ESR and LI of a Capacitor
Every capacitor includes a parasitic series inductance, called the lead inductance (LI). LI is also referred to as package or mounting inductance, or sometimes as effective series inductance (ESL).
Every capacitor also includes a parasitic series resistance, called the equivalent series resistance (ESR). It acts to defeat the effectiveness of a capacitor. ESR is a real-valued impedance and is not a strong function of frequency. ESR acts like a resistor in series with a capacitor. Lead inductance acts like an inductor in series with the same capacitor.
The equation for capacitor impedance as a function of frequency is given by:
where: