ZXLD1366

ZXLD1366

Document number: DS31992 Rev. 7 - 2

18 of 30

www.diodes.com

May 2012

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A Product Line of

Diodes Incorporated

Driving the ADJ Input via Open Collector Transistor

The recommended method of driving the ADJ pin and controlling the amplitude of the PWM waveform is to use a small NPN switching

transistor as shown below:

This scheme uses the 50k resistor between the ADJ pin and the internal voltage reference as a pull-up resistor for the external transistor.

Driving the ADJ Input from a Microcontroller

Another possibility is to drive the device from the open drain output of a microcontroller. The diagram below shows one method of doing this:

If the NMOS transistor within the microcontroller has high Gate / Drain capacitance, this arrangement can inject a negative spike into ADJ

input of the ZXLD1366 and cause erratic operation but the addition of a Schottky clamp diode (eg Diodes Inc. SD103CWS) to ground and

inclusion of a series resistor (3.3k) will prevent this. See the section on PWM dimming for more details of the various modes of control using

high frequency and low frequency PWM signals.

Shutdown Mode

Taking the ADJ pin to a voltage below 0.2V for more than approximately 100

μs will turn off the output and supply current to a low standby

level of 65

μA nominal.

average value. (See page 18 graphs for details).

PWM

GND

ZXLD1366

ADJ

GND

GND

ZXLD1366

ADJ

MCU

3.3k