0

0.2

0.4

0.6

0.8

LOAD CURRENT (A)

1

STABLE REGION

COUT > 10PF

.001

.01

0.1

1.0

10

LP3871, LP3874

SNVS225H – FEBRUARY 2003 – REVISED JUNE 2015

www.ti.com

Typical Applications (continued)

8.2.1 Design Requirements

For LP3871 and LP3874 typical applications, use the parameters listed in Table 1.

Table 1. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Input voltage

2.5 V to 7 V

Output voltage

2.5 V

Output current

0.8 A

Output capacitor

10 µF

Input capacitor

10 µF

Output capacitor ESR range

100 m

Ω to 4 Ω

8.2.2 Detailed Design Procedure

8.2.2.1 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 10

μF is required. Ceramic, tantalum, or Electrolytic capacitors

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 Layout Guidelines).

The minimum value of 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 equivalent series resistance (ESR) value as shown in

the stable region of the curve (Figure 13). Tantalum capacitors are recommended for the output capacitor.

Figure 13. ESR Curve

8.2.2.2 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).

12

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