ZXLD1370Q

Document number: DS37117 Rev. 4 - 2

28 of 39

www.diodes.com

February 2018

© Diodes Incorporated

ZXLD1370Q

Thermal Control of LED Current

For thermal control of the LEDs, the ZXLD1370Q 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

LED.

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

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)

85

˚C

70

˚C

100%

10%

Thermal network response in Buck configuration with:

Rth = 1.8k

Ω and TH1=10kΩ (beta =3900)

REF

TADJ

Rth

TH1

Figure 34 Thermal Feedback Network





















T

e

R

R

R

1

T

1

B

R

T

Where:

B is the “beta” value of the thermistor.

For example,

(1)

(2)

TH1 = 10k

(3)

Ω

Overtemperature Shutdown

The ZXLD1370Q incorporates an overtemperature 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.