MP3305
36V, 1.3A, Step-up
White LED Driver
with High Frequency True PWM Dimming & Adjust OVP
MP3305 Rev. 1.0 www.MonolithicPower.com 1
4/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
The Future of Analog IC Technology
DESCRIPTION
The MP3305 is a monolithic step-up converter
designed for driving arrays of WLEDs from 5V
input or a single cell Lithium Ion battery. The
MP3305 uses current mode, fixed frequency
architecture to regulate the LED current, which is
measured through an external current sense
resistor. Its low 200mV feedback voltage reduces
power loss and improves efficiency.
The MP3305 features up to 50kHz true PWM
dimming, which allows the flexible control of the
backlighting luminance under wide range of the
ambient brightness, and also avoids the
possibility of PWM dimming audible noise.
The MP3305 is turned off if an over-voltage
condition is present due to an open circuit
condition. Use one external resistor voltage
divider to adjust OVP threshold. MP3305 also
includes under-voltage lockout, current limiting
and thermal overload protection preventing
damage in the event of an output overload.
The MP3305 is available in small 8-pin QFN
2x3mm package.
FEATURES
• Internal Power MOSFET
• Drives up to 10 Series White LEDs
• Up to 88% Efficiency
• PWM Dimming Frequency from 250Hz to
50kHz
• 2.2MHz Fixed Switching Frequency
• Adjustable Open Load Shutdown Threshold
(OVP)
• Low 200mV Feedback Voltage
• UVLO, Thermal Shutdown
• Internal 1.3A Current Limit
• Available in 2mm x 3mm QFN8 Package
APPLICATIONS
• LCD Panels
• Digital Picture Frames
• Handheld Computers and PDAs
• Digital Still Cameras
• Small LCD Displays
All MPS parts are lead-free and adhere to the RoHS directive. For MPS green
status, please visit MPS website under Quality Assurance. “Monolithic Powe
r
Systems”, “MPS”, and “The Future of Analog IC Technology” are Registered
Trademarks of Monolithic Power Systems, Inc.
TYPICAL APPLICATION
MP3305
VIN
5V
Enable/
Dimming
Control
LED1
LED2
LED3
R2 R1
RSET
LD
C1
C2
LED28
LED29
LED30
IN
EN
GND LED
ISETOVP
SW
String 1 String 10...
VIN vs. Efficiency
50
60
70
80
90
100
3 3.5 4 4.5 5 5.5 6 6.5
V
IN
(V)
EFFICIENCY (%)
MP3305 –36V, 1.3A, STEP-UP WHITE LED DRIVER WITH HIGH FREQUENCY TRUE PWM DIMMING & ADJUST OVP
MP3305 Rev. 1.0 www.MonolithicPower.com 2
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© 2013 MPS. All Rights Reserved.
ORDERING INFORMATION
Part Number* Package Top Marking Free Air Temperature (TA)
MP3305DD QFN8 (2mm x 3mm) 6E -40°C to +85°C
* For Tape & Reel, add suffix –Z (e.g. MP3305DD–Z).
For RoHS compliant packaging, add suffix –LF (e.g. MP3305DD–LF–Z)
PACKAGE REFERENCE
ABSOLUTE MAXIMUM RATINGS (1)
SW Pin, LED Pin...........................-0.5V to +40V
All Other Pins...............................-0.3V to +6.5V
Storage Temperature............... -55°C to +150°C
Continuous Power Dissipation (TA = +25°C) (2)
………………………………………………....1.9W
Recommended Operating Conditions (3)
IN Supply Voltage .................................3V to 6V
SW Pin................................................VIN to 36V
Operating Junct. Temp (TJ)...... -40°C to +125°C
Thermal Resistance (4) θJA θJC
QFN8 (2mm x 3mm) ...............65 ...... 13... °C/W
Notes:
1) Exceeding these ratings may damage the device.
2) The maximum allowable power dissipation is a function of the
maximum junction temperature TJ (MAX), the junction-to-
ambient thermal resistance θJA, and the ambient temperature
TA. The maximum allowable continuous power dissipation at
any ambient temperature is calculated by PD (MAX) = (TJ
(MAX)-TA)/θJA. Exceeding the maximum allowable powe
r
dissipation will cause excessive die temperature, and the
regulator will go into thermal shutdown. Internal thermal
shutdown circuitry protects the device from permanent
damage.
3) The device is not guaranteed to function outside of its
operating conditions.
4) Measured on JESD51-7, 4-layer PCB.
TOP VIEW
SW
PGND
VIN
OVP
1
2
3
4
GND
ISET
LED
EN
8
7
6
5
Exposed Pad
Connect to GND
MP3305 –36V, 1.3A, STEP-UP WHITE LED DRIVER WITH HIGH FREQUENCY TRUE PWM DIMMING & ADJUST OVP
MP3305 Rev. 1.0 www.MonolithicPower.com 3
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© 2013 MPS. All Rights Reserved.
ELECTRICAL CHARACTERISTICS
VIN = VEN = 5V, TA = +25°C, unless otherwise noted.
Parameters Symbol Condition Min Typ Max Units
Operating Input Voltage VIN 2.5 6 V
Supply Current (Shutdown) IIN_SD V
EN = 0V 1 2 µA
Supply Current (Quiescent) IIN_QS V
ISET = 0.3V 690 850 µA
Switching Frequency FSW 1.7 2.2 2.7 MHz
Maximum Duty Cycle DMAX V
ISET = 0V 90 %
Under Voltage Lockout
IN Under Voltage Lockout VUVLO V
IN Rising 2.25 2.45 V
Under Voltage Lockout
Hysteresis 92 mV
Open Lamp Shutdown
Threshold VOVP V
OV Rising 0.9 V
Enable
EN OFF Threshold VEN_LOW V
EN Falling 0.4 V
EN ON Threshold VEN_HIGH V
EN Rising 1.8 V
Disable Timer 5 ms
Minimum EN ON Pulse 5 µs
Feedback
ISET Voltage VISET V
EN > 2V 185 200 215 mV
ISET Input Bias Current VISET = 0.2V -600 -300 nA
Output Switch
SW On-Resistance RON 0.4 Ω
SW Current Limit Duty Cycle = 60% 1.33 A
Thermal Shutdown 150 °C
LED Switch (M2, refer block
diagram) On Resistance 0.8 Ω
MP3305 –36V, 1.3A, STEP-UP WHITE LED DRIVER WITH HIGH FREQUENCY TRUE PWM DIMMING & ADJUST OVP
MP3305 Rev. 1.0 www.MonolithicPower.com 4
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© 2013 MPS. All Rights Reserved.
PIN FUNCTIONS
QFN8
Pin # Name Pin Function
1 SW
Power Switch Output. SW is the drain of the internal MOSFET switch. Connect the power
inductor and output rectifier to SW. SW can swing between GND and 36V.
2,8
GND,
Exposed
Pad
Ground. Connect exposed pad to GND plane for proper thermal performance.
3 IN Input Supply Pin. Must be locally bypassed.
4 OVP
Open Load Protection Adjusting pin. Connect a resistor divider from output to this pin to
adjust the OVP threshold. When this pin voltage reaches the shutdown threshold 0.9V, the
switch will be turned off
5 EN
ON/OFF Control and Dimming Command Input. Holding EN pin low for more than 5ms will
turn the part off. To use PWM dimming, add a 250Hz to 50KHz square wave signal to this
pin.
6 LED
LED Current Input. This pin is the open-drain output of an internal dimming control switch.
Connect the LED cathode to this pin.
7 ISET
LED Current Set. This pin is the source output of an internal dimming control switch. The
MP3305 regulates the voltage across the current setting resistor. Tie a current setting
resistor from this pin to ground. The regulation voltage is 200mV.
MP3305 –36V, 1.3A, STEP-UP WHITE LED DRIVER WITH HIGH FREQUENCY TRUE PWM DIMMING & ADJUST OVP
MP3305 Rev. 1.0 www.MonolithicPower.com 5
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© 2013 MPS. All Rights Reserved.
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 5V, ILED = 200mA, 3WLEDs 10Strings, unless otherwise noted.
Open Load Protection
PWM Dimming
fPWM=50kHz, DPWM=50%
Steady State Operation
Enable Startup Enable Shutdown
I
INDUCTOR
500mA/div
FB
50mV/div
V
OUT
(AC)
100mV/div
SW
5V/div
I
LED
200mA/div
EN
5V/div
V
OUT
5V/div
SW
10V/div
I
LED
100mA/div
V
OUT
5V/div
SW
10V/div
I
LED
100mA/div
EN
5V/div
V
OUT
5V/div
SW
10V/div
I
LED
200mA/div
PWM
2V/div
V
OUT
10V/div
SW
10V/div
400ns/div
VIN vs. Efficiency
50
60
70
80
90
100
3 3.5 4 4.5 5 5.5 6 6.5
V
IN
(V)
EFFICIENCY (%)
PWM Dimming Duty vs.
WLED Current
0
20
40
60
80
100
120
140
160
180
200
020406080100
PWM DIMMING DUTY (%)
WLED CURRENT (MA)
50kHz
20kHz
250Hz
1kHz
MP3305 –36V, 1.3A, STEP-UP WHITE LED DRIVER WITH HIGH FREQUENCY TRUE PWM DIMMING & ADJUST OVP
MP3305 Rev. 1.0 www.MonolithicPower.com 6
4/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
OPERATION
The MP3305 uses a constant frequency, peak
current mode boost regulator architecture to
regulate the series string of white LEDs. The
operation of the MP3305 can be understood by
referring to the block diagram of Figure 1.
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 percent, 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 200mV 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
Enable
CONTROL
LOGIC
CURRENT
SENSE
AMPLIFIER
SW
M1
M2
PGND
OVP
0.9V
-
+
LED
ISET
ISET
EN
GND
2.2MHz
OSC
ENABLE &
DIMMING
CONTROL
-
+
-
+
+
-
+
Figure 1—Functional Block Diagram
MP3305 –36V, 1.3A, STEP-UP WHITE LED DRIVER WITH HIGH FREQUENCY TRUE PWM DIMMING & ADJUST OVP
MP3305 Rev. 1.0 www.MonolithicPower.com 7
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© 2013 MPS. All Rights Reserved.
APPLICATION INFORMATION
Enable/
Dimming
Control
MP3305
V
IN
5V MBR0520
C2
C1
IN
EN
GND LED
ISETOVP
SW
Figure 2—Circuit for Driving 10 Strings of 3 WLEDs
A typical application circuit can be seen in Figure
2. The 10 strings of 3 white LEDs can be driven
from a 5V 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 MP3305. The MP3305 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: ILED =200mV/R1.
Table 1 shows the selection of resistors for a
given LED current.
Table 1—ILED vs. R1
ILED (mA) R1 (Ω)
1 200
5 40
10 20
20 10
60 3.33
180 1.11
200 1
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 MP3305 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 adjusted OVP threshold
(+
OV
R2
V =0.9V(1 )
R3 ), the MP3305 will shut down.
The part will not switch again until the power is
recycled.
MP3305 –36V, 1.3A, STEP-UP WHITE LED DRIVER WITH HIGH FREQUENCY TRUE PWM DIMMING & ADJUST OVP
MP3305 Rev. 1.0 www.MonolithicPower.com 8
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© 2013 MPS. All Rights Reserved.
Layout Considerations
Careful attention must be paid to the PCB board
layout and components placement. Proper layout
of the high frequency switching path is critical to
prevent noise and electromagnetic interference
problems. The loop of MP3305 SW to GND pin,
output diode, and output capacitor is flowing with
high frequency ripple current, it must be as short
as possible. And connect the GND (2 pin) and
PGND (8 pin) together thru thermal pad, as
showed in Figure 3.
Figure 3—Layout consideration
The IN pin of the IC must be locally bypassed. A
RC filter is highly recommended for eliminating
the noise on IN pin. It could be implemented as
shown in Figure 4.
MP3305
SW
GND
IN
Input
Figure 4—Input Bias Filtering
MP3305 –36V, 1.3A, STEP-UP WHITE LED DRIVER WITH HIGH FREQUENCY TRUE PWM DIMMING & ADJUST OVP
MP3305 Rev. 1.0 www.MonolithicPower.com 9
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© 2013 MPS. All Rights Reserved.
TYPICAL APPLICATION CIRCUITS
MP3305
SW
OVP
IN
ISET
LED
PGNDGND
EN
LED+
LED-
C2
330nF
50V
D2
5.6V
7.5
ZENER
D1
B0540L1
10uH
Optional
Bias Circuit
GND
EN
VIN
3.3V -18V C1
R3
R4
10uF
25V
C3
0.1uF
50V
2
31
6
7
5
8
4
Figure 5 — Driving 27 WLEDs (9 WLEDs in Series and 3 Strings Paralleled) with 3.3V-18V Input Voltage
In order to improve the MOSFET on-resistance at low input voltage and make the chip compatible for
high input voltage, the additional bias circuit should be used.
MP3305
SWOVP
LED
IN
ISETPGNDGND
EN
GND
EN
LED+
LED-
VIN
4.5V-18V
C1
10uF
25V C4
330nF
50V
C3
0.1uF
25V
Q2
2N3904
D2
5.6V
ZENER
Required Bias Circuit
for High Input Voltage
L1 D1
10uH B0540
78
2
3
4
1
6
5
Figure 6 — Wide Input Voltage Step-up Converter for 27 WLEDs
( 9 WLEDs in Series and 3 Strings Paralleled )
MP3305 –36V, 1.3A, STEP-UP WHITE LED DRIVER WITH HIGH FREQUENCY TRUE PWM DIMMING & ADJUST OVP
MP3305 Rev. 1.0 www.MonolithicPower.com 10
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© 2013 MPS. All Rights Reserved.
TYPICAL APPLICATION CIRCUITS (continued)
MP3305
SW OVP
IN
LED
GND
ISETPGND
EN
C3
330nF
R1
R2
D1
B0540
L1
LED1
LED2
LED3
LED4
LED5
LED6
LED7
LED8
LED9
LED10
GND
EN
VIN
5V C1
16V
C2
16V
1
27
5
86
4
3
1%
R3
R4
Figure 7 — Driving 10 WLEDs in Series with 5V Input Voltage
MP3305 –36V, 1.3A, STEP-UP WHITE LED DRIVER WITH HIGH FREQUENCY TRUE PWM DIMMING & ADJUST OVP
NOTICE: The information in this document is subject to change without notice. Users should warrant and guarantee that third
party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not
assume any legal responsibility for any said applications.
MP3305 Rev. 1.0 www.MonolithicPower.com 11
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© 2013 MPS. All Rights Reserved.
PACKAGE INFORMATION
QFN8 (2mm x 3mm)
SIDE VIEW
TOP VIEW BOTTOM VIEW
2.90
3.10
1.90
2.10
0.00
0.05
PIN 1 ID
MARKING
1.70
0.50
0.25
RECOMMENDED LAND PATTERN
2.90
NOTE:
1) ALL DIMENSIONS ARE IN MILLIMETERS.
2) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH.
3) LEAD COPLANARITY SHALL BE 0.10 MILLIMETER MAX.
4) DRAWING CONFORMS TO JEDEC MO-229, VARIATION VCED-2.
5) DRAWING IS NOT TO SCALE.
1.60
0.70
PIN 1 ID OPTION B
R0.20 TYP.
DETAIL A
PIN 1 ID
INDEX AREA
1
8
5
4
1.65
1.85
1.50
1.70
0.50
BSC
0.18
0.30
PIN 1 ID
SEE DETAIL A
0.30
0.50
0.80
1.00
0.20 REF
PIN 1 ID OPTION A
0.30x45” TYP.
