Datasheet

MAX. ALLOWABLE CERAMIC
OUTPUT CAPACITANCE (PF)
CERAMIC INPUT CAPACITANCE (PF)
100
1000
10
100
I
L
= 1.5A
C
OUT
ESR (:)
LOAD CURRENT (A)
STABLE REGION
C
OUT
> 10 PF
0
1
2
.001
.01
0.1
1.0
10
LP3852, LP3855
SNVS174G –FEBRUARY 2003–REVISED APRIL 2013 www.ti.com
Figure 21. 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 the 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 22, which graphs the maximum stable
value of ceramic output capacitance as a function of ceramic input capacitance for load currents of 1.5A.
Figure 22. Maximum Ceramic Output Capacitance vs Ceramic Input Capacitance
If the maximum load current is 1.5A and a 10µF ceramic input capacitor is used, the regulator will be stable with
ceramic output capacitor values from 10µF up to about 150µF. When calculating the total ceramic output
capacitance present in an application, it is necessary to include any ceramic bypass capacitors connected to the
regulator output.
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.
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