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Application Note
Tj Control for Good Heat Dissipation in NCSU275 (U395)
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): 10.5°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 (℃)
41.3
48.6
59.8
VF(V)
3.6
3.7
4.0
Tj (℃)
60
76
102
Reverse
Side
Front Side
Picture 2 Copper Board
Example 2. Copper Board + Heat Sink C
IF(A)
0.5
0.7
1.0
TS (℃)
37.5
42.9
51.2
VF(V)
3.6
3.8
4.0
Tj (℃)
56
71
93
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-4388)
Sep. 30, 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-4388)
Sep. 30, 2014
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