Figure 9-4 VBUS Snubber

Another method of clamping the USB Type-C VBUS is to use a VBUS RC Snubber. An RC Snubber is a great solution because in general it is much smaller than a TVS diode, and typically more cost effective as well. An RC Snubber works by modifying the characteristic of the total RLC response in the USB Type-C cable hot-plug from being under-damped to critically-damped or over-damped. So rather than clamping the over-voltage directly, it actually changes the hot-plug response from under-damped to critically-damped, so the voltage on VBUS does not ring at all; so the voltage is limited, but without requiring a clamping element like a TVS diode.

However, the USB Type-C and Power Delivery specifications limit the range of capacitance that can be used on VBUS for the RC snubber. VBUS capacitance must have a minimum 1 µF and a maximum of 10 µF. The RC snubber values chosen support up to 4 m USB Type-C cable (maximum length allowed in the USB Type-C specification) being hot plugged, is to use 4.7-μF capacitor in series with a 3.48-Ω resistor. In parallel with the RC Snubber a 1 μF capacitor is used, which always ensures the minimum USB Type-C VBUS capacitance specification is met. This circuit can be seen in Figure 9-4.