Datasheet
Application Information ST1S15
16/28 DocID023280 Rev 3
8 Application Information
8.1 Input and output capacitor
It is recommended to use ceramic capacitors with X5R or X7R dielectric and low ESR. The
input capacitor is used to filter any disturbance present in the input line and to obtain stable
operation. The output capacitor is very important to satisfy the output voltage ripple
requirement.
The output voltage ripple (V
OUT_RIPPLE
), in continuous mode, must be calculated:
Equation 1
where ΔI
L
is the ripple current and f
SW
is the switching frequency.
The use of ceramic capacitors with voltage ratings in the range higher than 1.5 times the
maximum input or output voltage is recommended.
8.2 Inductor
The inductor is the key passive component for switching converters. The internal
compensation is optimized to operate with an output filter of L = 0.47 µH and C
OUT
= 4.7 µF.
In addition to the inductance value, in order to avoid saturation, the maximum saturation
current of the inductor must be higher than that of the I
PEAK
.
The peak current of the inductor must be calculated as:
Equation 2
The following inductor p/ns from different suppliers have been tested in the ST1S15
converters.
L
ESLV
fC8
1
ESRIV
IN
SWOUT
LRIPPLE_OUT
×
+
××
+×Δ=
Table 8. Inductors
Manufacturers p/ns Dimensions (in mm)
Murata
LQM21PNR47MC0D 2.0 x 1.25 x 0.5
LQM21PNR54MG0D 2.0 x 1.25 x 0.5
LQH32PNR47NN0L 3.2 x 2.7 x 1.55
TDK
MLP2012SR47T 2.0 x 1.25 x 0.5
VLS2010ET-1R0N 2.0 x 2.0 x 1.0
LfV2
)VV(V
II
SWMAX_IN
OUTMAX_INOUT
OUTPEAK
×××
−×
+=