The LTC®3305 is a lead-acid battery balancer that uses an auxiliary battery or an alternative storage cell (AUX) to transfer charge to and from individual batteries within a series-connected stack. The balancer controls external NMOS switches to sequentially connect the auxiliary battery to each battery in the stack. To prevent damage to the NMOS switches and their interconnecting PCB traces, a current limiting device is required. One such device is a ceramic positive temperature coefficient (PTC) thermistor.
Linear Technology, LTC3305,