LP8900

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SNVS542C – MAY 2008 – REVISED JULY 2013

APPLICATION INFORMATION

External Capacitors

In common with most regulators, the LP8900 requires external capacitors for regulator stability. The LP8900 is

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

capacitors must be correctly selected for good performance.

Input Capacitor

An input capacitor is required for stability. It is recommended that a 1.0 µF capacitor be connected between the

LP8900 input pin and ground (this capacitance value may be increased to 10 µF).

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

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

Important: Tantalum capacitors can suffer catastrophic failures due to surge current when connected to a low-

impedance source of power (like a battery or a very large capacitor). If a tantalum capacitor is used at the input,

it must be ensured by the manufacturer to have a surge current rating sufficient for the application.

There are no requirements for the ESR (Equivalent Series Resistance) on the input capacitor, but tolerance,

temperature, and voltage coefficients must be considered when selecting the capacitor to ensure the capacitance

will remain

≊ 1.0µF over the entire operating temperature range.

Output Capacitor

Correct selection of the output capacitor is critical to ensure stable operation in the intended application.

The output capacitor must meet all the requirements specified in the recommended capacitor table over all

conditions in the application. These conditions include DC bias, frequency and temperature. Unstable operation

will result if the capacitance drops below the minimum specified value.

The LP8900 is designed specifically to work with very small ceramic output capacitors. A 1.0µF ceramic

capacitor (dielectric type X7R or X5R) with an ESR between 5m

Ω to 500mΩ, is suitable in the LP8900

application circuit.

Other ceramic types such as Y5V and Z5U are less suitable owing to their inferior temperature characteristics.

(See section on Capacitor Characteristics).

It is also recommended that the output capacitor is placed within 1cm of the output pin and returned to a clean,

low impedance, ground connection.

reasons of size and cost (see the section Capacitor Characteristics).

No-Load Stability

The LP8900 will remain stable and in regulation with no external load. This is an important consideration in some

circuits, for example CMOS RAM keep-alive applications.

Capacitor Characteristics

The LP8900 is designed to work with ceramic capacitors on the input and outputs to take advantage of the

benefits they offer. For capacitance values around 1.0 µF, ceramic capacitors give the circuit designer the best

design options in terms of low cost and minimal area.

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 dependant on the conditions of operation and

capacitor type.

In particular, to ensure stability, the output capacitor selection should take account of all the capacitor

parameters, to ensure that the specification is met within the application. Capacitance value can vary with DC

bias conditions as well as temperature and frequency of operation. Capacitor values will also show some

decrease over time due to aging. The capacitor parameters are also dependant on the particular case size with

smaller sizes giving poorer performance figures in general.

Copyright © 2008–2013, Texas Instruments Incorporated

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