Towards single-event transients (SETs) in charge pumps (CPs) for phase-locked loops (PLLs), the effects brought about by different frequency SETs induced currents are analyzed. Based on frequency domain analyses, the relation between loop parameters and SET response is investigated with respect to gain and bandwidth. The results reveal that decreasing the loop filter resistance to decrease the gain can significantly mitigate the SET induced voltage perturbation of the voltage-controlled oscillator's (VCO) control voltage, and that increasing the damping ratio or the nature frequency to increase the bandwidth can filter out more SET currents in a wider frequency range and effectively reduce the PLL recovery time. Therefore, decreasing the loop filter resistance, increasing the damping ratio or the nature frequency are effective radiation-hardened-by-design techniques. Eventually, the conclusions are validated by transistor-level simulations for a 1GHz PLL.