WPMDH1100601 / 171010601
MagI3C Power Module
VDRM – Variable Step Down Regulator Module
Example
The following application conditions are used as an example to show how to calculate a suitable COUT value:
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VIN = 24V
VOUT = 5V
RON = 75kΩ
load transient from 0.5A to 1A and vice versa (∆IOUT = 0.5A)
max allowed undershoot or overshoot ∆VOUT = 100mV
The COUT can be calculated using the equation (15) on page 24. This equation provides two possible values depending on
whether td is calculated for a positive load transient (generating a VOUT drop) or for a negative load transient (resulting in a
VOUT overshoot).
In case of positive load transient: td = 920ns and COUT ≥ 4.1µF
In case of negative load transient: td = 2.18µs and COUT ≥ 9.6µF
A combination of 10µF (Würth Elektronik, part number 885012109008) + 4.7µF (885012109008) MLCC are selected. Some
margin from the calculated COUT value is recommended in order to take into account:
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Approximations within the equations to estimate td and COUT itself;
Tolerances and variations of some components and parameters involved in those equations (e.g. RON, tOFF-MIN, L, k,
etc.)
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Derating of the capacitors with DC applied voltage and temperature
The use of two MLCCs in parallel contributes to the further reduction of the total ESR.
The load transients with the selected COUT can be tested using the setup depicted below:
VIN
VIN
VOUT
MagI³C Power
COUT
RLoad1
RLoad2
Module
10Ω
10Ω
GND
Q1
IOUT2
IOUT1
GND
we-online.com
Würth Elektronik eiSos GmbH & Co. KG – Data Sheet Rev. 1.0
© September 2017
26/54
WURTH [ WURTH ELEKTRONIK GMBH & CO. KG, GERMANY. ]
