EN63A0QI
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 EN63A0QI DC-DC converter is
packaged in an 10x11x3mm 76-pin QFN package.
The QFN package is constructed with copper lead
frames that have exposed thermal pads. The
exposed thermal pad on the package should be
soldered directly on to a copper ground pad on the
printed circuit board (PCB) to act as a heat sink.
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
150°C.
PIN = POUT / η
PIN ≈ 21.6W / 0.85 ≈ 25.41W
The power dissipation (PD) is the power loss in the
system and can be calculated by subtracting the
output power from the input power.
PD = PIN – POUT
≈ 25.41W – 21.6 ≈ 3.81W
With the power dissipation known, the temperature
rise in the device may be estimated based on the
theta JA value (θJA). The θJA parameter estimates
how much the temperature will rise in the device for
every watt of power dissipation. The EN63A0QI has
a θJA value of 14 ºC/W without airflow.
Determine the change in temperature (∆T) based
on PD and θJA.
∆T = PD x θJA
∆T ≈ 3.81W x 14°C/W = 53.36°C ≈ 53°C
The following example and calculations illustrate
the thermal performance of the EN63A0QI.
Example:
The junction temperature (TJ) of the device is
approximately the ambient temperature (TA) plus
the change in temperature. We assume the initial
ambient temperature to be 25°C.
VIN = 5V
VOUT = 1.8V
TJ = TA + ∆T
IOUT = 12A
TJ ≈ 25°C + 53°C ≈ 78°C
First calculate the output power.
POUT = 1.8V x 12A = 21.6W
The maximum operating junction temperature
(TJMAX) of the device is 125°C, so the device can
operate at a higher ambient temperature. The
maximum ambient temperature (TAMAX) allowed can
be calculated.
Next, determine the input power based on the
efficiency (η) shown in Figure 8.
TAMAX = TJMAX – PD x θJA
≈ 125°C – 53°C ≈ 72°C
Efficiency vs. Output Current
100
90
The maximum ambient temperature the device can
reach is 72°C given the input and output conditions.
Note that the efficiency used in this example is at
85°C ambient temperature and is a worst case
condition. Refer to the de-rating curves in the
Typical Performance Curves section.
80
70
~85%
60
50
40
30
CONDITIONS
VIN = 5.0V
TA = 85 C
20
10
0
VOUT = 1.8V
0
1
2
3
4
5
6
7
8
9
10 11 12
OUTPUT CURRENT(A)
Figure 8: Efficiency vs. Output Current
For VIN = 5V, VOUT = 1.8V at 12A, η ≈ 85%
η = POUT / PIN = 87% = 0.85
Enpirion 2012 all rights reserved, E&OE
Enpirion Confidential
www.enpirion.com, Page 19
07077
May 9, 2012
Rev: C
ENPIRION [ ENPIRION, INC. ]
