MP3304 MPS, MP3304 Datasheet - Page 7

• Manufacturer Part Number: MP3304
• Description: The Future Of Analog Ic Technology
• Manufacturer: MPS

APPLICATION INFORMATION
A typical application circuit can be seen in Figure
2. The 10 strings of 3 white LEDs can be driven
from a 5V voltage at an output current of 200mA.
A 2.2µF output capacitor is sufficient for most
applications. A 2.2µH inductor with low DCR
(Inductor DC resistance) is recommended to
improve efficiency. A 10µF ceramic capacitor is
recommended for the input capacitance in the
real system. Schottky diodes have fast recovery
and a low forward voltage are recommended.
Schottky diodes rated with 500mA are sufficient
for the MP3304. The MP3304 has internal soft-
start to limit the amount of current through VIN at
startup and to also limit the amount of overshoot
on the output.
The ramped voltage that is added to the current
sense amplifier reduces the current output as the
duty cycle increases. As more LEDs are added,
the output voltage rises but the current that can
be delivered to the load is reduced as well.
Setting the LED Current
The LED current is controlled by the current
setting resistor, R1. The current through the
LEDs is given by: I
Table 1 shows the selection of resistors for a
given LED current.
MP3304 Rev. 0.91
4/19/2010
MP3304 –36V, 1.3A, STEP-UP WHITE LED DRIVER WITH HIGH FREQUENCY TRUE PWM DIMMING
LED
= 200mV/R1.
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
Dimming
Enable/
Control
Figure 2—Circuit for Driving 10 Strings of 3 WLEDs
V
5V
IN
EN
GND
IN
© 2010 MPS. All Rights Reserved.
MP3304
ISET
www.MonolithicPower.com
L
LED
SW
MBR0520
D1
PWM Dimming
Apply a 250Hz to 50kHz square waveform to the
EN pin to implement PWM dimming of the LEDs.
The minimum recommended amplitude of the
PWM signal is 2V.
Open Load Protection
Open Load protection will shut off the MP3304 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 voltage ever
exceeds the open load protection threshold
voltage, the MP3304 will shut down. The part will
not switch again until the power is recycled. For
MP3304A, MP3304B, and MP3304C, the open
load protection threshold voltages are 38V, 26V,
and 20V respectively.
I
LED
180
200
10
20
60
1
5
(mA)
Table 1—I
LED
vs. R1 R
R1 (Ω)
3.33
1.11
200
40
20
10
1
SET
7