Datasheet
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Würth Elektronik eiSos GmbH & Co. KG - Data Sheet - REV 1.0
11/31
WPMDH1302401 / 171032401
MagI³C Power Module
VDRM - Variable Step Down Regulator Module
DESIGN FLOW
7 Steps to design the power application
The next 7 simple steps will show how to select the external components to design your power application:
1. Program output voltage
2. Set operating frequency with R
ON
3. Select input capacitor
4. Select output capacitor
5. Select soft-start capacitor
6. Select feed forward capacitor
7. Optional: Program under voltage lockout divider
R
ON
C
IN
RON
VIN
EN PGND SS
FB
VOUT
Module
R
FBT
R
FBB
C
SS
C
FF
C
OUT
AGND
1
2
3
EP
5
4
6
7
R
ENT
R
ENB
1.
2.
3. 4.
5.
6.
7.
V
IN
V
OUT
Step 1. Select Output Voltage (V
OUT
)
Output voltage is determined by a divider of two resistors connected between V
OUT
and ground. The midpoint of the
divider is connected to the FB input. The voltage at FB is compared to a 0.8V internal reference. In normal operation
an on-time cycle is initiated when the voltage on the FB pin falls below 0.8V. The high-side MOSFET on-time cycle
causes the output voltage to rise and the voltage at the FB to exceed 0.8V. As long as the voltage at FB is above
0.8V, on time cycles will not occur.
The ratio of the feedback resistors for a desired output voltage is:
(1)
These resistors should be chosen from values in the range of 1kΩ to 50kΩ.
A table of values for R
FBT
, R
FBB
, and R
ON
is included in the applications circuit.
Step 2. Select On-Time Resistor (R
ON
)
Many designs will begin with a desired switching frequency in mind. For that purpose the following equation can be
used.
(2)
The selection of R
ON
and f
SW(CCM)
must be confined by limitations in the on-time and off-time for the COT control
section. The on-time of the MagI³C power module timer is determined by the resistor R
ON
and the input voltage V
IN
. It
is calculated as follows:
(3)