LOAD CURRENT (A)

STABLE REGION

0

1

2

3

.001

.01

0.1

1.0

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LP3873, LP3876

SNVS220E – NOVEMBER 2002 – REVISED APRIL 2013

www.ti.com

APPLICATION HINTS

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 of at least 1µF is required. Ceramic or Tantalum may be used, and

capacitance may be increased without limit

OUTPUT CAPACITOR: An output capacitor is required for loop stability. It must be located less than 1 cm from

the device and connected directly to the output and ground pins using traces which have no other currents

flowing through them (see PCB LAYOUT section).

The minimum value of the output capacitance that can be used for stable full-load operation is 10 µF, but it may

be increased without limit. The output capacitor must have an ESR value as shown in the stable region of the

curve (below).

Figure 22. ESR Curve

SELECTING A CAPACITOR

It is important to note that capacitance tolerance and variation with temperature must be taken into consideration

when selecting a capacitor so that the minimum required amount of capacitance is provided over the full

operating temperature range. In general, a good Tantalum capacitor will show very little capacitance variation

with temperature, but a ceramic may not be as good (depending on dielectric type). Aluminum electrolytics also

typically have large temperature variation of capacitance value.

Equally important to consider is a capacitor's ESR change with temperature: this is not an issue with ceramics,

as their ESR is extremely low. However, it is very important in Tantalum and aluminum electrolytic capacitors.

Both show increasing ESR at colder temperatures, but the increase in aluminum electrolytic capacitors is so

severe they may not be feasible for some applications (see CAPACITOR CHARACTERISTICS Section).

CAPACITOR CHARACTERISTICS

CERAMIC: For values of capacitance in the 10 to 100 µF range, ceramics are usually larger and more costly

than tantalums but give superior AC performance for bypassing high frequency noise because of very low ESR

(typically less than 10 m

Ω). However, some dielectric types do not have good capacitance characteristics as a

function of voltage and temperature.

Z5U and Y5V dielectric ceramics have capacitance that drops severely with applied voltage. A typical Z5U or

Y5V capacitor can lose 60% of its rated capacitance with half of the rated voltage applied to it. The Z5U and Y5V

also exhibit a severe temperature effect, losing more than 50% of nominal capacitance at high and low limits of

the temperature range.

X7R and X5R dielectric ceramic capacitors are strongly recommended if ceramics are used, as they typically

maintain a capacitance range within ±20% of nominal over full operating ratings of temperature and voltage. Of

course, they are typically larger and more costly than Z5U/Y5U types for a given voltage and capacitance.

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