LOAD CURRENT (A)

STABLE REGION

0

1

2

3

.001

.01

0.1

1.0

10

LP3853, LP3856

SNVS173G – FEBRUARY 2003 – REVISED APRIL 2013

www.ti.com

APPLICATION INFORMATION

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 10µF 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 amount of output capacitance that can be used for stable operation is 10µF. For general usage

across all load currents and operating conditions, the part was characterized using a 10µF Tantalum input

capacitor. The minimum and maximum stable ESR range for the output capacitor was then measured which kept

the device stable, assuming any output capacitor whose value is greater than 10µF (see Figure 28 below).

It should be noted that it is possible to operate the part with an output capacitor whose ESR is below these limits,

assuming that sufficient ceramic input capacitance is provided. This will allow stable operation using ceramic

output capacitors (see next section).

OPERATION WITH CERAMIC OUTPUT CAPACITORS

LP385X voltage regulators can operate with ceramic output capacitors if the values of input and output

capacitors are selected appropriately. The total ceramic output capacitance must be equal to or less than a

specified maximum value in order for the regulator to remain stable over all operating conditions. This maximum

amount of ceramic output capacitance is dependent upon the amount of ceramic input capacitance used as well

as the load current of the application. This relationship is shown in Figure 29, which graphs the maximum stable

value of ceramic output capacitance as a function of ceramic input capacitance for load currents of 1A, 2A, and

3A. For example, if the maximum load current is 1A, a 10µF ceramic input capacitor will allow stable operation

for values of ceramic output capacitance from 10µF up to about 500µF.

10

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