ZXLD1350Q Просмотр технического описания (PDF) - Diodes Incorporated.

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ZXLD1350Q

AUTOMOTIVE COMPLIANT 350mA BUCK LED DRIVER

Diodes Incorporated. 

ZXLD1350Q

Application Information (Cont.)

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:

VADJ

PWM

0V

GND

ADJ ZZXXLLDD11335500Q

GND

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:

PWM

GND

ADJ ZZXXLLD135500Q

GND

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:

MCU

10k

ADJ ZZXXLLDD11335050Q

GND

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.

ZXLD1350Q

Document number: DS37076 Rev. 2 - 2

11 of 21

www.diodes.com

September 2017

© Diodes Incorporated

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