LP3853ET-33 Datasheet, PDF (10/25 Pages) Texas Instruments – LP3853/LP3856 3A Fast Response Ultra Low Dropout Linear Regulators

LP3853, LP3856
SNVS173G – FEBRUARY 2003 – REVISED APRIL 2013
APPLICATION INFORMATION
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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).
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1.0
STABLE REGION
COUT > 10PF
0.1
.01
.001
0
1
2
3
LOAD CURRENT (A)
Figure 28. ESR Curve for C_OUT (with 10µF Tantalum Input Capacitor)
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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