WPMDH1100601 / 171010601
MagI3C Power Module
VDRM – Variable Step Down Regulator Module
DETERMINE POWER LOSSES AND THERMAL REQUIREMENTS OF THE BOARD
This section provides an example of calculation of power losses and thermal design of the board.
As a starting point the following application conditions can be considered:
V =24V, VOUT=3.3V, IOUT=1A, TAꢁMAXꢂ =85°C and Tꢁ ꢂ=125°C
IN
J MAX
where TA is the maximum air temperature surrounding the module and TJ(MAX) is the maximum value of the junction
temperature according to the limits in the “OPERATING CONDITIONS” section on page 4.
The goal of the calculation is to determine the characteristics of the required heat sink. In the 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 case to ambient thermal resistance (θꢅꢆ).
The basic formula for calculating the operating junction temperature TJ of a semiconductor device is as follows:
TJ=PIC-LOSS ∙ θJA + TA
(19)
PIC-LOSS are the total power losses within the module´s IC and are related to the operating conditions.
ƟJA is the junction to ambient thermal resistance and calculated as:
θJA=θJC + θCA
(20)
ƟJC is the junction to case thermal resistance.
Combining equations (19) and (20) results in the maximum case-to-ambient thermal resistance:
TJ(MAX)-TA(MAX)
θCA(MAX)
<
- θJC
(21)
PIC-LOSS
From section ”THERMAL SPECIFICATIONS“ (page 4) the typical thermal resistance from junction to case (θꢅꢇ) is defined as
1.9 °C/W. Use the 85°C power dissipation curves in the “TYPICAL PERFORMANCE CURVES“ section (page 12) to
estimate the PIC-LOSS for the application being designed.
171010601 VIN = 24V, fSW =500kHz, TA = 25°C
1,00
0,80
640mW
0,60
Vout = 5V
Vout = 3.3V
0,40
Vout = 2.5V
Vout = 1.8V
0,20
0,00
0
0,25
0,5
0,75
1
Output Current [A]
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© September 2017
Würth Elektronik eiSos GmbH & Co. KG – Data Sheet Rev. 1.0
30/54
WURTH [ WURTH ELEKTRONIK GMBH & CO. KG, GERMANY. ]
