LP2980-ADJ Datasheet, PDF (7/9 Pages) National Semiconductor (TI) – Micropower SOT, 50 mA Ultra Low-Dropout Adjustable Voltage Regulator

Typical Performance Characteristics Unless otherwise specified: T_A = 25˚C, V_IN = V_O(NOM) + 1V,
I_L = 1 mA, ON/OFF pin tied to V_IN, R_ADJ = 86.6k, and test circuit is as shown in Basic Application Circuit. (Continued)
Ripple Rejection
Application Hints
DS100001-21
EXTERNAL CAPACITORS
Like any low-dropout regulator, the external capacitors must
be selected carefully to assure regulator loop stability.
INPUT CAPACITOR: An input capacitor whose value is
≥1 µF is required (the amount of capacitance may be in-
creased without limit).
Any good quality Tantalum or Ceramic capacitor may be
used here. The capacitor must be located not more than 0.5"
from the input pin and returned to a clean analog ground.
OUTPUT CAPACITOR: The output capacitor must meet
both the requirement for minimum amount of capacitance
and E.S.R. (Equivalent Series Resistance) for stable opera-
tion.
Curves are provided below which show the allowable ESR of
the output capacitor as a function of load current for both
2.2 µF and 4.7 µF. A solid Tantalum capacitor is the best
choice for the output.
2.2 µF ESR Curves
DS100001-22
4.7 µF ESR Curves
DS100001-23
IMPORTANT: The output capacitor must maintain its ESR in
the stable region over the full operating temperature range to
assure stability. Also, capacitor tolerance and variation with
temperature must be considered to assure the minimum
amount of capacitance is provided at all times.
Note that this capacitor must be located not more than 0.5”
from the output pin and returned to a clean analog ground.
FEED-FORWARD CAPACITOR: A 7 pF feed-forward ca-
pacitor is required (see Basic Application Circuit). The func-
tion of this capacitor is to provide the lead compensation
necessary for loop stability.
A temperature-stable ceramic capacitor (type NPO or COG)
should be used here.
CAPACITOR CHARACTERISTICS
TANTALUM: The best capacitor choice for the LP2980-ADJ
output is solid Tantalum. The ESR of a good quality Tantalum
is almost perfectly centered in the middle of the “stable”
range of the ESR curve (about 0.5Ω–1Ω).
The temperature stability of Tantalums is typically very good,
with a total variation of only about 2:1 over the temperature
range of −40˚C to +125˚C (ESR increases at colder tem-
peratures).
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