Datasheet

Application information ST1S40
16/29 DocID17928 Rev 5
In Table 7 below some inductor part numbers are listed.
6.3 Output capacitor selection
The current in the output capacitor has a triangular waveform which generates a voltage
ripple across it. This ripple is due to the capacitive component (charge or discharge of the
output capacitor) and the resistive component (due to the voltage drop across its ESR). So
the output capacitor must be selected in order to have a voltage ripple compliant with the
application requirements.
The amount of the voltage ripple can be calculated starting from the current ripple obtained
by the inductor selection.
Equation 21
For ceramic (MLCC) capacitors the capacitive component of the ripple dominates the
resistive one. Whilst for electrolytic capacitors the opposite is true.
Since the compensation network is internal, the output capacitor should be selected in order
to have a proper phase margin and then a stable control loop.
The equations of Section 5.2 help to check loop stability given the application conditions,
the value of the inductor, and of the output capacitor.
In Table 8 some capacitor series are listed.
Table 7. Inductors
Manufacturer Series Inductor value (H) Saturation current (A)
Coilcraft
XPL7030 2.2 to 4.7 6.8 to 10.5
MSS1048 2.2 to 6.8 4.14 to 6.62
MSS1260 10 5.5
Wurth
WE-HC/HCA 3.3 to 4.7 7 to 11
WE-TPC typ XLH 3.6 to 6.2 4.5 to 6.4
WE-PD type L 10 5.6
TDK RLF7030T 2.2 to 4.7 4 to 6
Table 8. Output capacitors
Manufacturer Series Cap value (F) Rated voltage (V) ESR (m)
MURATA
GRM32 22 to 100 6.3 to 25 < 5
GRM31 10 to 47 6.3 to 25 < 5
PANASONIC
ECJ 10 to 22 6.3 < 5
EEFCD 10 to 68 6.3 15 to 55
SANYO TPA/B/C 100 to 470 4 to 16 40 to 80
TDK C3225 22 to 100 6.3 < 5
V
OUT
ESR I
MAX

I
MAX
8C
OUT
f
SW

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