MP3302 –40V, 1.3A, SINGLE-CELL STEP-UP WHITE LED DRIVER WITH SINGLE WIRE DIMMING CONTROL
MP3302 Rev. 0.98 www.MonolithicPower.com 8
5/5/2010 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
LED Current Programming
Applying a DC voltage between 0.7V and 1.4V
to EN pin programs a feedback voltage
between 0V and 200mV. Thus the analog
dimming of LED current can be achieved. The
DC dimming voltage must be locally bypassed
to prevent noise interfering with the feedback
reference level.
PWM Dimming
Apply a 200Hz to 1kHz square waveform to the
EN pin to implement PWM dimming of the
LEDs. The minimum recommended amplitude
of the PWM signal is 1.5V.
For high frequency PWM dimming (>1kHz), it is
also recommended that the dimming control be
implemented as shown in Figure 3. The cut off
frequency of the RC filter should be 10 times
lower than that of the input PWM signal. For
example, when the PWM frequency is 20kHz, a
20k resistor and 100nF capacitor can be used.
The DC voltage on EN pin is then equal to the
PWM high level voltage multiplies the PWM
duty
. The DC voltage from 0.7V to 1.4V
programs the output current from 0~100%.
PWM
MP3302
LED1
LED2
LED3
FB
EN
Figure 3—High Frequency PWM Dimming
Control
Open Load Protection
Open Load protection will shut off the MP3302
if the output voltage goes too high. In some
cases an LED may fail, this will result in the
feedback voltage always being zero. The part
will run at maximum duty cycle boosting the
output voltage higher and higher. If the output
ever exceeds 42V, the MP3302 will shut down.
The part will not switch again until the power is
recycled.
Layout Considerations
Careful attention must be paid to the PCB
board layout and components placement.
Proper layout of the high frequency switching
path is critical to prevent noise and
electromagnetic interference problems. The
current loop of IC, output diode, and output
capacitor should be as short as possible.
The IN pin of the IC must be locally bypassed.
A RC filter is highly recommended for
eliminating the noise on IN pin. It could be
implemented as shown in Figure 4.
MP3302
SW
GND
IN
Input
Figure 4—Input Bias Filtering
