Diodes ZXLD1360 - Manual (Page 14)

ZXLD1360
ZXLD1360
Document number: DS33471 Rev. 4 - 2
14 of 25
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March 2011
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Application Information (cont.)
Directly driving ADJ input
A Pulse Width Modulated (PWM) signal with duty cycle D
PWM
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
S
:
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:
If the NMOS transistor within the microcontroller has high Drain / Source capacitance, this arrangement can inject a negative
spike into ADJ input of the 1360 and cause erratic operation but the addition of a Schottky clamp diode (cathode to ADJ) to
ground and inclusion of a series resistor (10k) 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.
PWM
GND
0V
V
ADJ
GND
ZXLD1360 ADJ
PWM
GND
ZXLD1360 ADJ
GND
GND
ZXLD1360 ADJ
MCU
10k