Datasheet
1515
Copyright © 2013-2015 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree
®
, the Cree logo, XLamp
®
and EasyWhite
®
are registered trademarks of Cree,
Inc. UL
®
and the UR logo are registered trademarks of UL LLC.
15
XLamp
®
CXa1816 LED
THERMAL DESIGN
The CXA family of LED arrays can include over a hundred different LED die inside one package, and thus over a hundred different junction
temperatures (T
J
). Cree has intentionally removed junction‑temperature‑based operating limits and replaced the commonplace maximum
T
J
calculations with maximum ratings based on forward current (I
F
) and case temperature (Tc). No additional calculations are required to
ensure the CXA LED is being operated within its designed limits. Please refer to page 2 for the Operating Limit specication.
There is no need to calculate for T
J
inside the package, as the thermal management design process, specically from solder point (T
SP
) to
ambient (T
a
), remains identical to any other LED component. For more information on thermal management of Cree XLamp LEDs, please
refer to the Thermal Management application note. For CXA soldering recommendations and more information on thermal interface
materials (TIM) and connection methods, please refer to the Cree XLamp CX Family LEDs soldering and handling document. The CX
Family LED Design Guide provides basic information on the requirements to use Cree XLamp CXA LEDs successfully in luminaire designs.
To keep the CXA1816 LED at or below the maximum rated Tc, the case to ambient temperature
thermal resistance (R_c‑a) must be at or below the maximum R_c‑a value shown on the following
graph, depending on the operating environment. The y‑axis in the graph is a base 10 logarithmic
scale.
As the gure at right shows, the R_c‑a value is the sum of the thermal resistance of the TIM (R_tim)
plus the thermal resistance of the heat sink (R_hs).
R_j-c
Tc
R_tim
R_hs
Ta
R_j-c
Tc
R_c-a
Ta
CXA1816
0.01
0.10
1.00
10.00
100.00
250 380 510 640 770 900
Maximum R_c-a
Current (mA)
Ta = 25 °C
Ta = 55 °C
Ta = 85 °C
Ta = 105 °C