20

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

T

ensure the CXA LED is being operated within its designed limits. Please refer to page 22 for the Operating Limit specification.

There is no need to calculate for T

ambient (T

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 CXA3590 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 each 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

CXA3590

0.01

0.10

1.00

10.00

100.00

400

800

1200

1600

2000

2400

2800

3200

3600

Current (mA)

Ta = 25 °C

Ta = 55 °C

Ta = 85 °C

Ta = 105 °C

36 V