ZXLD1374

60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST

LED DRIVER CONVERTER WITH AEC-Q100

ZXLD1374

Document number: DS35032 Rev. 2 - 2

27 of 37

www.diodes.com

March 2011

© Diodes Incorporated

A Product Line of

Diodes Incorporated

The device can be put in standby by taking the PWM pin to ground, or pulling it to a voltage below 0.4V with a suitable open

collector NPN or open drain NMOS transistor, for a time exceeding 15ms (nominal). In the shutdown state, most of the

circuitry inside the device is switched off and residual quiescent current will be typically 90µA. In particular, the Status pin

will go down to GND while the FLAG and REF pins will stay at their nominal values.

Fig 46. Stand-by state from PWM signal

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.

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

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

Figure 47. Thermal feedback network

For example,

1)

2)

TH1 = 10k

Ω at 25˚C and beta= 3500

TH1 = 3.3k

Ω at 70˚C

3)