MP3308
Step-up White LED Driver
with Dual PWM Dimming Input Control
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP3308 is a monolithic step-up converter
designed to drive arrays of white LEDs from a
3.3V input or a single-cell lithium-ion battery.
The MP3308 uses fixed-frequency currentmode 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.
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•
•
•
•
The MP3308 features dual PWM-dimming input
control and true PWM dimming—this control
allows for a wide luminescent range that makes
the display readable under a variety of ambient
light conditions with minimal PWM dimming
noise.
Internal Power MOSFET
Drives Up to 10 White LEDs in Series
2.2MHz Fixed Switching Frequency
Up to 88% Efficiency
Dual PWM-Dimming Input Control
Internal 1.3A Current Limit
±3% True PWM Dimming Duty Accuracy
Adjustable Over-Voltage Protection
Threshold
Low 200mV Feedback Voltage
Under-Voltage Lockout, Short-Circuit
Protection, Thermal Shutdown
Available in 3mmx4mm QFN14 Package
•
•
•
APPLICATIONS
The MP3308 includes over-voltage protection,
short-circuit protection, under-voltage lockout,
current limiting, and thermal overload protection.
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The MP3308 is available in small 3mmx4mm
14-pin QFN package.
Small LCD Panels
Digital Picture Frames
Smartphones
Portable Media Players
Digital Cameras
All MPS parts are lead-free and adhere to the RoHS directive. For MPS green
status, please visit MPS website under Products, Quality Assurance page.
“MPS” and “The Future of Analog IC Technology” are registered trademarks of
Monolithic Power Systems, Inc.
TYPICAL APPLICATION
L
D
VOUT
VIN
CIN
COUT
IN
Enable
SW
EN
PWMIA
PWMIB
PWMOA
LED
MP3308
ISET
R ISET
PWMOB
COA
COB
GND
CFSET
MP3308 Rev. 1.02
7/19/2012
ROVP1
OVP
FSET
R OVP2
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© 2012 MPS. All Rights Reserved.
1
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
ORDERING INFORMATION
Part Number*
MP3308DL
Package
QFN14 (3x4mm)
Top Marking
3308
For Tape & Reel, add suffix –Z (e.g. MP3308DL-Z).
For RoHS, compliant packaging, add suffix –LF (e.g. MP3308DL–LF–Z).
PACKAGE REFERENCE
TOP VIEW
PIN 1 ID
1
14
2
13
3
12
4
11
5
10
6
9
7
8
EXPOSED PAD
ON BACKSIDE
CONNECT TO GND
QFN14 (3x4mm)
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
(2)
Continuous Power Dissipation (TA = 25°C)
………………………………………………....2.6W
Recommended Operating Conditions
(3)
Supply Voltage (VIN)..............................3V to 6V
SW Pin ................................................VIN to 36V
Operating Junction Temp. (TJ). -40°C to +125°C
MP3308 Rev. 1.02
7/19/2012
Thermal Resistance
(4)
θJA
θJC
QFN14 (3x4mm) .....................48 ...... 10 ... °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-toambient 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 power
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.
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© 2012 MPS. All Rights Reserved.
2
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
ELECTRICAL CHARACTERISTICS
VIN = VEN = 5V, TA = 25°C, unless otherwise noted.
Parameters
Symbol
Operating Input Voltage
VIN
Supply Current (Shutdown)
IIN_SD
Supply Current (Quiescent)
IIN_QS
Switching Frequency
fSW
Maximum Duty Cycle
DMAX
Under Voltage Lockout
VIN Under Voltage Lockout
VUVLO
Under Voltage Lockout Hysteresis
Over-Voltage Protection Threshold
VOVP
Enable and Dimming
EN/PWMIX OFF Threshold
VLOGIC_LOW
EN/PWMIX ON Threshold
VLOGIC_HIGH
True PWM Dimming Duty Accuracy
∆DDPWM
Feedback
ISET Voltage
VISET
ISET Input Bias Current
Output Switch
SW On-Resistance
RON
SW Current Limit
Thermal Shutdown
LED Switch ON-Resistance (M2 in
the functional block diagram)
MP3308 Rev. 1.02
7/19/2012
Condition
Min
Typ
2.5
VEN = 0V
VISET = 0.3V
VISET = 0V
1.7
90
VIN Rising
2.1
30
0.9
VOUT Rising
VEN Falling
VEN Rising
D_PWMIA=D_PWMIB=70%
0.4
VEN > 2V
VISET = 0.2V
185
-600
Duty Cycle = 60%
25
860
2.2
Max
Units
6
30
V
µA
µA
MHz
%
2.7
2.3
1.8
±3
200
-300
215
V
mV
V
V
V
%
mV
nA
0.4
1.33
150
Ω
A
°C
0.8
Ω
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© 2012 MPS. All Rights Reserved.
3
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
PIN FUNCTIONS
Pin #
Name
1
SW
2
3
4
5
6
7
8
9
10,14
11
12
13
Description
Power Switch Output. Drain of the internal MOSFET switch. Connect to the power
inductor and the output rectifier. SW can swing between GND and 40V.
PGND,
Power Ground. Connect exposed pad to GND plane for proper thermal performance.
Exposed Pad
IN
Input Supply Pin. Locally bypassed.
PWM Input A. Apply one PWM signal on this pin for brightness control. This signal is
PWMIA
uniform and filtered at PWMOA pin.
PWM Input B. Apply the other PWM signal on this pin for brightness control. This signal
PWMIB
is uniform and filtered at PWMOB pin.
EN
ON/OFF Control. Hold EN pin low to turn off part, high to turn of part.
PWM Dimming Frequency Programmer. Connect a capacitor from this pin to GND to set
FSET
the PWM-dimming frequency as the formula, FPWM(Hz) = 16176 / CFSET(nF)
PWMOB
PWM Filtered Output B. Connect a capacitor from this pin to GND.
PWMOA
PWM Filtered Output A. Connect a capacitor from this pin to GND.
GND
Ground.
Over-Voltage Protection. Connect a resistor divider from output to this pin to adjust the
OVP
OVP threshold. When this pin voltage reaches the shutdown threshold 0.9V, the switch
turns off.
LED Current Input. Open-drain output of an internal dimming control switch. Connect the
LED
LED cathode to this pin.
LED Current Set. This pin is the source output of an internal dimming control switch. The
ISET
MP3308 regulates the voltage across the current setting resistor. Tie a current-setting
resistor from this pin to ground. Regulates the voltage to 200mV.
MP3308 Rev. 1.02
7/19/2012
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© 2012 MPS. All Rights Reserved.
4
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
TYPICAL CHARACTERISTICS
V(Iset) vs. Temperature
V(OVP) vs. Temperature
204.000
0.893
203.000
0.890
202.000
0.887
201.000
0.884
200.000
0.881
199.000
0.878
198.000
-50
900
0
50
100
150
Quiescent Current vs.
Temperature
0.875
-50
2.5
880
2.4
870
2.35
860
2.3
850
2.25
840
2.2
830
2.15
820
2.1
810
2.05
MP3308 Rev. 1.02
7/19/2012
50
100
150
Operation Frequency vs.
Temperature
2.45
890
800
-50
0
0
50
100
150
2
-50
0
50
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© 2012 MPS. All Rights Reserved.
100
150
5
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
TYPICAL PERFORMANCE CHARACTERISTICS
VIN =5V, 3 LEDs in series, 9 strings parallel, 120mA/string, unless otherwise noted.
PWMIA Dimming Duty vs.
WLED Current
180
180
160
160
140
140
120
100
80
60
40
20
3 3.5
4
4.5
5
5.5
6
120
100
80
60
40
20
6.5
VIN (V)
180
PWMIB Dimming Duty vs.
WLED Current
LED CURRENT (mA)
EFFICIENCY
LED CURRENT (mA)
Efficiency vs. VIN
PWMIA DUTY CYCLE
PWMIB DUTY CYCLE
Steady State Operation
PWMIA*DPWMIB vs.
WLED Current
VIN Power On
160
140
VSW
5V/div.
VSW
5V/div.
120
100
VOUT
5V/div.
80
VOUT
5V/div.
VIN
5V/div.
IL
500mA/div.
60
40
20
VIN
5V/div.
WLED Current
100mA/div.
PWMIA/B DUTY CYCLE
VIN Shut Down
EN Power On
VSW
5V/div.
VSW
5V/div.
VOUT
5V/div.
VIN
5V/div.
VOUT
5V/div.
VEN
5V/div.
WLED Current
100mA/div.
MP3308 Rev. 1.02
7/19/2012
WLED Current
100mA/div.
EN Shut Down
VSW
5V/div.
VOUT
5V/div.
VEN
5V/div.
WLED Current
100mA/div.
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© 2012 MPS. All Rights Reserved.
6
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Open Load Protection
Short Protection
VSW
10V/div.
VSW
5V/div.
PWMib
5V/div.
PWMia
5V/div.
WLED Current
100mA/div.
MP3308 Rev. 1.02
7/19/2012
VSW
5V/div.
VOUT
5V/div.
WLED Current
200mA/div.
VOUT
5V/div.
VLED
5V/div.
IOUT
1A/div.
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© 2012 MPS. All Rights Reserved.
7
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
FUNCTIONAL BLOCK DIAGRAM
POWER
Regulator
FOR
BLOCKS ERROR
PWM
AMPLIFIER
COMPARATOR
ISET
LED
M2
ISET
ENABLE&
DIMMING
GENERATOR
EN
PWMIA
Dual PWM
Dimming Control
ENABLE
FOR
BLOCKS
IN
Control
logic
OSC
M1
CURRENT
SENSE
AMPLIFIER
SW
GND
OVP
PWMIB
0.9V
OVP
COMPARATOR
PWMOA
PWMOB
FSET
Figure 1—Functional Block Diagram
MP3308 Rev. 1.02
7/19/2012
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© 2012 MPS. All Rights Reserved.
8
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
OPERATION
The MP3308 uses a constant-frequency peakcurrent–mode boost-regulator architecture to
regulate multiple strings of white LEDs connected
in series.
External capacitors on the PWMOA and the
PWMOB pins smooth the PWM signals to
provide DC signals by selecting the proper time
constant.
At the start of each oscillator cycle, the control
circuitry turns on the MOSFET. A stabilizing ramp
at the output of the current sense amplifier
prevents sub-harmonic oscillations at duty cycles
greater than 50 percent—this output feeds into
the positive input of the PWM comparator. When
this voltage equals the output voltage of the error
amplifier the power MOSFET turns off.
MP3308 provides over-voltage protection, which
will shut off the MP3308 if the output voltage
goes too high. OVP pin senses the output
voltage through the tap of a resistor divider
between VOUT and GND. In the case of an LED
failure, the feedback voltage goes to zero and the
part will run at maximum duty cycle. The output
voltage then rises and triggers OVP if the OVP
pin exceeds 1.23V.
The error amplifier compares the difference
between the 200mV reference voltage and the
feedback voltage. If the feedback voltage drops,
the output of the error amplifier increases,
resulting in more current flowing through the
power MOSFET and increasing the power
delivered to the output, thus regulating the output.
MP3308 also provides short-circuit protection in
cases where individual LEDs on a string or a
whole LED string shorts: This condition causes
the ISET pin to pull high. If the voltage exceeds
0.4V for more than 240µs, MP3308 will shutdown.
Dual PWM dimming can adjust LED brightness.
True PWM dimming allows for flexible control of
the backlighting luminance to improve visibility for
a wide range of ambient brightness. A capacitor
on the FSET pin sets the PWM dimming
frequency with a duty cycle of:
DPWMIA × DPWMIB
Where DPWMIA is the duty cycle on the PWMIA pin,
and DPWMIB is the duty cycle on the PWMIB pin.
MP3308 Rev. 1.02
7/19/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
9
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
APPLICATION INFORMATION
L1
C1 C2
D1
VIN
C3
B0530
JP1
U1
R5
Bias
100
1
C4
0.1
2
3
R6
PWMA
PWMB
EN
4
10k
R7
5
10k
R8
6
MP3308
SW
GND
PGND
ISET
IN
LED
PWMIA
OVP
PWMIB
GND
EN
PWMOA
FSET
PWMOB
14
R1
1
R2
NS
C5
NC
LED+
R3
160k
13
C10
33nF
LED-
12
11
C6
NS
10
R4
10k
9
10k
R9
100k
R10
100k
R11
100k
C7
10nF
7
8
C8
68nF
C9
68nF
Figure 2—Typical Application Driving 9 Strings of 3 WLEDs
Figure 2 shows a typical application circuit that
can drive up to nine strings of three white LEDs
with an output of 9V/180mA. A 4.7µF output
capacitor is sufficient for most applications. A
3.3µH inductor with low DC inductor resistance
(DCR) will improve efficiency. Two 4.7μF ceramic
capacitors provide sufficient input decoupling.
Use Schottky diodes with fast recovery for high
frequencies, and rated for a 500mA peak
inductor current. An internal soft-start limits IIN at
startup and IOUT overshoot.
The ramped voltage added to the current sense
amplifier reduces the maximum output current as
the duty cycle increases. As more LEDs are
added, the output voltage rises but the maximum
current delivered to the load falls as well.
Setting the LED Current
The resistor R1 sets the LED current, where the
current value is given by:
ILED =
200mV
R1
Table 1 pairs resistor values with an LED current.
Table 1—ILED vs. R1
ILED (mA)
1
5
10
20
60
180
200
R1 (Ω)
200
40
20
10
3.33
1.11
1
PWM Dimming
PWM dimming requires the application of square
waves to both the PWMIA and the PWMIB pins.
A capacitor on the FSET pin sets the PWM
dimming frequency according to the equation:
FPWM(Hz) = 16176 / CFSET(nF),
For CFSET=10nF, the FPWM is set to 1.6kHz.
The recommended FPWM range is 50Hz to 50kHz.
The minimum recommended amplitude of the
PWM signal is 2V.
External capacitors on both PWMOA and
PWMOB, together with internal 100kΩ resistors
filter the square waveform to provide a DC value.
The time constant should be ten times greater
than a PWM waveform cycle:
RC > 10 ⋅ TPWM
MP3308 Rev. 1.02
7/19/2012
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© 2012 MPS. All Rights Reserved.
10
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
Selecting the Inductor
The inductor forces a higher output voltage
driven from a lower input voltage. A larger
inductor value results in less ripple current, a
lower peak inductor current, and reduces stress
on the internal N-Channel MOSFET. However,
larger-value inductor has a larger physical
footprint, higher series resistance, and lower
saturation current.
Choose an inductor that does not saturate under
the worst-case load conditions. Calculate the
required inductance value using the following
equations:
L≥
Layout Considerations
Layout requires special consideration to avoid
electromagnetic interference from the highfrequency switching path. The high-frequency
ripper current in the loop from the SW pin,
through the output diode, and output capacitor to
GND requires a connection loop that is as short
as possible.
The IN pin must be locally bypassed, with a
highly-recommended RC filter to eliminate noise.
See Figure 3 for an example of this circuit.
B0530
JP1
Bias
VIN
VOUT
D1
VIN
η × VOUT × D × (1− D)2
2 × fSW × ILOAD
D = 1−
L1
C1 C2
R5
100
U1
1
C4
0.1
2
3
Where VIN and VOUT are the input and output
voltages, fSW is the switching frequency, ILOAD is
the LED load current, and η is the efficiency.
MP3308
SW
GND
PGND
ISET
IN
LED
14
13
12
Figure 3—Input Bias Filtering
Over-Voltage Protection
Open Load protection will shut off the MP3308 if
the output voltage reaches over-voltage
protection (OVP) threshold. LED failures will
result in the feedback voltage falling to zero,
which will cause the part to run at maximum duty
cycle and boost the output voltage. If the output
voltage exceeds the adjusted OVP threshold:
VOV =0.9V(1 +
R2
R3
),
The MP3308 will shut down and will not remain
off until the power cycles.
MP3308 Rev. 1.02
7/19/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
11
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
C1 C2
L1
LED+
TYPICAL APPLICATION CIRCUITS
D1
VIN
C3
B0530
JP1
U1
R5
Bias
Bias
100
1
C4
2
3
PWMA
PWMB
EN
R6
4
10k
R7
5
10k
R8
6
MP3308
SW
GND
PGND
ISET
IN
LED
PWMIA
OVP
PWMIB
GND
EN
PWMOA
FSET
PWMOB
14
R1
1
R2
NS
C5
NC
R3
160k
13
LED+
C10
33nF
12
LED-
11
C6
NS
10
R4
10k
9
10k
R9
100k
R10
100k
R11
100k
C7
10nF
7
8
C8
68nF
C9
68nF
VIN Bias Circuit
LED+
R12
900
Bias
D2
Figure 4— Driving 27 WLEDs (9 WLEDs in Series and 3 Strings Paralleled) with 3V-3.3V Input Voltage1
(1) Use additional bias circuit for low input voltage compatibility.
MP3308 Rev. 1.02
7/19/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
12
MP3308 – STEP-UP WHITE LED DRIVER WITH DUAL PWM DIMMING INPUT CONTROL
PACKAGE INFORMATION
QFN14 (3x4mm)
2.90
3.10
1.60
1.80
0.30
0.50
PIN 1 ID
MARKING
PIN 1 ID
SEE DETAIL A
1
14
0.18
0.30
3.20
3.40
3.90
4.10
PIN 1 ID
INDEX AREA
0.50
BSC
8
TOP VIEW
7
BOTTOM VIEW
0.80
1.00
0.20 REF
PIN 1 ID OPTION A
0.30x45º TYP.
PIN 1 ID OPTION B
R0.20 TYP.
0.00
0.05
SIDE VIEW
DETAIL A
2.90
0.70
NOTE:
1.70
1) ALL DIMENSIONS ARE IN MILLIMETERS.
2) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH.
3) LEAD COPLANARITY SHALL BE0.10 MILLIMETER MAX.
4) JEDEC REFERENCE IS MO-229, VARIATION VGED-4.
5) DRAWING IS NOT TO SCALE.
0.25
3.30
0.50
RECOMMENDED LAND PATTERN
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.
MP3308 Rev. 1.02
7/19/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
13
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