ZXLD1370EST16TC datasheet(26/36 Pages) DIODES

26 / 36 page

ZXLD1370

Document number: DS32165 Rev. 4 - 2

26 of 36

www.diodes.com

March 2011

A Product Line of

Diodes Incorporated

Applications Information (Continued)

TADJ pin - Thermal control of LED current

The ‘Thermal control’ circuit monitors the voltage on the TADJ pin and reduces output current if the voltage on this pin falls

below 625mV. An external NTC thermistor and resistor can therefore be connected as shown below to set the voltage on

the TADJ pin to 625mV at the required temperature threshold.

This will give 100% LED current below the threshold

temperature and a falling current above it as shown in the graph. The temperature threshold can be altered by adjusting the

value of Rth and/or the thermistor to suit the requirements of the chosen LED.

The Thermal Control feature can be disabled by connecting TADJ to REF.

Here is a simple procedure to design the thermal feedback circuit:

Select the temperature threshold Tthreshold at which the current must start to decrease

Select the Thermistor TH1 (both resistive value at 25˚C and beta)

Select the value of the resistor Rth as Rth = TH at Tthreshold

Figure 34. Thermal feedback network

For example,

Temperature threshold Tthreshold = 70˚C

TH1 = 10k

Ω at 25˚C and beta= 3500

TH = 3.3k

Ω @ 70˚C

Rth = TH at Tthreshold = 3.3kΩ

Over-Temperature Shutdown

The ZXLD1370 incorporates an over-temperature shutdown circuit to protect against damage caused by excessive die

temperature. A warning signal is generated on the STATUS output when die temperature exceeds 125°C nominal and the

output is disabled when die temperature exceeds 150°C nominal. Normal operation resumes when the device cools back

down to 125°C.

ZXLD1370EST16TC Datasheet(PDF) 26 Page - Diodes Incorporated