Input Filter Design for Portable Power Management System

In a portable battery charger system, the adapter hot plug-in may cause high-voltage spikes at the input due to the resonance of the input cable stray inductance and the input capacitance. Solutions with too many input capacitors are undesirable because this would increase cost. This application report presents the design of the input filter aiming at minimizing the input voltage spike, the cost, and the size. The key is to reduce the quality factor of the resonant circuit by introducing high-ESR capacitors or adding resistors. Measurement results substantiate the effectiveness of this approach. Application examples and discussions are offered.