LP3995

SNVS179F – FEBRUARY 2003 – REVISED SEPTEMBER 2015

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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 remains

≅ 1

µF over the entire operating temperature range.

9.2.2.3 Output Capacitor

The LP3995 is designed specifically to work with very small ceramic output capacitors. A ceramic capacitor

(dielectric types Z5U, Y5V or X7R) in the 1-µF to 10-µF range, and with ESR between 5 m

Ω to 500 mΩ, is

suitable in the LP3995 application circuit.

For this device the output capacitor should be connected between the OUT pin and ground.

It may also be possible to use tantalum or film capacitors at the device output, VOUT, 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 range 5 m

Ω to 500 mΩ for stability.

Table 2. Recommended Output Capacitor

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

Units

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 LP3995 remains 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 LP3995 is designed to work with ceramic capacitors on the output to take advantage of the benefits they

offer. For capacitance values in the range of 1 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 LP3995.

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.

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

ceramics. This means that 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. It should also be noted that 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.

14

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