Ericsson Internal
PRODUCT SPECIFICATION
4 (6)
Prepared (also subject responsible if other)
No.
EJANLLI
3/1301-BMR 638/2 Uen
Approved
Checked
Date
Rev
Reference
SEC/D (Julia You)
ECHWANG
2008-10-24
E
Thermal Consideration
General
The PKY converters are designed to operate in different
thermal environments and sufficient cooling must be provided
to ensure reliable operation.
Cooling of the PKY series power modules is achieved mainly
by conduction from the baseplate to a heatsink (“cold wall”).
If the baseplate temperature is kept below +100°C, the
module can deliver full output power at ambient temperature
up to +85°C without forced airflow cooling.
The PKY series power modules can also operate without a
heatsink but sufficient airflow must be provided. The Output
Current Derating graph found in the Output section for each
model provides the available output current vs. ambient air
temperature and air velocity at Vin = 27 V.
The DC/DC converter is tested on a 254 x 254 mm,
35 μm (1 oz), 8-layer test board mounted vertically in a wind
tunnel with a cross-section of 305 x 305 mm.
Proper cooling of the DC/DC converter can be verified by
measuring the temperature at positions P1…P5. The
temperature at these positions should not exceed the max
values provided in the table below.
Note that the max value is the absolute maximum rating
(non destruction) and that the electrical Output data is
guaranteed up to Tref +100°C.
See Design Note 019 for further information.
Position
Device
Designation
max value
P1
PCB
125 C
P2
Transformer
M1
120 C
P3
Baseplate
Tref
100 C
P4
Diode
D15
120 C
P5
MOSFET
T16
120 C
Definition of reference temperature (Tref)
The reference temperature is used to monitor the temperature
limits of the product. Temperatures above maximum Tref are
not allowed and may cause degradation or permanent
damage to the product. Tref is also used to define the
temperature range for normal operating conditions.
Tref is defined by the design and used to guarantee safety
margins, proper operation and high reliability of the module.
Calculation of the Maximum 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 (Pd).
η = efficiency of converter. E.g 94 % = 0.94
2. Find the thermal resistance (Rth) in the Thermal Resistance
graph found in the Output section for each model.
Calculate the temperature increase (ΔT).
ΔT = Rth x Pd
3. Max allowed ambient temperature is:
Max Tref - ΔT.
E. g. PKY 2616 PI at 1m/s:
1. ((
) -
1) × 600 W = 38.3 W
2. 38.3 W × 1.9°C/W = 73°C
3. 100 °C - 73°C = max ambient temperature is 27°C
The actual temperature will be dependent on several factors
such as the PCB size, number of layers and direction of
airflow.
The above calculations of the maximum ambient temperature
are based on the thermal resistance of the PKY module
without a heatsink.
1
0.94
E
PKY 2000 PI series
DC/DC converters, Input 18-36 V, Output 21.5 A/600 W
EN/LZT 146 385 R2A Oct 2008
Ericsson Power Modules AB
Technical Specication
12