So, what are ESD capacitors? ESD capacitors can be defined as a capacitor that is rated to a specified ESD value using standardized testing, such as AEC-Q200 or IEC 61000-4-2, and is design controlled throughout the lifetime of the part to maintain the ESD rating. There are two primary functions of an ESD rated capacitor. First, ESD rated capacitors can be used for general purpose applications such as filtering, bypassing, and timing. These capacitors are not used for protecting integrated circuits but may be mounted in locations that are susceptible to ESD. In this case, a designer may want to choose an ESD rated capacitor to ensure it can survive ESD pulses that it may see during the application. Second, ESD rated capacitors can be used to protect other circuits from ESD pulses. In this case, a designer must determine what capacitance value and voltage rating will produce effective ESD suppression for protecting downstream components. Just because an ESD capacitor has a high ESD rating, it does not mean it is good for protecting against ESD.