MP3388DR-LF-Z [MPS]
LED Driver, 8-Segment, 4 X 4 MM, HALOGEN FREE AND ROHS COMPLIANT, MO-220VGGD, QFN-24;
| 型号： | MP3388DR-LF-Z |
| 厂家： | 
MONOLITHIC POWER SYSTEMS |
| 描述： | LED Driver, 8-Segment, 4 X 4 MM, HALOGEN FREE AND ROHS COMPLIANT, MO-220VGGD, QFN-24 驱动 接口集成电路 |
| 文件： | 总14页 (文件大小：371K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MP3388
50V, 8-String White LED Driver
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP3388 is a step-up converter with
8-channel current sources designed for driving
the white LED arrays for large size LCD panel
backlighting applications.
•
•
•
•
•
High Efficiency and Small Size
4.5V to 25V Input Voltage Range
50V Maximum Step-up Voltage
Balanced Driver for 8 Strings of WLED
3% Current Matching Accuracy Between
Strings
Selectable Switching Frequency: 1.25MHz or
625kHz
PWM or DC Input Burst PWM Dimming
Programmable Over-voltage Protection
Under Voltage Lockout
The MP3388 uses current mode, fixed frequency
architecture. The switching frequency can be
selected at 1.25MHz or 625kHz. It generates an
output voltage up to 50V from a 4.5V to 25V input
supply. The MP3388 independently regulates the
current in each LED string to the user programmed
value set by an external current setting resistor.
•
•
•
•
•
•
•
Open and Short LED protection
Thermal Shutdown
Small QFN24 (4x4mm) and 28 pin SOIC
packages
The MP3388 applies 8 internal current sources in
each LED string terminal to achieve a current
balance of 3% regulation accuracy between
strings. Its low 600mV regulation voltage on LED
current sources reduces power loss and improves
efficiency.
•
Halogens Free
APPLICATIONS
The MP3388 features external PWM dimming or
DC input PWM dimming, which allows the flexible
control of the backlighting luminance. The dimming
PWM signal can be generated internally, and the
dimming frequency is programmed by an external
setting capacitor.
•
•
•
•
Notebook PC
Small LCD TV
Handy Terminals Display
Automotive System and Tablet Computer
All MPS parts are lead-free and adhere to the RoHS directive. For MPS green
status, please visit MPS website under Quality Assurance.
“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of
Monolithic Power Systems, Inc.
TYPICAL APPLICATION
M1
L1
D1
VIN
C1
C2
R1
R2
4.5V~25V
C4
C3
24
VCC
23
VIN
22
21
20
19
SW2
PGND1
COMP VFAULT SW1
1
2
3
4
18
EN
Enable
17
16
15
14
13
OSC
PGND2
OVP
NC
FSET
MP3388
PWMO
GND
LED1
LED2
LED3
C5
C6
5
6
PWM
PWMI
DIMMING
LED8
LED7
8
LED6
9
LED5
10
ISET
11
LED4
12
7
R
SET
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
1
MP3388- 50V, 8-STRING WHITE LED DRIVERS
ORDERING INFORMATION
Part Number
MP3388DR*
MP3388EY
Package
Top Marking
3388DR
Free Air Temperature (TA)
-40°C TO +85°C
QFN24 (4x4mm)
SOIC28
MP3388EY
-20°C TO +85°C
* For Tape & Reel, add suffix –Z (e.g. MP3388DR–Z).
For RoHS Compliant Packaging, add suffix –LF (e.g. MP3388DR–LF–Z)
PACKAGE REFERENCE
TOP VIEW
TOP VIEW
VFAULT
COMP
VIN
SW1
NC
1
2
28
27
26
25
24
23
22
21
20
19
18
17
16
15
24
23 22
21
20 19
SW2
NC
3
VCC
4
1
2
3
4
5
6
18
17
16
15
14
13
EN
OSC
PGND1
PGND2
OVP
EN
PGND1
PGND2
OVP
LED1
LED2
LED3
LED4
NC
5
OSC
6
FSET
PWMO
GND
Exposed Pad
Connect to GND
7
FSET
PWMO
GND
8
LED1
LED2
LED3
9
PWMI
LED8
LED7
LED6
LED5
10
11
12
13
14
PWMI
7
8
9
10 11
12
ISET
NC
QFN24 (4X4mm)
SOIC28
ABSOLUTE MAXIMUM RATINGS (1)
Thermal Resistance (4)
θJA
θJC
VIN .................................................-0.3V to +30V
QFN24 (4x4mm) ...................42 ....... 9....°C/W
SOIC28 .................................60 ...... 30...°C/W
VVFAULT...........................................VIN - 6V to VIN
VSW................................................-0.3V to +50V
VLED1 to VLED8.................................-0.3V to +50V
All Other Pins..................................-0.3V to +6V
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 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.
Continuous Power Dissipation
(TA = +25°C) (2)
QFN24 (4x4mm)………………………….....2.9W
SOIC28…………………………… ……....2.1W
Junction Temperature...............................150°C
Lead Temperature ....................................260°C
Storage Temperature............... -65°C to +150°C
3) The device is not guaranteed to function outside of its
operation conditions.
4) Measured on JESD51-7, 4-layer PCB.
Recommended Operating Conditions (3)
Supply Voltage VIN ...........................4.5V to 25V
Maximum Junction Temp. (TJ)..................125°C
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
2
MP3388- 50V, 8-STRING WHITE LED DRIVERS
ELECTRICAL CHARACTERISTICS
VIN =12V, VEN = 5V, TA = +25°C, unless otherwise noted.
Parameters
Symbol Condition
Min
Typ
Max Units
Operating Input Voltage
VIN
4.5
25
V
Supply Current (Quiescent)
IQ
IST
VIN=12V, VEN=5V, no load.
1.8
mA
Supply Current (Shutdown)
LDO Output Voltage
VEN=0V, VIN=12V
2
μA
VEN=5V, 6V<VIN<25V,
0<IVCC<10mA
VCC
4.5
3.4
5
5.5
4.3
V
Input UVLO Threshold
Input UVLO Hysteresis
EN ON Threshold
VIN_UVLO Rising Edge
3.9
V
mV
V
200
VEN_ON
VEN Rising
1.8
EN OFF Threshold
VEN_OFF VEN Falling
0.6
V
STEP-UP CONVERTER
SW On-Resistance
SW Leakage Current
RDS_ON
ISW_LK
IDS=20mA
0.18
0.3
1
Ω
μA
MHz
kHz
V
VSW=45V
VOSC=VCC or Floating
1.0
500
2.1
1.25
625
1.5
750
Switching Frequency
fSW
VOSC=0V
OSC High-Level Threshold
OSC Low-Level Threshold
VOSC_H
VOSC_L
TON_MIN
DMAX
ISW_LIMIT Duty=90%
GCOMP ΔICOMP=±10uA
ICOMP
0.8
96
V
PWM Mode,
when no pulse skipping happens
Minimum On Time
100
93
ns
Maximum Duty Cycle
SW Current Limit
90
%
A
2.0
COMP Transconductance
COMP Output Current
100
60
μA/V
uA
PWM DIMMING
PWMI High-Level Threshold
PWMI Low-Level Threshold
PWMO Output Impedance
PWMI Leakage Current
DPWM Frequency
VPWMI_H
VPWMI_L
RPWMO
IPWMI_LK
fDPWM
1.5
V
V
0.8
500
+1
2
300
-1
400
1.6
kΩ
μA
kHz
CFSET=2.2nF
1.2
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
3
MP3388- 50V, 8-STRING WHITE LED DRIVERS
ELECTRICAL CHARACTERISTICS (continued)
VIN =12V, VEN = 5V, TA = +25°C, unless otherwise noted.
Parameters
Symbol Condition
Min
Typ
Max Units
LED CURRENT REGULATION
LEDX Average Current
Current Matching (5)
ILED
RISET=60.4kꢀ
ILED=20mA
19.2
19.9 20.6
mA
%
3
Maximum LED Current per String
LEDX Regulation Voltage
ILEDmax
VLEDX
RISET=40.2 kꢀ
ILED=20mA
30
mA
mV
600
PROTECTION
OVP Over Voltage Threshold
OVP UVLO threshold
VOVP_OV Rising Edge
VOVP_UV Step-up Converter Fails
VLEDX_OV VIN>5.5V
VLEDX_UV
1.17
48
1.23
70
1.3
102
5.9
V
mV
V
LEDX Over Voltage Threshold
LEDX UVLO Threshold
5.1
5.5
175
150
1.6
55
130
230
mV
℃
Thermal Shutdown Threshold
LEDX Over Voltage Fault Timer
VFAULT Pull Down Current
TST
1.3
40
1.9
70
ms
μA
IFAULT
VFAULT Blocking-Off Voltage
(with Respect to VIN)
VFAULT
VIN =12V, VIN-VFAULT
6
V
Notes:
5) Matching is defined as the difference of the maximum to minimum current divided by 2 times average currents.
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
4
MP3388- 50V, 8-STRING WHITE LED DRIVERS
PIN FUNCTIONS
QFN24 SOIC28 Name Description
1
2
5
6
EN
Enable Control Input. Do not let this pin floating.
Switching Frequency Selection Input. When float this pin or connect this pin to
OSC VCC, the step-up converter switching frequency is 1.25MHz. When connect this
pin to GND, the step-up converter switching frequency is 625kHz.
Dimming PWM Frequency Setting. Connect a capacitor between FSET and GND
FSET
3
7
to set the DPWM frequency by the equation: fDPWM=3.5uF/CFSET
.
PWM Filter Output. To use external PWM dimming mode, connect a capacitor
between PWMO and GND to form a low-pass filter with an internal 400kꢀ resistor.
It filters the external PWM logic signal on PWMI pin into a DC signal whose level is
inversely proportional to the duty-cycle of the input PWM signal. Then the DC
signal is converted to a DPWM dimming signal with the same duty-cycle as the
external PWM signal. To use DC input PWM dimming mode, directly apply a DC
voltage from 0.2V to 1.2V on PWMO pin for dimming PWM duty cycle control. The
DC input PWM dimming polarity is negative.
4
8
PWMO
5
6
9
GND Analog Ground.
PWM Signal Input. To use the external PWM dimming mode, apply a PWM signal
on this pin for brightness control. This signal is filtered and its duty cycle is
PWMI converted into a DC signal to calculate the DPWM duty cycle. And the DPWM duty
cycle equals to the input PWM duty cycle. To use DC input PWM dimming mode,
float this pin.
10
LED String 8 Current Input. This pin is the open-drain output of an internal
LED8 dimming control switch. Connect the LED String 8 cathode to this pin. If this string
is not used, connect Vout to this pin.
7
8
9
11
12
13
LED String 7 Current Input. This pin is the open-drain output of an internal
LED7 dimming control switch. Connect the LED String 7 cathode to this pin. If this string
is not used, connect Vout to this pin.
LED String 6 Current Input. This pin is the open-drain output of an internal
LED6 dimming control switch. Connect the LED String 6 cathode to this pin. If this string
is not used, connect Vout to this pin.
LED String 5 Current Input. This pin is the open-drain output of an internal
LED5 dimming control switch. Connect the LED String 8 cathode to this pin. If this string
is not used, connect Vout to this pin.
10
11
12
14
16
18
LED Current Setting. Tie a current setting resistor from this pin to ground to
program the current in each LED string. ILED = 1000 x 1.22V /( RSET+1kꢀ)
ISET
LED String 4 Current Input. This pin is the open-drain output of an internal
LED4 dimming control switch. Connect the LED String 4 cathode to this pin. If this string
is not used, connect Vout to this pin.
LED String 3 Current Input. This pin is the open-drain output of an internal
LED3 dimming control switch. Connect the LED String 3 cathode to this pin. If this string
is not used, connect Vout to this pin.
13
14
19
20
LED String 2 Current Input. This pin is the open-drain output of an internal
LED2 dimming control switch. Connect the LED String 2 cathode to this pin. If this string
is not used, connect Vout to this pin.
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
5
MP3388- 50V, 8-STRING WHITE LED DRIVERS
PIN FUNCTIONS (continued)
QFN24
SOIC28
Name
Description
LED String 1 Current Input. This pin is the open-drain output of an internal
dimming control switch. Connect the LED String 1 cathode to this pin. If this
string is not used, connect Vout to this pin.
15
21
LED1
Over-voltage Protection Input. Connect a resistor divider from output to this
pin to program the OVP threshold. When this pin voltage reaches 1.23V, the
MP3388 triggers OV Protection mode.
16
17
18
22
23
24
OVP
PGND2
PGND1
Step-up Converter Power Ground.
Step-up Converter Power Ground. PGND1 and PGND2 should be shorted
externally.
Step-up Converter Power Switch Output. SW2 is the drain of the internal
MOSFET switch. Connect the power inductor and output rectifier to SW2.
SW2 can swing between GND and 50V. SW1 and SW2 should be shorted
externally.
Step-up Converter Power Switch Output. SW1 is the drain of the internal
MOSFET switch. Connect the power inductor and output rectifier to SW1.
SW1 can swing between GND and 50V. SW1 and SW2 should be shorted
externally.
19
20
21
28
26
1
SW2
SW1
Fault Disconnection Switch Driver Output. When the system starts up
VFAULT normally, this pin turns on the external PMOS. When the MP3388 is disabled,
the external PMOS is turned off to disconnect the input and output.
Step-up Converter Compensation Pin. This pin is used to compensate the
22
23
2
3
COMP
VIN
regulation control loop. Connect a capacitor or a series RC network from
COMP to GND.
Supply Input. VIN supplies the power to the MP3388 chip. Drive VIN with a
4.5V to 25V power source. Must be locally bypassed.
The Internal 5V Linear Regulator Output. VCC provides power supply for the
internal MOSFET switch gate driver and the internal control circuitry. Bypass
VCC to GND with a ceramic capacitor. If VIN is less than 5.5V, apply an
external 5V supply directly on VCC.
24
4
VCC
NC
15, 17,
25, 27
No connect
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
6
MP3388- 50V, 8-STRING WHITE LED DRIVERS
TYPICAL PERFORMANCE CHARACTERISTICS
VIN =15V, 10 LEDs in series, 8 strings parallel, 20mA/string, unless otherwise noted.
Steady State
Efficiency vs. Input Voltage
Vin Startup
100
95
V
V
sw
20V/div
sw
20V/div
90
V
OUT
20V/div
V
85
LED8
500mV/div
V
IN
80
10V/div
V
OUT/AC
500mV/div
LED
100mA/div
75
70
I
I
LED
100mA/div
4
9
14
19
24
29
2ms/div
400ns/div
INPUT VOLTAGE (V)
Ven Startup
Open LED Protection
open all LED strings at working
PWM Dimming
fPWM=2kHz, DPWM=50%
V
V
sw
sw
V
sw
20V/div
20V/div
20V/div
V
OUT
20V/div
V
OUT
20V/div
V
V
PWMI
OUT
20V/div
V
5V/div
EN
5V/div
V
FAULT
5V/div
I
I
LED
LED
I
LED
100mA/div
100mA/div
100mA/div
400ms/div
2ms/div
200us/div
Short LED Protection
Short LED Protecton
short Vout to GND at working
short Vout to LEDx at working
V
V
sw
sw
20V/div
20V/div
V
OUT
20V/div
V
OUT
20V/div
V
LED8
20V/div
V
FAULT
10V/div
I
I
LED
LED
100mA/div
100mA/div
1ms/div
200us/div
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
7
MP3388- 50V, 8-STRING WHITE LED DRIVERS
FUNCTION DIAGRAM
VCC
SW
VFAULT
Regulator
VIN
GND
-
Control
Logic
+
PWM
Comparator
Current Sense
Amplifier
+
-
PGND
OVP
OV
Comparator
+
-
Oscillator
OSC
1.23V
LED OV
Comparator
-
5.5V
Short String
Protection
+
-
Max
Feedback
Control
Min
EA
+
COMP
EN
600mV
Enable
Control
LED1
+
1.22V
-
ISET
Current Control
DPWM
Oscillator
LED8
FSET
PWMI
+
-
1.2V
0.2V
DPWM
Comparator
400k?
PWMO
Figure 1—MP3388 Function Diagram
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
8
MP3388- 50V, 8-STRING WHITE LED DRIVERS
OPERATION
output of the current sense amplifier and the
result is fed into the PWM comparator. When this
result voltage reaches the output voltage of the
error amplifier (VCOMP) the power FET is turned
off.
The MP3388 employs a constant frequency, peak
current mode step-up converter and 8-channels
regulated current sources to regulate the array of
8 strings white LEDs. The operation of the
MP3388 can be understood by referring to the
block diagram of Figure 1.
The voltage at the output of the internal error
amplifier is an amplified signal of the difference
between the 600mV reference voltage and the
feedback voltage. The converter automatically
chooses the lowest active LEDX pin voltage for
providing enough bus voltage to power all the
LED arrays.
Internal 5V Regulator
The MP3388 includes an internal linear regulator
(VCC). When VIN is greater than 5.5V, this
regulator offers a 5V power supply for the internal
MOSFET switch gate driver and the internal
control circuitry. The VCC voltage drops to 0V
when the chip shuts down. In the application of
VIN smaller than 5.5V, tie VCC and VIN together.
The MP3388 features Under Voltage Lockout.
The chip is disabled until VCC exceeds the UVLO
threshold. And the hysteresis of UVLO is
approximately 200mV.
If the feedback voltage drops below the 600mV
reference, the output of the error amplifier
increases. It results in more current flowing
through the power FET, thus increasing the
power delivered to the output. In this way it forms
a close loop to make the output voltage in
regulation.
System Startup
At light-load or Vout near to Vin operation, the
converter runs into the pulse-skipping mode, the
FET is turned on for a minimum on-time of
approximately 100ns, and then the converter
discharges the power to the output in the remnant
period. The FET will keep off until the output
voltage needs to be boosted again.
When the MP3388 is enabled, the chip checks
the topology connection first. The VFAULT pin
drives the external Fault Disconnection PMOS to
turn on slowly. And after 400us delay, the chip
monitors the OVP pin to see if the Schottky diode
is not connected or the boost output is short to
GND. If the OVP voltage is lower than 70mV, the
chip will be disabled and the external PMOS is
turned off together. The MP3388 will also check
other safety limits, including UVLO,and OTP after
the OVP test is passed. If they are all in function,
it then starts boosting the step-up converter with
an internal soft-start.
Dimming Control
The MP3388 provides several PWM dimming
methods: external PWM signal from PWMI pin or
DC input PWM Dimming mode (see Figure 2).
These methods results in PWM chopping of the
current in the LEDs for all 8 channels to provide
LED control.
It is recommended on the start up sequence that
the enable signal comes after input voltage and
PWM dimming signal established.
DC Input
DPWM
Comparator
1.2V
Ex-PWM Input
DPWM Output
400k?
-
PWMI
PWMO
Step-up Converter
CPWMO
+
0.2V
The converter operation frequency is selectable
(1.25MHz or 625kHz), which is helpful for
optimizing the external components sizes and
improving the efficiency.
1.2V
0.2V
DPWM
Oscillator
FSET
CFSET
At the beginning of each cycle, the power FET is
turned with the internal clock. To prevent
sub-harmonic oscillations at duty cycles greater
than 50 percent, a stabilizing ramp is added to the
Figure 2—PWM Dimming Method
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
9
MP3388- 50V, 8-STRING WHITE LED DRIVERS
When applying a PWM signal to the PWMI pin,
the MP3388 generates a DC voltage on PWMO
pin which is reversely proportional to the duty
cycle of the PWMI pin signal. By comparing the
PWMO pin signal with the FSET pin triangle
waveform, the converter gets a low frequency
chopping signal that the duty cycle is same as the
input signal. This low frequency chopping signal
will modulate the LED current.
will force the output voltage back into tight
regulation. The string with the highest voltage
drop is the ruling string during output regulation.
The MP3388 always tries to light at least one
string and if all strings in use are open, the
MP3388 shuts down the step-up converter. The
part will maintain mark-off information until the
part shuts down.
Short String Protection
A DC analog signal can be directly applied to the
PWMO pin to modulate the LED current. And the
DC signal is then converted to a DPWM dimming
signal at the setting oscillation frequency. The
polarity is negative.
The MP3388 monitors the LEDX pin voltage to
judge if the short string occurs. If one or more
strings are short, the respective LEDX pins will be
pulled up to the boost output and tolerate high
voltage stress. If the LEDX pin voltage is higher
than 5.5V, the short string condition is detected
on the respective string. When the short string
fault (LEDX over-voltage fault) continues for
greater than 1.6ms, the string is marked off and
disabled. Once a string is marked off, its current
regulation is forced to disconnect from the output
voltage loop regulation. The marked-off LED
strings will be shut off totally until the part restarts.
If all strings in use are short, the MP3388 will shut
down the step-up converter.
The brightness of the LED array is proportional to
the duty cycle of the DPWM signal. The DPWM
signal frequency is set by the cap at the FSET
pin.
Open String Protection
The open string protection is achieved through
the over voltage protection. If one or more strings
are open, the respective LEDX pins are pulled to
ground and the IC keeps charging the output
voltage until it reach OVP threshold. Then the
part will mark off the open strings whose LEDX
pin voltage is less than 175mV. Once the mark-off
operation completes, the remaining LED strings
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
10
MP3388- 50V, 8-STRING WHITE LED DRIVERS
The minimum recommended amplitude of the
PWM signal is 2.1V (See Figure 3)
APPLICATION INFORMATION
Selecting the Switching Frequency
FSET
The switching frequency of the step-up converter
is alternative for 1.25MHz or 625kHz. A bi-level
Switching Frequency Selection (OSC) input sets
the internal oscillator frequency for the step-up
converter. Tie OSC pin to GND corresponds to
the frequency 625kHz and tie OSC pin to VCC or
floating corresponds to 1.25MHz.
C1
MP3388
PWM Dimming
100Hz~50kHz
PWMI
PWMO
C2
Figure 3—PWM Dimming
with Internal Triangle Waveform Generator
Setting the LED Current
The LED string currents are identical and set
through the current setting resistor on the ISET
pin.
2. Direct PWM dimming with positive logic
An external PWM dimming signal is directly
employed to achieve PWM dimming control.
Connect a 100kꢀ resistor from FSET pin to GND
and apply the 100Hz to 2kHz PWM dimming
signal to PWMI pin. The minimum recommended
amplitude of the PWM signal is 1.5V (See Figure
4).
ILED = 1000 x 1.22V / (RSET+1kꢀ)
For RSET=60.4kꢀ, the LED current is set to
19.9mA. The ISET pin can not be open.
Setting the Over Voltage Protection
The open string protection is achieved through
the over voltage protection (OVP). In some cases,
an LED string failure results in the feedback
voltage always zero. The part then keeps
boosting the output voltage higher and higher. If
the output voltage reaches the programmed OVP
threshold, the protection will be triggered.
C1
VCC
FSET
R1
100kO
MP3388
PWM Dimming
100Hz~2kHz
PWMI
PWMO
To make sure the chip functions properly, the
OVP setting resistor divider must be set with a
proper value. The recommended OVP point is
about 1.3 times higher than the output voltage for
normal operation.
Figure 4—Direct PWM Dimming
with Positive Logic
3. Direct PWM dimming with negative logic
VOVP=1.23V x (R1+R2)/R2
It is similar to method 2. Apply a 100Hz to 2 kHz
external square waveform to the PWMO pin for
negative logic PWM dimming. The minimum
recommended amplitude of the PWM signal is
1.5V (See Figure 5),
Selecting Dimming Control Mode
The MP3388 provides 4 different dimming
methods
1. PWM dimming mode with internal triangle
waveform generator
C1
Apply a 100Hz to 50kHz square waveform to the
PWMI pin. The internal 400kꢀ and external
capacitor on PWMO pin filters the dimming signal
to a DC voltage(0.2V~1.2V).Then the DC voltage
is modulated to an internal PWM dimming signal
whose frequency is set via the capacitor on FSET
pin according to the equation:
VCC
FSET
R1
100kO
MP3388
PWMI
PWMO
PWM Dimming
100Hz~2kHz
Figure 5— Direct PWM Dimming
with Negative Logic
fDPWM = 3.5uF / CFSET
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
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© 2011 MPS. All Rights Reserved.
11
MP3388- 50V, 8-STRING WHITE LED DRIVERS
Layout Considerations
4. DC input PWM dimming
To apply DC input PWM dimming, apply an
analog signal (range from 0.2V to 1.2V) to the
PWMO pin to modulate the LED current directly.
If the PWMO is applied with a DC voltage<0.2V,
the PWM duty cycle will be 100%. If the PWMO
pin is applied with a DC voltage>1.2V, the output
will be 0% (See Figure 6). The capacitor on FSET
pin set the frequency of internal triangle
waveform.
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 MP3388 SW to PGND pin
(U1), output diode (D1), and output capacitor (C3)
is flowing with high frequency pulse current. it
must be as short as possible (See Figure 7).
U1
SW
D1
C2
FSET
PGND
C1
MP3388
PWMI
PWMO
Analog Dimming
0.2V~1.2V
GND
Figure 6—DC input PWM dimming
Selecting the Inductor
Iset
Rset
R1
R2
A 10μH (for 1.25MHz switching frequency) /22uH
(for 625kHz switching frequency) inductor with a
DC current rating of at least 40% higher than the
maximum input current is recommended for most
applications. For highest efficiency, the inductor’s
DC resistance should be as small as possible.
Figure 7—Layout Consideration
The IC exposed pad is internally connected to
GND pin, and all logic signals are refer to the
GND. The PGND should be externally connected
to GND and is recommended to keep away from
the logic signals.
Selecting the Input Capacitor
The input capacitor reduces the surge current
drawn from the input supply and the switching
noise from the device. The input capacitor
impedance at the switching frequency should be
less than the input source impedance to prevent
high frequency switching current from passing
through the input. Ceramic capacitors with X5R or
X7R dielectrics are highly recommended because
of their low ESR and small temperature
coefficients. For most applications, a 4.7μF
capacitor is sufficient.
Selecting the Output Capacitor
The output capacitor keeps the output voltage
ripple small and ensures feedback loop stability.
The output capacitor impedance should be low at
the switching frequency. Ceramic capacitors with
X7R dielectrics are recommended for their low
ESR characteristics. For most applications, a
2.2μF ceramic capacitor will be sufficient.
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
12
MP3388- 50V, 8-STRING WHITE LED DRIVERS
PACKAGE INFORMATION
QFN24 (4mm x 4mm)
3.90
4.10
2.50
2.80
PIN 1 ID
SEE DETAIL A
19
24
PIN 1 ID
MARKING
18
13
1
6
0.50
BSC
2.50
2.80
3.90
4.10
PIN 1 ID
INDEX AREA
0.18
0.30
12
7
0.35
0.45
TOP VIEW
BOTTOM VIEW
PIN 1 ID OPTION A
0.30x45º TYP.
PIN 1 ID OPTION B
R0.25 TYP.
0.80
1.00
0.20 REF
0.00
0.05
DETAIL A
SIDE VIEW
3.90
2.70
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 CONFIRMS TO JEDEC MO-220, VARIATION VGGD.
5) DRAWING IS NOT TO SCALE.
0.70
0.25
0.50
RECOMMENDED LAND PATTERN
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
13
MP3388- 50V, 8-STRING WHITE LED DRIVERS
PACKAGE INFORMATION (continued)
SOIC28
0.024
(0.61)
0.050
(1.27)
0.697(17.70)
0.713(18.10)
28
15
0.079
(2.00)
0.291
(7.40)
0.299
(7.60)
0.394
(10.00)
0.418
0.370
(9.40)
(10.60)
PIN 1 ID
14
1
TOP VIEW
RECOMMENDED LAND PATTERN
0.093(2.35)
0.104(2.65)
SEATING PLANE
0.009(0.23)
0.013(0.33)
0.013(0.33)
0.020(0.51)
0.050(1.27)
BSC
0.004(0.10)
0.012(0.30)
SEE DETAIL "A"
FRONT VIEW
SIDE VIEW
0.010(0.25)
0.030(0.75)
x 45o
NOTE:
1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN
BRACKET IS IN MILLIMETERS.
GAUGE PLANE
0.010(0.25) BSC
2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH,
PROTRUSIONS OR GATE BURRS.
3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH
OR PROTRUSIONS.
4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING)
SHALL BE 0.10 MILLIMETERS MAX.
0.016(0.41)
0.050(1.27)
0o-8o
5) DRAWING CONFORMS TO JEDEC MS-013, VARIATION AE.
6) DRAWING IS NOT TO SCALE.
DETAIL "A"
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.
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
14
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