Did You Know

60 Acceleration (g) 50

30 Improved SMD

A D 10 Vishay extended AEC-Q200 0 B 00.511.5 2.0 f (kHz) DID YOU KNOW? C CAPACITANCE AND ESR THE ART AND SCIENCE OF USING ALUMINUM ELECTROLYTIC CAPACITORS 60 Acceleration (g) 50 High vibration s Aluminum electrolytic capacitors are prized for their low cost and large capacitance in small case sizes, designers need 40 to keep in mind their ample parasitics when designing them into an application.

30 Unipolar Design ESL The figure on the left shows the equivalent electrical circuit of an aluminum electrolytic 20 capacitor. The capacitor itself consists of two capacitors in series: the main anode capacitor and the series cathode capacitor. The cathode capacitor should be connected to 10 Standard vibration s the negative pole, and allows for reverse bias up to 1 V. Above this value, oxidation of the AEC-Q200 ESR (f,T) 0 cathode foil will take place, creating internal gas pressure and an irreversible drop in total 00.511.5 2.0 2 1 capacitance. ESR + ωL- ωC 2 f (kHz)

CA(f) The anode is the positive terminal and allows for voltages up to the rated voltage. Above this voltage, the leakage current will start to rise quickly, 60ultimately giving rise to a short Acceleration circuit once the voltage rises above the breakdown voltage(g) of the electrolyte. The capacitor 50 is clearly a unipolar design. 40 CC(f) Ileak(t,T,U)

Equivalent Series Resistance (ESR) 30 Improved SMD Both capacitors consist of an aluminum sheet as an electrode, and an electrolyte as a 20 counter-electrode. This electrolyte is a liquid with salts which is contained in the paper

spacer present betweenA the 2D layers of aluminum foil. It is10 conductive but with a high Vishay extended resistivity. This is the base for the series resistance (ESR). This ESR is typically dominated AEC-Q200 0 by the aluminum oxide Bresistance in the low frequency zone00 (typically.511 up to 100 Hz) and.5 2.0 by the paper / electrolyte in the mid and high frequency area (> 1 kHz). f (kHz) C Equivalent Series Inductance (ESL) The two metal sheets forming the anode and cathode are nicely wound around each oth- 60 er in the winding of the electrolytic capacitor. As such,Acceleration the self-inductance of the winding (g) is negligible. But the two metal strips connecting the anode50 and cathode sheets with the High vibration s outside world cannot be shielded properly, and the length of these so-called tabs defines 40 the self-inductance (ESL) of the capacitor. Typically, values for the ESL are 5 nH to 25 nH and rise with the dimensions of the capacitor. 30 ESL 20

Impedance (Z) 10 Standard vibration s AEC-Q200 ESR (f,T) The sum of the capacitance, ESR, and ESL yields to the 0impedance (Z) of the capacitor. 00.511.5 2.0 2 1 The value is Z= ESR + ωL- ωC 2 f (kHz) C (f) with ω= 2π* f, the frequency of the ripple current passing through the capacitor branch. A

As a function of frequency, Z shows a bathtub kind of shape. Z drops with frequencies in the low frequency range (Z ~ 1/ωC); it is relatively flat in the mid range frequencies (Z ~ CC(f) Ileak(t,T,U) ESR); and Z increases with frequencies in the high frequency range (Z ~ ωL).