Application Note Tj Control for Good Heat Dissipation in NCSU275 (U365) 1. Objective The LEDs’ light output can be affected by the heat generated from the LEDs/LED-assembled products. Also, the reliability performance can be seriously degraded, if the LEDs are operated over the absolute maximum rated junction temperature (Tj). It is critical to design the heat dissipation performance not to exceed the Tjmax for NCSU275, to deliver high reliability/performance. This document shows the Tj evaluation results by demonstrating two heat dissipation conditions. Please use the data for reference to your thermal design. Light Emitting Diode 2. Tj Calculation Tj can be calculated by the following formula: Tj = Ts + Rthj-s × PD Tj: Junction Temperature Ts: Soldering Temperature (°C) Rthj-s: Thermal resistance (°C/W) from the die to the Ts measuring point TS Point * Rthj-s (NCSU275): 16.4°C/W PD: Input Power (W) Picture 1 Ts Measuring Point The thermocouple was solder-attached to the Ts measuring point for the evaluation. 3. Ts Measuring Point 4. Tj Evaluation Result Example 1. Copper Board + Heat Sink B IF(A) 0.5 0.7 1.0 TS (℃) 42.9 50.2 61.6 VF(V) 3.6 3.8 4.0 Tj (℃) 72 94 127 Reverse Side Front Side Picture 2 Copper Board Example 2. Copper Board + Heat Sink C IF(A) 0.5 0.7 1.0 TS (℃) 39.6 45.6 54.7 VF(V) 3.7 3.8 4.0 Tj (℃) 70 89 120 HS-B HS-C Front Side HS-B HS-C Reverse Side Picture 3 Copper Board + Heat Sink This sheet contains tentative information; we may change the contents without notice. (SP-QR-C-4196A) Sep. 29, 2014 Application Note 5. Heat Dissipating Materials Metal-based Board: Copper, 30mm×30mm×1.7mm Heat Sink B: 50mm×38mm×25mm (H), Base Thickness: 5 mm, Fin: 8 pcs.(1mm×38mm, Array: 1×8) Heat Sink C: 54mm×54mm×35mm (H), Base Thickness: 4mm, Fin=64 pcs.(0.8mm×9mm, Array: 5×13） Light Emitting Diode Note We specified the absolute maximum ratings for NCSU275; IF= 0.7A and Tjmax = 130°C. We cannot guarantee the usage over these ratings. We appreciate your understanding and cooperation. This sheet contains tentative information; we may change the contents without notice. (SP-QR-C-4196A) Sep. 29, 2014