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EN/LZT 146 201 R3A Ericsson Power Modules, February 2007
PKM 4000D Datasheet
Thermal Consideration
General
The PKM 4000D 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 305 x 305 mm, the
DC/DC converter vertically mounted on a 16 layer Pcb
with a size of 254 x 254 mm, each layer with 35 m (1
oz) copper. Proper cooling can be verified by measuring
the temperature of selected devices. Peak temperature
can occur at positions P1 - P4. The temperature at these
positions should not exceed the recommended max values.
Note that the recommended max value is the absolute
maximum rating (non destruction) and that the electrical
output data is guaranteed up to TPcb +90 °C.
Calculation of ambient temperature
By using the thermal resistance the maximum allowed
ambient temperature can be calculated.
1. The power loss is calculated by using the formula
((1/
η) - 1) × output power = power losses.
η = efficiency of converter. E.g 90% = 0.90
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.
B. 8 W × 4.8 °C/W = 38.4 °C
C. 120 °C - 38.4 °C = max ambient temperature is 81.6 °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) × 72 W = 8 W
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0.90
E.g PKM 4718GD PINB at 1m/s:
Position
Device
TC
Recommended
max value
P1
Pcb
120
°C
P2
Transistor
Tsurface
120
°C
P3
Transistor
Tsurface
120
°C
P4
Transformer
Tsurface
130
°C
Input side
Output side