Datasheet
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© May 2016
Würth Elektronik eiSos GmbH & Co. KG - Data Sheet - REV 1.0
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WPMDU1251501 / 171021501
MagI³C Power Module
VDRM - Variable Step Down Regulator Module
Step 3 Select input capacitor (C
IN
)
The WPMDU1251501 MagI³C power module contains no internal input capacitors. Therefore an external input capacitance
placed directly at the V
IN
pin is required to handle the input ripple current of the application. 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:
(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 * V
OUT
).
If the system design requires a certain minimum value of peak-to-peak input ripple voltage (ΔV
IN
) be maintained then the
following equation may be used.
If ΔV
IN
is 1% of V
IN
for a 24V input to 5V output application this equals 240 mV and f
SW
= 500kHz.
Recommended minimum input capacitance is 4.4µF X7R 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.
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.