ZXLD1356_10 DIODES [Diodes Incorporated], ZXLD1356_10 Datasheet - Page 19

• Manufacturer Part Number: ZXLD1356_10
• Description: 60V 550mA LED DRIVER with AEC-Q100
• Manufacturer: DIODES [Diodes Incorporated]

Application Information
Output Current Adjustment by PWM Control
Directly driving ADJ input
A Pulse Width Modulated (PWM) signal with duty cycle D
current to a value above or below the nominal average value set by resistor R
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 eg MMBT3904.
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 ZXLD1356 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.
ZXLD1356
Document number: DS33470 Rev. 3 - 2
V
ADJ
0V
MCU
PWM
GND
PWM
GND
3.3k
ADJ
ADJ
(Continued)
ADJ
ZXLD1356
GND
ZXLD1356
ZXLD1356
GND
GND
www.diodes.com
PWM
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can be applied to the ADJ pin, as shown below, to adjust the output
S
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ZXLD1356
December 2010