EP53A8LQA Datasheet, PDF (17/21 Pages) Altera Corporation – Integrated Inductor

Thermal Considerations
Thermal considerations are important power supply
design facts that cannot be avoided in the real
world. Whenever there are power losses in a
system, the heat that is generated by the power
dissipation needs to be accounted for. The Enpirion
PowerSoC helps alleviate some of those concerns.
The Enpirion EP53A8xQA DC-DC converter is
packaged in a 3x3x1.1mm 16-pin QFN package.
The recommended maximum junction temperature
for continuous operation is 125°C. Continuous
operation above 125°C may reduce long-term
reliability. The device has a thermal overload
protection circuit designed to turn off the device at
an approximate junction temperature value of
155°C.
The following example and calculations illustrate
the thermal performance of the EP53A8xQA.
Example:
V_IN = 5V
V_OUT = 3.3V
I_OUT = 1A
First calculate the output power.
P_OUT = 3.3V x 1A = 3.3W
Next, determine the input power based on the
efficiency (η) shown in Figure 9.
Efficiency vs. I_OUT (V_IN = 5.0V)
95
90
85
80
75
86.5%
70
65
60
55
50
45
CONDITIONS
VOUT = 3.3V
40
V_IN = 5V
35
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
OUTPUT CURRENT (A)
Figure 9. Efficiency vs. Output Current
For V_IN = 5V, V_OUT = 3.3V at 1A, η ≈ 86.5%
η = P_OUT / P_IN = 86.5% = 0.865
P_IN = P_OUT / η
EP53A8LQA/EP53A8HQA
P_IN ≈ 3.3W / 0.865 ≈ 3.815W
The power dissipation (P_D) is the power loss in the
system and can be calculated by subtracting the
output power from the input power.
P_D = P_IN – P_OUT
≈ 3.815W – 3.3W ≈ 0.515W
With the power dissipation known, the temperature
rise in the device may be estimated based on the
theta JA value (θ_JA). The θ_JA parameter estimates
how much the temperature will rise in the device for
every watt of power dissipation. The EP53A8xQA
has a θ_JA value of 80 ºC/W without airflow.
Determine the change in temperature (ΔT) based
on P_D and θ_JA.
ΔT = P_D x θ_JA
ΔT ≈ 0.515W x 80°C/W = 41.2°C ≈ 41°C
The junction temperature (T_J) of the device is
approximately the ambient temperature (T_A) plus
the change in temperature. We assume the initial
ambient temperature to be 25°C.
T_J = T_A + ΔT
T_J ≈ 25°C + 41°C ≈ 66°C
The maximum operating junction temperature
(T_JMAX) of the device is 125°C, so the device can
operate at a higher ambient temperature. The
maximum ambient temperature (T_AMAX) allowed can
be calculated.
T_AMAX = T_JMAX – P_D x θ_JA
≈ 125°C – 41°C ≈ 84°C
The maximum ambient temperature (before de-
rating) the device can reach is 84°C given the input
and output conditions. Note that the efficiency will
be slightly lower at higher temperatures and this
calculation is an estimate.
10366
July 21, 2015
www.altera.com/enpirion, Page 17
Rev D