9.2.2.4 Additional ESD Protection on CC and SBU Lines

If additional IEC ESD protection is desired to be placed on either the CC or SBU lines, it is important that high-voltage ESD protection diodes be used. The maximum DC voltage that can be seen in USB PD is 21-V_BUS, with 21.5 V allowed during voltage transitions. Therefore, an ESD protection diode must have a reverse stand off voltage higher than 21.5 V in order to guarantee the diode does not breakdown during a short-to-V_BUS event and have large amounts of current flowing through it indefinitely, destroying the diode. A reverse stand off voltage of 24 V is recommended to give margin above 21.5 V in case USB Type-C power adaptors are released in the market which break the USB Type-C specification.

Furthermore, due to the fact that the Short-to-V_BUS event applies a DC voltage to the CC and SBU pins, a deep-snap-back diode cannot be used unless its minimum trigger voltage is above 42 V. During a Short-to-V_BUS event, RLC ringing of up to 2x the settling voltage can be exposed to CC and SBU, allowing for up to 42 V to be exposed. Furthermore, if any capacitor derates on the CC or SBU line, greater than 2x ringing can occur. Since this ringing is hard to bound, it is recommended to not use deep-snap-back diodes. If the deep-snap-back diode triggers during the short-to-V_BUS hot-plug event, it begins to operate in its conduction region. With a 20-V_BUS source present on the CC or SBU line, this allows the diode to conduct indefinitely, destroying the diode.