LP3910 datasheet(63/72 Pages) TI1

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LP3910

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SNVS481M – NOVEMBER 2006 – REVISED DECEMBER 2015

9.2.2.1.2

Method 2

A more conservative and recommended approach is to choose an inductor that has saturation current rating

greater than the maximum current limit.

INDUCTOR

VALUE

DESCRIPTION

NOTES

LSW1,2

2.2 µH

Buck1,2 Inductor

DCR 70 m

Ω

LBB

2.2 µH

Buck-Boost Inductor

DCR 70 m

Ω

9.2.2.2 External Capacitors

The regulators on the LP3910 require external capacitors for regulator stability. These are specifically designed

for portable applications requiring minimum board space and smallest components. These capacitors must be

correctly selected for good performance.

9.2.2.2.1

LDO Capacitor Selection

9.2.2.2.1.1

Input Capacitor

An input capacitor is required for stability. It is recommended that a 1-µF capacitor be connected between the

LDO input pin and ground. (This capacitance value may be increased without limit.)

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

Tantalum capacitors can suffer catastrophic failures due to surge currents 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 should be ensured 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

approximately 1 µF over the entire operating temperature range.

9.2.2.2.1.2

Output Capacitor

The LDOs on the LP3910 are designed specifically to work with very small ceramic output capacitors. A 1-

μF

ceramic capacitor (temperature types Z5U, Y5V or X7R) with ESR between 5 m

Ω to 500 mΩ, are suitable in the

application circuit.

Tantalum or film capacitors may also be used at the device output, COUT (or VOUT), but these are not as attractive

for reasons of size and cost.

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

value that is within the range 5 m

Ω to 500 mΩ for stability.

9.2.2.2.1.3

Capacitor Characteristics

The LDOs are designed to work with ceramic capacitors on the output to take advantage of the benefits they

offer. For capacitance values in the range of 0.47 µF to 4.7 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 LDOs.

For both input and output capacitors, careful interpretation of the capacitor specification is required to ensure

correct device operation. The capacitor value can change greatly, depending on the operating conditions and

capacitor type.

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