybe connected in either parallel or series. Satisfaction of the above equation ensures that the PTC ceramic does not exceed the reference temperature up to completion of charging and thus remains in the low-resistance range.