EV3205DJ-00A 데이터 시트보기 (PDF) - Monolithic Power Systems
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EV3205DJ-00A Datasheet PDF : 6 Pages
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TM
MP3205 – 1.3 MHz FIXED FREQUENCY 5 WHITE LED DRIVER
APPLICATION INFORMATION
VIN
2.5V to 6V
CMDSH-3
OFF ON
5
1
IN
SW
4
EN MP3205
2
GND
FB 3
LED1
LED2
LED3
Figure 2—Driving 3 White LEDs
MP3205_F02_AP_S01
COMPONENT SELECTION
A typical application circuit can be seen in Figure
2. The 3 white LEDs can be driven from a voltage
supply range of 2.5V to 6V at an output current of
20mA. A 0.22µF output capacitor is sufficient for
most applications but an output capacitor up to
1µF may be used. A 22µH inductor with low DCR
(Inductor resistance) is recommended to improve
efficiency. A 1µF ceramic capacitor is
recommended for the input capacitance in the
real system. Schottky diodes have fast recovery
and a low forward voltage and are recommended.
Schottky diodes rated with 100mA to 200mA
are sufficient for the MP3205. The switching
characteristics during normal operation can be
seen in Figure 3. The MP3205 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 current limit is
increased by a fourth every 40µs giving a total
soft-start time of 120µs.
Figure 4 shows the startup behavior of the
MP3205. 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.
VEN
5V/div.
VOUT
5V/div.
IIN
100mA/div.
MP3205_F04_WF02
Figure 4—Startup Waveforms
VIN=3.6V, 3 LEDs, 20mA
Figure 5 shows the dependence on current limit
versus duty cycle.
500
VSW
400
5V/div.
VOUT RIPPLE
300
(AC COUPLED)
50mV/div.
200
IL
100mA/div.
100
MP3205_F03_WF01
Figure 3—Steady-State Operation
VIN=3.6V, 3 LEDs, 20mA
0
0 20 40 60 80 100
DUTY CYCLE (%) MP3205_F05
Figure 5—Current Limit vs. Duty Cycle
MP3205 Rev. 1.3
www.MonolithicPower.com
4
7/13/2005
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© 2005 MPS. All Rights Reserved.
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