Most high power LEDS require thermal management. Simple thermal control can be achieved by reducing the voltage on the ADJ pin by connecting a negative temperature coefficient thermistor to ground. A suitable value for a directly connected thermistor would be 1 meg ohm at 25 degrees centigrade. The thermistor forms a voltage divider with the internal 200 kilo ohm resistor. The thermistor must be mounted in close thermal contact with the LED. As the temperature increases in the LED, the thermistor resistance drops which reduces the current in the LED this in turn lowers the temperature of the LED. This approach is simple but does have some disadvantages. First the 1 meg ohm thermistor will reduce the LED current by approximately 20% at 25 degrees centegrade. To get the LED current back to full brightness Rsense will need to be reduced by 20%. Second, as temperature goes down the LED current will go up. It will not exceed 20% higher but this may not be desirable even at negative temperatures. Lastly, with this simple technique you cannot set when the thermal control starts to operate.