MP3301—1.3MHZ, 700MA, FIXED-FREQUENCY, STEP-UP DRIVER FOR WHITE LEDS
MP3301 Rev. 1.01 www.MonolithicPower.com 8
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LED Current Programming
Applying a DC voltage between 0.7V and 1.4V
to EN pin programs a feedback voltage
between 0V and 200mV for analog dimming of
LED current. Locally bypass the DC dimming
voltage to limit noise on the feedback reference.
PWM Dimming
Apply a 200Hz-to-1kHz square waveform to the
EN pin to implement PWM dimming. Use a
PWM amplitude of at least 1.5V.
For high-frequency PWM dimming (>1kHz),
implement the dimming control shown in Figure
3. Select the RC filter’s cut-off frequency
≤
. For example, for a PWM frequency of
20kHz, use a 20kΩ resistor and 100nF
capacitor. Then
Where V
EN
is the EN pin’s DC voltage V
PWM_high
is the PWM high level voltage, and D
PWM
is the
PWM duty cycle. A DC voltage from 0.7V to
1.4V programs the output current from 0% to
100%.
Figure 3: Control Circuit for High-Frequency
PWM Dimming
Open-Load Protection
Open-load protection shuts off the MP3301 if
the output voltage goes too high. In cases
where an LED may fail, this results in a zero
feedback voltage. The part runs at the
maximum duty cycle to continue increasing the
output voltage. If the output exceeds 42V, the
MP3301 will shut down. The part will not switch
on again until the device undergoes a power
cycle.
Layout Considerations
PCB layout requires care to prevent noise and
electromagnetic interference from the high-
frequency switching paths. Make the current
loop from the IC, output diode, and the output
capacitor as short as possible.
Locally bypass the IN pin, and use an RC filter
when possible to eliminate noise on the IN pin.
See Figure 4 for an implementation example.
Figure 4: Input Bias Filtering
