LP2986

SNVS137H – MARCH 1999 – REVISED APRIL 2013

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APPLICATION HINTS

WSON PACKAGE DEVICES

The LP2986 is offered in the 8 lead WSON surface mount package to allow for increased power dissipation

compared to the SOIC-8 and VSSOP-8. For details on WSON thermal performance as well as mounting and

soldering specifications, refer to the WSON MOUNTING section.

EXTERNAL CAPACITORS

Like any low-dropout regulator, external capacitors are required to assure stability. These capacitors must be

correctly selected for proper performance.

INPUT CAPACITOR: An input capacitor (

≥ 2.2 µF) is required between the LP2986 input and ground (amount of

capacitance may be increased without limit).

This capacitor must be located a distance of not more than 0.5” from the input pin and returned to a clean analog

ground. Any good quality ceramic or tantalum may be used for this capacitor.

OUTPUT CAPACITOR: The output capacitor must meet the requirement for minimum amount of capacitance

and also have an appropriate 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 (see ESR curves below).

Figure 34. ESR Curves For 5V Output

Figure 35. ESR Curves For 2.5V Output

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

range of the application to assure stability.

The minimum required amount of output capacitance is 4.7 µF. Output capacitor size can be increased without

limit.

It is important to remember that capacitor tolerance and variation with temperature must be taken into

consideration when selecting an output capacitor so that the minimum required amount of output capacitance is

provided over the full operating temperature range. A good Tantalum capacitor will show very little variation with

temperature, but a ceramic may not be as good (see next section).

CAPACITOR CHARACTERISTICS

TANTALUM: The best choice for size, cost, and performance are solid tantalum capacitors. Available from many

sources, their typical ESR is very close to the ideal value required on the output of many LDO regulators.

Tantalums also have good temperature stability: a 4.7 µF was tested and showed only a 10% decline in

capacitance as the temperature was decreased from +125°C to

−40°C. The ESR increased only about 2:1 over

the same range of temperature.

However, it should be noted that the increasing ESR at lower temperatures present in all tantalums can cause

oscillations when marginal quality capacitors are used (where the ESR of the capacitor is near the upper limit of

the stability range at room temperature).

CERAMIC: For a given amount of a capacitance, ceramics are usually larger and more costly than tantalums.

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