Datasheet

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®
, the Cree logo, XLamp
®
and EasyWhite
®
are registered
trademarks of Cree, Inc.
17
XLamp CXa1850 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specication.
Cree has measured the temperature at the bottom of the package, commonly referred to as the solder point (T
SP
),
and found this value to be equivalent to the temperature at the Tc location at the top of the package once the LED has
reached thermal equilibrium. There is no need to calculate for T
J
inside the package, as the thermal management design
process, specically from 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 XLamp Thermal Management application note at
www.cree.com/xlamp_app_notes/thermal_management. For CXA soldering recommendations and more information on
thermal interface materials (TIM) and connection methods, please refer to the Cree XLamp CXA Family LEDs soldering
and handling document at www.cree.com/xlamp_app_notes/CXA_SH.
To keep the CXA1850 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
CXA1850
0.01
0.10
1.00
10.00
500 750 1000 1250 1500 1750
Maximum R_c-a
Current (mA)
Ta = 25 °C
Ta = 55 °C
Ta = 85 °C
Ta = 105 °C
PRELIMINARY