Application Note Tj Control for Good Heat Dissipation in NVSU333A (U405) with Water Cooling System 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 NVSU333A, to deliver high reliability/performance. This document shows the Tj evaluation results by demonstrating two heat dissipation conditions with a water cooling system. 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 Thermistor Tj: Junction Temperature Ts: Soldering Temperature (°C) Rthj-s: Thermal resistance (°C/W) from the die to the Ts measuring point * Rthj-s (NVSU333A): 2.08°C/W TS Point PD: Input Power (W) 3. Ts Measuring Point Cathode Mark Picture 1 Ts Measuring Point The thermocouple was solder-attached to the Ts measuring point for the evaluation. (Board Size: 60mm ˣ 60 mm ˣ 1mm) Anode Cathode Ts Point 4. Tj Evaluation Result Board IF (A) Thermistor(℃) TS (℃) VF (V) Tj (℃) Cu 3.5 25 34 3.85 62 5. Heat Dissipating Conditions Interface between Heat Sink and Board Input Current ［ A］ Temperature ［℃］ Water Flow ［ L/min.］ Cooling Heat Sink LED Pitch ［ mm］ Internal Circuit 3.5 18 2.5 Oxygen-free copper 60mm×60mm×10mm 8.2 9 LEDs connected in series Thermal Conductivity ［W/(m ・K)］ Material 0.9 Grease Note We specified the absolute maximum ratings for NVSU333A; IF=4.5A and Tjmax = 100°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-4619) Oct. 21, 2014