Data Sheet
we-online.com
Würth Elektronik eiSos GmbH & Co. KG - Data Sheet - REV 1.0
16/31
WPMDH1102401 / 171012401
MagI³C Power Module
VDRM - Variable Step Down Regulator Module
DESIGN FLOW
(16)
V
UVLO (EXTERN)
= User programmable voltage threshold to turn the module ON/OFF.
The EN pin is internally pulled up to V
IN
and can be left floating for always-on operation. However, it is good practice
to use the enable divider and turn on the regulator when V
IN
is close to reaching its nominal value. This will guarantee
smooth startup and will prevent overloading the input supply.
Determine power losses and thermal requirements of the board
For example:
T
AMB(MAX)
is the maximum air temperature surrounding the module.
T
J(MAX)
is the maximum value of the junction temperature according to the “OPERATING CONDITIONS” limit.
The goal of the calculation is to determine the characteristics of the required heat sink. In case of a surface mounted
module this would be the PCB (number of layers, copper area and thickness). These characteristics are reflected in
the value of the thermal resistance case to ambient: Ɵ
CA
.
The basic formula for calculating the operating junction temperature T
J
of a semiconductor device is as follows:
(17)
P
IC-LOSS
are the total power losses within the module IC and are related to the operating conditions.
Ɵ
JA
is the thermal resistance junction to ambient and calculated as:
(18)
Ɵ
JC
is the thermal resistance junction to case.
Combining equation (17) and (18) results in the maximum case-to-ambient thermal resistance:
(19)
From section ”THERMAL SPECIFICATIONS“ the typical thermal resistance from junction to case (Ɵ
JC
) is defined
as 1.9 °C/W. Use the 85°C power dissipation curves in the “TYPICAL PERFORMANCE CURVES“ section to
estimate the P
IC-LOSS
for the application being designed.