LP3992

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SNVS192C – OCTOBER 2002 – REVISED NOVEMBER 2015

9.2.2.2 Input Capacitor

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

LP3992 IN pin and ground (this capacitance value may be increased without limit).

This capacitor must be located a distance of not more than 1 cm from the IN 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 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 equivalent series resistance (ESR) on the input capacitor, but tolerance and

temperature coefficient must be considered when selecting the capacitor to ensure the capacitance will remain

≊

1 µF over the entire operating temperature range.

9.2.2.3 Output Capacitor

The LP3992 is designed specifically to work with very small ceramic output capacitors. A 1-µF ceramic capacitor

(dielectric types Z5U, Y5V or X7R) with ESR from 5 m

Ω to 500 mΩ, is suitable in the LP3992 application circuit.

For this device the output capacitor should be connected between the CAP pin and ground. It is also possible to

connect the output capacitor directly to the OUT pin. In this case the CAP pin must be left open-circuit or tied

directly to the OUT pin.

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

for reasons of size and cost (see Capacitor Characteristics).

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

value that is within the 5-m

Ω to 500-mΩ range for stability.

Table 2. Recommended Output Capacitor

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

Capacitance(1)

0.7

1

µF

COUT

Output capacitor

ESR

5

500

m

Ω

(1)

The capacitor tolerance should be ±30% or better over the temperature range. The recommended capacitor type is X7R however,

dependant on the application X5R, Y5V, and Z5U can also be used.

9.2.2.4 No-Load Stability

The LP3992 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.

9.2.2.5 Capacitor Characteristics

The LP3992 is designed to work with ceramic capacitors on the output to take advantage of the benefits they

offer. For capacitance values in the 1-µF to 4.7-µF range, 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 20-m

Ω to 40-mΩ range that easily meets the ESR requirement for

stability for the LP3992.

The temperature performance of ceramic capacitors varies by type. Most large-value ceramic capacitors

(

≥ 2.2 µF) are manufactured with Z5U or Y5V temperature characteristics, which results in the capacitance

dropping by more than 50% as the temperature goes from 25°C to 85°C.

A better 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 4.7-µF range.

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