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MP3202DG-LF-P

P1-P3P4-P6P7-P9
MP3202 – 1.3A FIXED FREQUENCY WHITE LED DRIVER
MP3202 Rev. 0.91 www.MonolithicPower.com 4
9/21/2007 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
OPERATION
The MP3202 uses a constant frequency, peak
current mode boost regulator architecture to
regulate the strings of white LEDs. Refer to the
block diagram in Figure 1 for details.
At the start of each oscillator cycle the FET is
turned on through the control circuitry. To
prevent sub-harmonic oscillations at duty cycles
greater than 50%, a stabilizing ramp is added to
the output of the current sense amplifier and the
result is fed into the positive input of the PWM
comparator. When this voltage equals the
output voltage of the error amplifier the power
FET is turned off.
The voltage at the output of the error amplifier
is an amplified version of the difference
between the 104mV reference voltage and the
feedback voltage. In this way the peak current
level keeps the output in regulation.
If the feedback voltage starts to drop, the output
of the error amplifier increases. This results in
more current flowing through the power FET,
thus increasing the power delivered to the
output.
PWM
COMPARATOR
AMPLIFIER
CONTROL
LOGIC
CURRENT
SENSE
AMPLIFIER
SW
M1
GND
-
+
FB
1.3MHz
OSC
-
+
+
-
+
104mV
Figure 1—Functional Block Diagram
MP3202 – 1.3A FIXED FREQUENCY WHITE LED DRIVER
MP3202 Rev. 0.91 www.MonolithicPower.com 5
9/21/2007 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
APPLICATION INFORMATION
OFF ON
MP3202
V
IN
4V to 6V
MBR0520
9 Strings
Total
IN
EN
GND
OV
FB
SW
Figure 2—Circuit for Driving 27 WLEDs
A typical application circuit is provided in Figure
2. The 27 white LEDs can be driven from a
voltage supply range of 4V to 6V at a total
output current of 180mA. A 2.2µF output
capacitor is sufficient for most applications but
up to 1µF may be used. A 10µH inductor with
low DCR (inductor resistance) is recommended
to improve efficiency. A 4.7µF ceramic
capacitor is recommended for the input
capacitance in the real system. Schottky diodes
with fast recovery and a low forward voltage are
recommended. Schottky diodes with a 500mA
rating are sufficient for the MP3202. The
switching characteristics during normal
operation can be seen in Figure 3. The MP3202
has internal soft-start to limit the amount of
current through the IN pin 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
SW
5V/div.
V
OUT AC
200mV/div.
I
L
500mA/div.
400ns/div.
Steady State Operation
V
IN
= 5V, 27 LEDS, 180mA
Figure 3—Steady State Operation
Figure 4 shows the startup behavior of the
MP3202. The ramped voltage 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.
MP3202 – 1.3A FIXED FREQUENCY WHITE LED DRIVER
MP3202 Rev. 0.91 www.MonolithicPower.com 6
9/21/2007 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
V
EN
5V/div.
V
OUT
5V/div.
I
OUT
200mA/div.
I
L
500mA/div.
Startup Waveforms
V
IN
= 5V, 27 LEDs, 180mA
Figure 4—Startup Waveforms
Figure 5 shows the dependence on current limit
versus duty cycle.
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
CURRENT LIMIT (A)
0 20406080100
DUTY CYCLE (%)
Figure 5—Current Limit vs. Duty Cycle
Setting the LED Current
The LED current is controlled by the feedback
resistors R1 and R2, as shown in Figure 2. The
current through the LEDs is given by the
equation:
2R1R
2R1R
mV104I
LED
×
+
×=
Table 1 shows the selection of resistors for a
given LED current.
Table 1—I
LED
vs. R1
I
LED
(mA) R1 (Ω) R2 (Ω)
10 10.4 N/A
50 2.08 N/A
100 1.04 N/A
150 1.5 1.3
180 1.2 1.1
Analog and Digital Dimming
There are three methods to control dimming for
the MP3202 during normal operation. The first
method uses DC voltage to control the
feedback voltage. This is shown 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 V
DC
from 0V to 2V, the resistor values shown for R2
and R3 can control the LED current from 0mA
to 20mA.
MP3202
LED1
LED2
LED3
FB
V
DC
Figure 6—Dimming Control Using a DC
Voltage
P1-P3P4-P6P7-P9

MP3202DG-LF-P

Mfr. #:
Buy MP3202DG-LF-P
Manufacturer:
Monolithic Power Systems (MPS)
Description:
LED Lighting Drivers 39 WLED, 1.3MHz Boost Driver
Lifecycle:
New from this manufacturer.
Delivery:
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