EN/LZT 146 051 R7A Ericsson Power Modules, February 2007
PKM 4000E PI Datasheet
Thermal Consideration
General
The PKM 4000E Series DC/DC converters are designed
to operate in a variety of thermal environments, however
sufficient cooling should be provided to help ensure reliable
operation . Heat is removed by conduction, convection and
radiation to the surrounding environment . Increased airflow
enhances the heat transfer via convection . The available load
current vs . ambient air temperature and airflow at Vin=53 V
for each model is according to the information given under
the output section . The test is done in a wind tunnel with a
cross section of 305x305mm, the DC/DC converter vertically
mounted on a 8 layer PCB with a size of 254x254mm .
Proper cooling can be verified by measuring the temperature
of selected devices . Peak temperature can occur at position
P1 and P2 . The temperature at these positions should not
exceed the recommended max values .
Calculation of ambient temperature
By using the thermal resistance the maximum allowed
ambient temperature can be calculated .
1 . The powerloss is calculated by using the formula
((1/
η) - 1) × output power = power losses .
η = efficiency of converter. E .g 89% = 0 .89
2 . Find the value of the thermal resistance for each product in
the diagram by using the airflow speed at the output section
of the converter. Take the thermal resistance x powerloss to
get the temperature increase .
3 . Max allowed calculated ambient temperature is: Max
TPCB of DC/DC converter – temperature increase .
E .g PKM 4510E PI at 1m/s:
B . 6 .1W × 5 .5°C/W = 33 .6°C
C .110°C - 33 .6°C = max ambient temperature is 76 .4°C
The real temperature will be dependent on several factors,
like PCB size and type, direction of airflow, air turbulence
etc . It is recommended to verify the temperature by testing .
A . ((
) - 1) × 49 .5W = 6 .1W
1
0 .89
Position
Device
Tcritical
Max Value
P1
Transformer
Tcore
110C
P2
Mosfet
Tsurface
110C