MP3205 MPS, MP3205 Datasheet - Page 4

• Manufacturer Part Number: MP3205
• Description: 1.3mhz Fixed Frequency 5 White Led Driver
• Manufacturer: MPS

APPLICATION INFORMATION
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.
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
V
overshoot on the output. The current limit is
increased by a fourth every 40μs giving a total
soft-start time of 120μs.
MP3205 Rev. 1.3
10/8/2007
IN
at startup and to also limit the amount of
(AC COUPLED)
V
Figure 3—Steady-State Operation
OUT
100mA/div.
50mV/div.
RIPPLE
5V/div.
V
A
V
IN
TM
SW
=3.6V, 3 LEDs, 20mA
I
L
1μF
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
2.5V to 6V
OFF ON
ceramic
V
IN
capacitor
Figure 2—Driving 3 White LEDs
MP3205_F03_WF01
MP3205 – 1.3 MHz FIXED FREQUENCY 5 WHITE LED DRIVER
© 2007 MPS. All Rights Reserved.
4
2
www.MonolithicPower.com
EN
GND
5
IN
MP3205
is
SW
FB
1
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.
Figure 5 shows the dependence on current limit
versus duty cycle.
CMDSH-3
3
Figure 5—Current Limit vs. Duty Cycle
LED1
LED2
LED3
100mA/div.
Figure 4—Startup Waveforms
5V/div.
5V/div.
V
500
400
300
200
100
V
OUT
V
EN
I
0
IN
IN
0
=3.6V, 3 LEDs, 20mA
MP3205_F02_AP_S01
20
DUTY CYCLE (%)
40
60
80
MP3205_F04_WF02
MP3205_F05
100
4