Application Hints

OUTPUT CAPACITOR

Like any low-dropout regulator, the LP2980 requires an out-

put capacitor to maintain regulator loop stability. This capaci-

tor must be selected to meet the requirements of minimum

capacitance and equivalent series resistance (ESR) range. It

is not difficult to find capacitors which meet the criteria of the

LP2980, as the acceptable capacitance and ESR ranges are

wider than for most other LDOs.

In general, the capacitor value must be at least 1 µF (over

the actual ambient operating temperature), and the ESR

must be within the range indicated in

Figures 1, 2 and Figure

3. It should be noted that, although a maximum ESR is

shown in these Figures, it is very unlikely to find a capacitor

with ESR that high.

Tantalum Capacitors

Surface-mountable solid tantalum capacitors offer a good

combination of small physical size for the capacitance value,

and ESR in the range needed by the LP2980.

The

results

of

testing

the

LP2980

stability

with

surface-mount solid tantalum capacitors show good stability

with values of at least 1 µF. The value can be increased to

2.2 µF (or more) for even better performance, including tran-

sient response and noise.

Small value tantalum capacitors that have been verified as

suitable for use with the LP2980 are shown in

Table 2. Ca-

pacitance values can be increased without limit.

Aluminum Electrolytic Capacitors

Although probably not a good choice for a production design,

because of relatively large physical size, an aluminum elec-

trolytic capacitor can be used in the design prototype for an

LP2980 regulator. A value of at least 1 µF should be used,

and the ESR must meet the conditions of

Figures 1, 2 and

Figure 3. If the operating temperature drops below 0˚C, the

regulator may not remain stable, as the ESR of the alumi-

num electrolytic capacitor will increase, and may exceed the

limits indicated in the Figures.

TABLE 2. Surface-Mount Tantalum Capacitor

Selection Guide

1 µF Surface-Mount Tantalums

Manufacturer

Part Number

Kemet

T491A105M010AS

NEC

NRU105M10

Siemens

B45196-E3105-K

Nichicon

F931C105MA

Sprague

293D105X0016A2T

2.2 µF Surface-Mount Tantalums

Manufacturer

Part Number

Kemet

T491A225M010AS

NEC

NRU225M06

Siemens

B45196/2.2/10/10

Nichicon

F930J225MA

Sprague

293D225X0010A2T

Multilayer Ceramic Capacitors

Surface-mountable multilayer ceramic capacitors may be an

attractive choice because of their relatively small physical

size and excellent RF characteristics. However, they some-

times have ESR values lower than the minimum required by

the LP2980, and relatively large capacitance change with

temperature. The manufacturer’s datasheet for the capacitor

should be consulted before selecting a value.

Test results of LP2980 stability using multilayer ceramic ca-

pacitors show that a minimum value of 2.2 µF is usually

needed for the 5V regulator. For the lower output voltages, or

for better performance, a higher value should be used, such

as 4.7 µF.

Multilayer ceramic capacitors that have been verified as suit-

able for use with the LP2980 are shown in

Table 3.

TABLE 3. Surface-Mount Multilayer Ceramic Capacitor

Selection Guide

2.2 µF Surface-Mount Ceramic

Manufacturer

Part Number

Tokin

1E225ZY5U-C203

Murata

GRM42-6Y5V225Z16

4.7 µF Surface-Mount Ceramic

Manufacturer

Part Number

Tokin

1E475ZY5U-C304

DS012078-48

FIGURE 1. 1 µF ESR Range

DS012078-49

FIGURE 2. 2.2 µF ESR Range

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