The ESR of a good-quality tantalum capacitor is almost directly centered in the middle of the stable range of the ESR curve (approximately 0.5 Ω–1 Ω). The temperature stability of tantalum capacitors is typically very good, with a total variation of only approximately 2:1 over the temperature range of –40°C to +125°C (ESR increases at colder temperatures). Avoid off-brand capacitors because some poor-quality tantalum capacitors are available with ESR values greater than 10 Ω, which usually causes oscillation problems. One caution regarding tantalum capacitors is that if used on the input, the ESR is low enough to be destroyed by a surge current if the capacitor is powered up from a low impedance source (such as a battery) that has no limit on inrush current. In this case, use a ceramic input capacitor that does not have this problem.

Ceramic capacitors are generally larger and more costly than tantalum capacitors for a given amount of capacitance. These capacitors also have a very low ESR that is quite stable with temperature. However, the ESR of a ceramic capacitor is typically low enough to make an LDO oscillate. A 2.2-μF ceramic demonstrated an ESR of approximately 15 mΩ when tested. If used as an output capacitor, this ESR can cause instability (see the ESR curves in the Typical Characteristics section). If a ceramic capacitor is used on the output of an LDO, place a small resistor (approximately 1 Ω) in series with the capacitor. If used as an input capacitor, no resistor is needed because there is no requirement for ESR on capacitors used on the input.