LP2980LV Datasheet, PDF (10/14 Pages) National Semiconductor (TI) – Micropower SOT, 50 mA Low-Voltage Low-Dropout Regulator For Applications With Output Voltages < 2V

Application Hints (Continued)
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:
10109120
10 µF ESR Curves For 1.8V Output
10109118
2.2 µF ESR Curves For 1.8V Output
10109119
4.7 µF ESR Curves For 1.8V Output
www.national.com
10109121
15 µF ESR Curves For 1.8V Output
It should be noted that for the lower values of the output
capacitance (< 10 µF), it may be necessary to use a capaci-
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 mΩ), 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 2Ω +/− 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
- 1Ω, 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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