ZXLD1366_10 DIODES [Diodes Incorporated], ZXLD1366_10 Datasheet - Page 19

• Manufacturer Part Number: ZXLD1366_10
• Description: HIGH ACCURACY 1A, 60V LED DRIVER WITH INTERNAL SWITCH
• Manufacturer: DIODES [Diodes Incorporated]

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 R
V
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.
ZXLD1366
Document number: DS31992 Rev. 5 - 2
0V
ADJ
MCU
PWM
GND
GND
PWM
3.3k
ADJ
ADJ
ADJ
ZXLD1366
ZXLD1366
ZXLD1366
GND
GND
GND
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ZXLD1366
June 2010