Datasheet
WPMDB1400362Q / 171040302
MagI
3
C Power Module
VDRM – Variable Step Down Regulator Module
we-online.com Würth Elektronik eiSos GmbH & Co. KG – Data Sheet Rev. 1.0
© May 2016 22/48
Step 4 Select output capacitor (C
OUT
)
L
C
OUT
Rload
V
IN
V
O UT
I
L
I
out
HS Mosfet
ESR
V
ESR
V
COUT
LS Mosfet
C
IN
None of the required output capacitors are integrated within the module. The output capacitor must meet the worst case
RMS current rating of 0.5∗∆
, as calculated in equation (4).
∆I
=
V
∗(V
−V
)
f
∗L∗V
(4)
Selection by output voltage ripple requirements
The capacitor should be selected in order to minimize the output voltage and provide a stable voltage at the output.
Under steady state conditions, the voltage ripple observed at the output can be defined as:
V
=∆I
∗ESR+ ∆I
∗
1
8∙f
∙C
(5)
Very low ESR capacitors, like ceramic and polymer electrolytic, are recommended. If a low ESR capacitor is selected,
equation (4) can be simplified and a first condition for the minimum capacitance value can be derived:
C
≥
∆I
8∗V
∗f
(6)
Beyond that, additional capacitance will reduce output ripple as long as the ESR is low enough to permit it. Please consider
the derating of the nominal capacitance value due to temperature, aging and applied DC voltage (only for MLCC, e.g. X7R
up to -50%).