LP2980
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
Kemet
NEC
Siemens
Nichicon
Sprague
Manufacturer
Kemet
NEC
Siemens
Nichicon
Sprague
Part Number
T491A105M010AS
NRU105M10
B45196-E3105-K
F931C105MA
293D105X0016A2T
2.2 µF Surface-Mount Tantalums
Part Number
T491A225M010AS
NRU225M06
B45196/2.2/10/10
F930J225MA
293D225X0010A2T
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
Tokin
Murata
Manufacturer
Tokin
Part Number
1E225ZY5U-C203
GRM42-6Y5V225Z16
4.7 µF Surface-Mount Ceramic
Part Number
1E475ZY5U-C304
DS012078-48
FIGURE 1. 1 µF ESR Range
DS012078-49
FIGURE 2. 2.2 µF ESR Range
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-
www.national.com
12
NSC [ NATIONAL SEMICONDUCTOR ]
