Datasheet
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Würth Elektronik eiSos GmbH & Co. KG - Data Sheet - REV 1.0
11/29
WPMDH1200601 / 171020601
MagI³C Power Module
VDRM - Variable Step Down Regulator Module
DESIGN FLOW
The approximate formula for determining the DCM/CCM boundary is as follows:
(7)
Following is a typical waveform showing the boundary condition.
Inductor Current
V
IN
= 24V, V
OUT
= 3.3V
2 µs/Div
500 mA/Div
Transition Mode
Operation
I
OUT
= 0.35A
The value of the inductor inside the module is 10μH. This was chosen as a good balance between low and high input
voltage applications. The main parameter affected by the inductor is the amplitude of the inductor ripple current (I
LR
).
I
LR
peak to peak can be calculated with:
(8)
Where V
IN
is the maximum input voltage and f
SW
is the previously selected value in equation (2).
If the output current I
OUT
is determined by assuming that I
OUT
= I
L
, the higher and lower peak of I
LR
can be determined.
Be aware that the lower peak of I
LR
must be positive if CCM operation is required.
Step 3. Select Input Capacitor (C
IN
)
The MagI³C power module contains an internal 0.47μF input ceramic capacitor. Additional input capacitance is
required external to the MagI³C power module to handle the input ripple current of the application. This input
capacitance should be located as close as possible to the MagI³C power module. Input capacitor selection is
generally directed to satisfy the input ripple current requirements rather than by capacitance value. Worst case input
ripple current rating is dictated by the equation:
(9)
where
(As a point of reference, the worst case ripple current will occur when the module is presented with full load current
and when
).
Recommended minimum input capacitance is 10µF 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.