Application Note Heat Dissipation from NCSU03xx depending on Tj 1. Objective The light output of LEDs is reduced under the influence of heat generation. When LEDs are operated over the absolute maximum junction temperature (Tjmax), the performance is severely degraded. It is critical to design the heat dissipation not to exceed the Tjmax for NCSU03xx to achieve a high reliability and a high performance. This document provides the Tj evaluation results under two conditions by using different heat sinks. Please use the data as reference for NCSU03xx’s thermal design at your site. 2. Tj Calculation Tj can be obtained by the following formula: Tj = Ts + Rthj-s × PD Light Emitting Diode where, Tj: Junction Temperature [°C] Ts: Soldering Temperature [°C] Rthj-s: Thermal resistance between the LED die and the Ts measuring point [°C/W] * The Rthj-s of NCSU03xx is Typ:4.4 [°C/W] (Max:7.3 [°C/W]) PD: Input Power [W] TS Point 3. Tj Measurement Result Figure 1 Ts Measuring Point Ex.1 Aluminum Board IF(A) 0.5 0.7 TS (℃) 75 95 VF(V) 3.57 3.63 Tj (℃) 83 106 Ex.2 Aluminum Board + Heat Sink IF(A) 0.5 0.7 TS (℃) 54 66 VF(V) 3.62 3.70 Tj (℃) 62 77 Front Side Reverse Surface Figure 2 Aluminum Board Front Side Reverse Surface 4. Heat Dissipation Materials - Metal-based board; Aluminum, Dimension; 30mm×30mm×1.6mm Figure 3 Aluminum Board & Heat Sink - Heat Sink : 30mm×30mm×h=20mm, Depth: 4mm, Fin; 64 pcs. (Dimension of Fin; 1.4mm×2mm, Structure; 8×8) Note: Absolute Maximum Ratings Nichia specifies the absolute maximum ratings for NCSU03xx as IF=0.7A and Tjmax =130°C. We cannot assure the performance of the LEDs if they are used above the specified temperature and IF. Thank you very much for your cooperation. This sheet contains tentative information, we may change contents without notice. (SP-QR-C-2037A) Oct. 2, 2013