ZXLD1350

30V 350mA LED DRIVER with AEC-Q100

ZXLD1350

Document number: DS33468 Rev. 8 - 2

13 of 22

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March 2011

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Application Information (Continued)

Output Current Adjustment by PWM Control

Directly driving ADJ input

A Pulse Width Modulated (PWM) signal with duty cycle DPWM can be applied to the ADJ pin, as shown below, to adjust the

output current to a value above or below the nominal average value set by resistor RS:

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 200k 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:

The diode and resistor suppress possible high amplitude negative spikes on the ADJ input resulting from the drain-source

capacitance of the FET. Negative spikes at the input to the device should be avoided as they may cause errors in output

current, or erratic device operation.

PWM dimming can be further split into high frequency and low frequency PWM dimming and how the device responds to

these.

VADJ

GND

ADJ

ZXLD1350

GND

0V

PWM

ADJ

ZXLD1350

GND

GND

PWM

ZXLD1350

GND

ADJ

10k

MCU