19

ThErMaL DEsign

The CMT 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 CMT LED is being operated within its designed limits. LES temperature measurement provides additional verification of good

thermal design. Please refer to page 3 for the Operating Limit specification.

There is no need to calculate for T

ambient (T

refer to the Thermal Management application note. For CMT soldering recommendations and more information on thermal interface

materials (TIM), LeS temperature measurement, and connection methods, please refer to the Cree XLamp CM Family LeDs soldering and

handling document.

To keep the CMT1925 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

CMT1930

0.01

0.10

1.00

10.00

100.00

200

350

500

650

800

950

1100

1250

1400

1550

1700

1850

2000

Current (mA)

Ta = 25 °C

Ta = 55 °C

Ta = 85 °C

Ta = 105 °C