capacitor). If a Tantalum input capacitor is used, it must be

guaranteed by the manufacturer to have a surge current

rating sufficient for the application.

There are no requirements for ESR on the input capacitor,

but tolerance and temperature coefficient must be consid-

ered when selecting the capacitor to ensure the capacitance

will be

≥ 1 µF over the entire operating range.

OUTPUT CAPACITOR

The LP2980 requires an output capacitor to maintain loop

stability. The capacitor must be selected to meet the require-

ments of capacitance and ESR (equivalent series resis-

tance) over the full operating temperature range of the ap-

plication (see SELECTING THE OUTPUT CAPACITOR).

The minimum amount of capacitance which can be used on

the output is 2.2 µF, but this value may be increased without

limit.

Four curves are provided which show the stable ESR range

of the LP2980-1.8V operated with output capacitances of

2.2, 4.7, 10, and 15 µF:

10109118

2.2 µF ESR Curves For 1.8V Output

10109119

4.7 µF ESR Curves For 1.8V Output

10109120

10 µF ESR Curves For 1.8V Output

10109121

15 µF ESR Curves For 1.8V Output

It should be noted that for the lower values of the output

tor and series resistance to provide sufficient ESR. To un-

derstand why this is true, the basic characteristics of capaci-

tance types must be explained:

CAPACITOR CHARACTERISTICS:

Ceramic Capacitors have an extremely low ESR (in the

range of 5-15 m

Ω), and can only be used on the output of the

LP2980 if an external resistor is placed in series to supply

the needed ESR (a resistance value of about 2

Ω +/− 30% is

recommended).

Be careful of the temperature coefficient of ceramics: select

X7R or X5R if possible, because those types typically vary

less than +/− 25% over the range of −40 to +125˚C. Z5U

types are worse, and will typically lose half (or more) of their

capacitance over the same temperature range.

A source for large-value ceramics with good performance is

Taiyo-Yuden. Their web address is :

http://www.t-yuden.com/hicap.html

Tantalum capacitors have ESR values that are more diffi-

cult to determine: the manufacturers specify only a maxi-

mum limit, which is typically 10X or 20X the typical value.

ESR values can vary considerably from lot to lot and from

manufacturer to manufacturer. For example, some 4.7 µF/

10V devices tested showed typical values in the range of 0.5

-1

Ω, but values as high as 6Ω have been seen.

It should also be noted that the ESR typically increases

about 2X - 3X when going from +125˚C down to −40˚C.

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