11

thErMaL DEsign

The CXB family of LED arrays can include over a hundred different LED die inside one package, and thus over a hundred different junction

temperatures (T

T

ensure the CXB LED is being operated within its designed limits. Please refer to page 2 for the Operating Limit specification.

There is no need to calculate for T

ambient (T

refer to the Thermal Management application note. For CXB 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 CXB LeDs successfully in luminaire designs.

To keep the CXB3050 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 figure 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

CXB3050

0.01

0.10

1.00

10.00

400

700

1000

1300

1600

1900

2200

2500

Current (mA)

Ta = 25 °C

Ta = 55 °C

Ta = 85 °C

Ta = 105 °C