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LP5912

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SNVSA77B – DECEMBER 2015 – REVISED JUNE 2016

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9.2.2 Detailed Design Procedure

9.2.2.1 External Capacitors

Like most low-dropout regulators, the LP5912 requires external capacitors for regulator stability. The device is

specifically designed for portable applications requiring minimum board space and smallest components. These

capacitors must be correctly selected for good performance.

9.2.2.2 Input Capacitor

An input capacitor is required for stability. The input capacitor must be at least equal to, or greater than, the

output capacitor for good load-transient performance. A capacitor of at least 1 µF must be connected between

the LP5912 IN pin and ground for stable operation over full load-current range. It is acceptable to have more

output capacitance than input, as long as the input is at least 1 µF.

The input capacitor must be located a distance of not more than 1 cm from the input pin and returned to a clean

analog ground. Any good-quality ceramic, tantalum, or film capacitor may be used at the input.

NOTE

To ensure stable operation it is essential that good PCB practices are employed to

minimize ground impedance and keep input inductance low. If these conditions cannot be

met, or if long leads are to be used to connect the battery or other power source to the

LP5912, increasing the value of the input capacitor to at least 10 µF is recommended.

Also, tantalum capacitors can suffer catastrophic failures due to surge current when

connected to a low-impedance source of power (such as a battery or a very large

capacitor). If a tantalum capacitor is used at the input, it must be verified by the

manufacturer to have a surge current rating sufficient for the application. There are no

requirements for the equivalent series resistance (ESR) on the input capacitor, but

tolerance and temperature coefficient must be considered when selecting the capacitor to

ensure the capacitance remains 1

μF ±30% over the entire operating temperature range.

9.2.2.3 Output Capacitor

The LP5912 is designed specifically to work with a very small ceramic output capacitor, typically 1 µF. A ceramic

capacitor (dielectric types X5R or X7R) in the 1-µF to 10-µF range, and with an ESR from 5 m

Ω to 500 mΩ, is

suitable in the LP5912 application circuit. For this device the output capacitor must be connected between the

OUT pin with a good connection back to the GND pin.

reasons of size and cost (see Capacitor Characteristics).

The output capacitor must meet the requirement for the minimum value of capacitance and have an ESR value

that is within the range 5 m

Ω to 500 mΩ for stability.

9.2.2.4 Capacitor Characteristics

The LP5912 is designed to work with ceramic capacitors on the input and output to take advantage of the

benefits they offer. For capacitance values in the range of 1 µF to 10 µF, ceramic capacitors are the smallest,

least expensive, and have the lowest ESR values, thus making them best for eliminating high frequency noise.

The ESR of a typical 1-µF ceramic capacitor is in the range of 20 m

Ω to 40 mΩ, which easily meets the ESR

requirement for stability for the LP5912.

The preferred choice for temperature coefficient in a ceramic capacitor is X7R. This type of capacitor is the most

stable and holds the capacitance within ±15% over the temperature range. Tantalum capacitors are less

desirable than ceramic for use as output capacitors because they are more expensive when comparing

equivalent capacitance and voltage ratings in the 1-µF to 10-µF range.

Another important consideration is that tantalum capacitors have higher ESR values than equivalent size

ceramics. While it may be possible to find a tantalum capacitor with an ESR value within the stable range, it

would have to be larger in capacitance (which means bigger and more costly) than a ceramic capacitor with the

same ESR value. Also, the ESR of a typical tantalum increases about 2:1 as the temperature goes from 25°C

down to –40°C, so some guard band must be allowed.