WPMDH1100601 / 171010601
MagI3C Power Module
VDRM – Variable Step Down Regulator Module
Step 3 Select the input capacitor (CIN)
The MagI³C power module contains an internal 0.47μF input ceramic capacitor. The module requires additional, external
input capacitance to handle the input current ripple. This input capacitance should be located as close as possible to the
MagI³C power module. Input capacitor selection is generally based on different requirements. The first criteria is the input
current ripple. Worst case input current ripple rating is dictated by the equation:
1
2
D
VOUT
VIN
√
∙ IOUT ∙
IC
≈
(6)
where D≈
INRMS
1-D
As a point of reference, the worst case current ripple will occur when the module is presented with full load current and when
VIN = 2 x VOUT
.
Recommended minimum input capacitance is 10µF (including derating) ceramic with a voltage rating at least 25% higher
than the maximum applied input voltage for the application. It is strongly recommended to pay attention to the voltage and
temperature deratings of the capacitor selected. It should be noted that current ripple rating of ceramic capacitors may be
missing from the capacitor data sheet and you may have to contact the capacitor manufacturer for this rating.
The second criteria is the input voltage ripple.
If the system design requires a certain minimum value of peak-to-peak input voltage ripple (VIN ripple) then the following
equation may be used:
ꢁ
ꢂ
IOUT ∙ D ∙ 1-D
CIN≥
(7)
fSW(CCM) ∙ VIN ripple
As example, if ΔVIN is 1% of VIN for a 24V input to 3.3V output application, and fSW = 400 kHz this leads:
3.3V
24V
400000 ∙ 0.240V
3.3V
24V
1A ∙
∙ (1–
)
CIN
≥
CIN ≥1.25μF
Additional bulk capacitance with higher ESR may be required to damp any resonant effects between the input capacitance
and parasitic inductance of the incoming supply lines.
we-online.com
Würth Elektronik eiSos GmbH & Co. KG – Data Sheet Rev. 1.0
© September 2017
20/54
WURTH [ WURTH ELEKTRONIK GMBH & CO. KG, GERMANY. ]
