PMB8510P View Datasheet(PDF) - Ericsson
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PMB8510P Datasheet PDF : 32 Pages
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The PMB 8000 series regulator can accept up to 8mF of
capacitive load on the output at full load. This gives <500
μF/A of IO. When using that large capacitance it is important
to consider the selection of output capacitors; the resulting
choke
behavior is a combination of the amount of capacitance and
ESR.
airflow
A combination of low ESR and output capacitance
exceeding 8mF for PMB 8818 can cause the regulator into
over current protection mode (hick-up) due to high start up
current. The output filter must therefore be designed without
exceeding the above stated capacitance levels if the ESR is
lower then
30-40 mW.
Test board
Parallel Operation
The PMB 8000 Series DC/DC regulators can be connected
in parallel with a common input. Paralleling is accomplished
by connecting the output voltage pins directly and using
a load sharing device on the input. Layout considerations
should be made to avoid load imbalance. For more details
on paralleling, please consult your local applications support.
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 88% = 0.88
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.
Thermal Considerations
General
The PMB 8000 Series DC/DC regulators 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. Proper cooling
can be verified by measuring the temperature
at the reference point (Tref).
3. Max allowed calculated ambient temperature is: Max
Tref of DC/DC regulator – temperature increase.
E.g 5 V output at 1 m/s, full load, 12 V in:
A. (( 1 ) - 1) × 80 W = 5.11 W
0.94
B. 5.11 W × 7.2 °C/W = 36.8 °C
C. 115 °C - 36.8 °C = max ambient temperature is 78.2 °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.
Tref (max 115 °C)
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The PMB 8000 thermal testing is performed with the
product mounted on an FR4 board 254 ����2�5�4��m�m���w�i�t�h�8�
layers of 35 µm copper. Airflow is perpendicular to the Tref
side.
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Thermal resistance vs. airspeed measured at the regulator.
PMB 8818T P Datasheet
30
EN/LZT 146 066 R2A © Ericsson Power Modules, April 2007
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