The LP2985-N was designed to work with ceramic capacitors on the output to take advantage of the benefits these capacitors offer. For capacitance values in the 2.2-µF to 4.7-µF range, ceramics are the least expensive and also have the lowest ESR values (which makes these components the most efficient at eliminating high-frequency noise). The ESR of a typical 2.2-µF ceramic capacitor is in the range of 10 mΩ to 20 mΩ, which easily meets the ESR limits required for stability by the LP2985-N.

One disadvantage of ceramic capacitors is that the capacitance can vary with temperature. Most large-value ceramic capacitors (≥ 2.2 µF) are manufactured with the Z5U or Y5V temperature characteristic, which results in the capacitance dropping by more than 50% as the temperature goes from 25°C to 85°C.

This capacitance drop can cause problems if a 2.2-µF capacitor is used on the output because that capacitor can down to approximately 1 µF at high ambient temperatures (which can cause the LM2985 to oscillate). If Z5U or Y5V capacitors are used on the output, a minimum capacitance value of 2.2 µF must be observed.

A better choice for temperature coefficient in ceramic capacitors is X7R, which holds the capacitance within ±15%. Unfortunately, the larger values of capacitance are not offered by all manufacturers in the X7R dielectric.

Tantalum capacitors are less desirable than ceramics for use as output capacitors because they are more expensive when comparing equivalent capacitance and voltage ratings in the 1-µF to 4.7-µF range.

Another important consideration is that tantalum capacitors have higher ESR values than equivalent size ceramics. Which means that although a tantalum capacitor can possibly have an ESR value within the stable range, the capacitor must be larger in capacitance (which means bigger and more costly) than a ceramic capacitor with the same ESR value.

The ESR of a typical tantalum increases by approximately 2:1 as the temperature goes from 25°C down to –40°C, so some guard band must be allowed.