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 21/48
Step 3 Select input capacitor (C
IN
)
The energy at the input of the power module is stored in the input capacitor. A small input capacitor (100nF) is integrated
inside the 1710x0302 MagI³C Power Module series, ensuring good EMI performance. Additional input capacitance is
required external to the power module to provide cycle-by-cycle switch current and to support load transients. The external
input capacitors must be placed directly at VIN pin. The input capacitor can be several capacitors in parallel. Input capacitor
selection is generally directed to satisfy the input ripple current requirements rather than by capacitance value. Input ripple
current rating is dictated by the equation:
I
≈
1
2
∗I
∗
D
1−D
(
2
)
whereD≈
V
V
As a point of reference, the worst case ripple current will occur when the module is presented with full load current and when
V
IN
= 2 x V
OUT
.
Recommended minimum input capacitance is 47µF X7R or X5R ceramic with a voltage rating at least 25% higher than the
maximum applied input voltage for the application. It is also recommended that attention be paid to the voltage and
temperature deratings of the capacitor selected. It should be noted that ripple current rating of ceramic capacitors may be
missing from the capacitor data sheet and you may have to contact the capacitor manufacturer for this rating.
If the system design requires a certain minimum value of peak-to-peak input ripple voltage (ΔV
IN
) then the following equation
may be used:
C
≥
I
∗D∗
(
1−D
)
f
∗∆V
(
3
)
whereD≈
V
V
CCM = continuousconductionmode
Additional bulk capacitance with higher ESR may be required to damp any resonant effects of the input capacitance and
parasitic inductance of the incoming supply lines.