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MP3204DJ-LF-Z

P1-P3P4-P6P7-P7
MP3204 – 6V, 1.3MHz WHITE LED DRIVER
MP3204 Rev. 1.4 www.MonolithicPower.com 4
10/8/2007 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
TM
APPLICATION INFORMATION
OFF ON
MP3204
V
IN
2.5V to 6V
LED1
LED2
LED3
CMDSH-3
IN
EN
5
3
4
61
2
GND
OV
FB
SW
Figure 2—Driving 3 White LEDs
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 of up to 1µF may be used.
A 22µH inductor with low DCR (inductor
resistance) is recommended for improved
efficiency. A 1µF ceramic capacitor is
recommended for the input capacitance in the
real system. Schottky diodes have fast recovery
times and a low forward voltage and are also
recommended. Schottky diodes with ratings of
100mA to 200mA are sufficient for use with the
MP3204. The switching characteristics during
normal operation can be seen in Figure 3. The
MP3204 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.
V
OUT
RIPPLE
(AC COUPLED)
50mV/div.
V
SW
5V/div.
I
L
100mA/div.
Figure 3—Steady-State Operation
(V
IN
=3.6V, 3 LEDs, 20mA)
MP3204 – 6V, 1.3MHz WHITE LED DRIVER
MP3204 Rev. 1.4 www.MonolithicPower.com 5
10/8/2007 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
TM
Figure 4 shows the startup behavior of the
MP3204. 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.
V
OUT
5V/div.
V
EN
5V/div.
I
IN
100mA/div.
Figure 4—Startup Waveforms
(V
IN
=3.6V, 3 LEDs, 20mA)
Figure 5 shows the dependence on current limit
versus duty cycle.
500
400
300
200
100
0
CURRENT LIMIT (mA)
0 20406080100
DUTY CYCLE (%)
Figure 5—Current Limit vs. Duty Cycle
Setting the LED Current
The LED current is controlled by the feedback
resistor, R1, as shown in Figure 2. The current
through the LEDs is equal to 104mV/R1. Table
1 shows the selection of resistors for a given
LED current.
Table 1—I
LED
vs. R1
I
LED
(mA) R1 (Ω)
1 104
5 20.8
10 10.4
15 6.93
20 5.2
Analog and Digital Dimming
There are three different ways to control
dimming for the MP3204 during normal
operation. The first way uses a DC voltage to
control the feedback voltage, which can be
seen in Figure 6. As the DC voltage increases,
current starts flowing down R1, R2 and R3. The
loop will continue to regulate the feedback
voltage to 104mV. Thus, the current has to
decrease through the LEDs by the same
amount of current as is being injected from the
DC voltage source. With a VDC from 0V to 2V,
the resistor values shown for R2 and R3 can
control the LED current from 0mA to 20mA.
MP3204
LED1
LED2
LED3
FB
3
V
DC
Figure 6—Dimming Control Using a DC
Voltage
MP3204 – 6V, 1.3MHz WHITE LED DRIVER
MP3204 Rev. 1.4 www.MonolithicPower.com 6
10/8/2007 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
TM
Other applications require the use of a logic
signal to execute the dimming. This can be
seen in Figure 7. The PWM signal is applied to
the EN pin of the MP3204. The LEDs will switch
between full load to complete shutoff. The
average current through the LEDs will increase
proportionally to the duty cycle of the PWM
signal. The signal used in Figure 7 should be
1KHz or below due to the soft-start function.
PWM
MP3204
LED1
LED2
LED3
FB
EN
34
Figure 7—PWM Dimming Control Using a
Logic Signal
If the PWM signal is above 1KHz, dimming can
be achieved by using the circuit shown in
Figure 8.
PWM
MP3204
LED1
LED2
LED3
FB
3
Figure 8—Dimming Control Using a Filtered
PWM Signal
Open Load Protection
Open Load protection will shutoff the MP3204 if
the output voltage goes too high when the OV
pin is tied to the output. In some cases an LED
may fail, which will result in the feedback
voltage always being zero. The part will run at
the maximum duty cycle, boosting the output
voltage higher and higher. By tying the OV pin
to the top of the LED string the MP3204 checks
the said condition and if the output ever
exceeds 28V the MP3204 will shutdown. The
part will not switch on again until the power is
recycled. Figure 9 shows the behavior of the
MP3204 into an open load.
V
EN
5V/div.
V
OV
10V/div.
V
SW
10V/div.
Figure 9—Startup Waveforms into an Open
Load (V
IN
=3.6V)
Layout Considerations
Careful attention must be paid to the PCB
board layout and component placement. Proper
layout of the high frequency switching path is
critical to prevent noise and electromagnetic
interference problems. Due to the high
frequency switching, the length and area of all
the traces connected to the switch node should
be minimized. Refer to the evaluation board
EV3204DJ-00A for a sample layout of
theBMP3204.
P1-P3P4-P6P7-P7

MP3204DJ-LF-Z

Mfr. #:
Buy MP3204DJ-LF-Z
Manufacturer:
Monolithic Power Systems (MPS)
Description:
LED Lighting Drivers 5 LED 2.5-6Vin Swtch Drvr w/Open protect
Lifecycle:
New from this manufacturer.
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