ZXLD1370

ZXLD1370

Document number: DS32165 Rev. 4 - 2

26 of 36

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March 2011

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

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.

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

1)

2)

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

3)

Figure 34. Thermal feedback network

For example,

1)

2)

TH1 = 10k

Ω at 25˚C and beta= 3500

TH = 3.3k

Ω @ 70˚C

3)

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.