WPMDH1100601 / 171010601
MagI3C Power Module
VDRM – Variable Step Down Regulator Module
Step 4 Select output capacitor (COUT
)
L
HS Mosfet
IL
Iout
VCOUT
COUT
CIN
VIN
VOUT
RLoad
LS Mosfet
ESR
VESR
None of the required output capacitors are integrated within the module. A general recommendation in order to guarantee a
stable behavior is to place at least a capacitance of 10µF (MLCC recommended) at the output.
The output capacitor must meet the worst case RMS current rating, as calculated by equation (8):
∆IL
IC
=
(8)
(9)
OUTRMS
ꢄ12
where ∆IL is the inductor current ripple calculated with the equation (9)
VOUT ∙ (VIN-VOUT
fSW ∙ L ∙ VIN
)
∆IL=
Selection by output voltage ripple requirements
The output capacitor should be selected in order to minimize the output voltage ripple and provide a stable voltage at the
output. Under steady state conditions, the voltage ripple observed at the output can be defined as:
1
VOUT ripple=∆IL ∙ ESR+∆IL ∙
(10)
8∙fSW∙COUT
Very low ESR capacitors, like ceramic and polymer electrolytic, are recommended. If a low ESR capacitor is selected,
equation (10) can be simplified and a first condition for the minimum capacitance value can be derived:
∆IL
COUT
≥
(11)
8 ∙ VOUT ripple ∙ fSW
Beyond that, the additional capacitance will reduce the output voltage 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 (e.g.
MLCC X7R up to -50%).
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Würth Elektronik eiSos GmbH & Co. KG – Data Sheet Rev. 1.0
© September 2017
21/54
WURTH [ WURTH ELEKTRONIK GMBH & CO. KG, GERMANY. ]
