Datasheet

LP2982

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SNVS128J –MARCH 2000–REVISED APRIL 2013

APPLICATION HINTS

EXTERNAL CAPACITORS

Like any low-dropout regulator, the external capacitors used with the LP2982 must be carefully selected to

assure regulator loop stability.

Input Capacitor: An input capacitor whose value is ≥ 1 μF is required with the LP2982 (amount of capacitance

can be increased without limit).

This capacitor must be located a distance of not more than 0.5″ from the input pin of the LP2982 and returned to

a clean analog ground. Any good quality ceramic or tantalum can be used for this capacitor.

Output Capacitor: The output capacitor must meet both the requirement for minimum amount of capacitance

and E.S.R. (equivalent series resistance) value. Curves are provided which show the allowable ESR range as a

function of load current for various output voltages and capacitor values (refer to Figure 37 and Figure 38).

Important: The output capacitor must maintain its ESR in the stable region over the full operating temperature 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.

This capacitor should be located not more than 0.5″ from the output pin of the LP2982 and returned to a clean

analog ground.

Low-current Operation: In applications where the load current is < 1 mA, special consideration must be given to

the output capacitor.

Circuitry inside the LP2982 is specially designed to reduce operating (quiescent) current at light loads down to

about 65 μA.

The mode of operation which yields this very low quiescent current also means that the output capacitor ESR is

critical.

For optimum stability and minimum output noise, it is recommended that a 10Ω resistor be placed in series with

the output capacitor in any applications where I

< 1 mA.

CAPACITOR CHARACTERISTICS

Tantalum: Tantalum capacitors are the best choice for use with the LP2982. Most good quality tantalum can be

used with the LP2982, but check the manufacturer's data sheet to be sure the ESR is in range.

It is important to remember that ESR increases sharply at lower temperatures (< 10°C) and a capacitor that is

near the upper limit for stability at room temperature can cause instability when it gets cold.

In applications which must operate at very low temperatures, it may be necessary to parallel the output tantalum

capacitor with a ceramic capacitor to prevent the ESR from going up too high (see next section for important

information on ceramic capacitors).

Ceramic: Ceramic capacitors are not recommended for use at the output of the LP2982. This is because the

ESR of a ceramic can be low enough to go below the minimum stable value for the LP2982. A good 2.2 μF

ceramic was measured and found to have an ESR of about 15 mΩ, which is low enough to cause oscillations.

If a ceramic capacitor is used on the output, a 1Ω resistor should be placed in series with the capacitor.

Aluminum: Because of large physical size, aluminum electrolytic are not typically used with the LP2982. They

must meet the same ESR requirements over the operating temperature range, which is more difficult because of

their large increase in ESR at cold temperature.

An aluminum electrolytic can exhibit an ESR increase of as much as 50X when going from 20°C to −40°C. Also,

some aluminum electrolytic are not operational below −25°C because the electrolyte can freeze.

Product Folder Links: LP2982