3 RC Snubber

Figure 2-2 shows that minimizing the input stray inductance, increasing the input capacitance, and adding resistance (including using higher ESR capacitors) helps suppress the input voltage spike. However, a user often cannot control input stray inductance and adding additional large capacitance increases cost and takes up more board space.

The damping factor is

Cable lengths for electronic devices, and therefore the series inductance Li, vary significantly. The power pin capacitance varies by IC as well and, in general, cannot have a large series resistance. Therefore, the most efficient and cost-effective approach is to not use the IC pin's capacitance but add an additional small capacitor and series resistor as a snubbing filter or, more commonly called, RC snubber.

Figure 3-1 depicts the recommended input filter design for the BQ2579x family. The filter can be placed on the PCB at the device connector or closer to the IC if long PCB traces and GND returns are used.

This RC combination is effective for most commonly used adapter cable lengths, but the RC combination can require adjusting for some applications (bq24753A Host-Controlled Li-Ion and Li-Polymer Battery Charger With Low Iq and System Power Selector.