MP3397 [MPS]
Step-Up, 4-String Max 350mA/String White LED Driver;
| 型号： | MP3397 |
| 厂家： | 
MONOLITHIC POWER SYSTEMS |
| 描述： | Step-Up, 4-String Max 350mA/String White LED Driver |
| 文件： | 总16页 (文件大小：396K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MP3397
Step-Up, 4-String
Max 350mA/String White LED Driver
The Future of Analog IC Technology
DESCRIPTION
FEATURES
4-String, Max 350mA/String at 10% DPWM
5V to 28V Input Voltage Range
2.5% Current Matching Accuracy Between
Strings
The MP3397 is a step-up controller with 4
current channels designed to drive WLED
arrays for large-size LCD-panel backlighting
applications. The MP3397 is flexible, and can
expand the number of LED channels with two
or more MP3397s in parallel operating from a
single inductive power source.
Programmable Switching Frequency
PWM or DC Input Burst PWM Dimming
Open and Short LED Protection
Programmable Over-Voltage Protection
Cascading Capability with a Single Power
Source
The MP3397 uses current-mode fixed-
frequency architecture. An external resistor sets
the switching frequency. This signal drives an
external MOSFET to boost up the output
voltage from 5V to a 28V input supply. The
MP3397 regulates the current in each LED
string to the programmed value set by an
external current-setting resistor.
Under-Voltage Lockout
Thermal Shutdown
16-pin TSSOP，SOIC Package
APPLICATIONS
Desktop LCD Flat Panel Displays
Flat Panel Video Displays
2D/3D LCD TVs and Monitors
The MP3397 applies 4 internal current sources
for current balance. The current matching can
achieve 2.5% regulation accuracy between
strings. Its low regulation voltage on LED
current sources reduces power loss and
improves efficiency.
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.
An external PWM input signal or DC input
signal controls PWM dimming. The dimming
PWM signal can be generated internally and
the dimming frequency is programmed by an
external setting capacitor.
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
1
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
TYPICAL APPLICATION
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
2
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
ORDERING INFORMATION
Part Number
MP3397EF*
MP3397ES**
Package
TSSOP16
SOIC16
Top Marking
MP3397
MP3397
*For Tape & Reel, add suffix –Z (eg. MP3397EF–Z).
For RoHS compliant packaging, add suffix –LF (eg. MP3397EF–LF–Z)
**For Tape & Reel, add suffix –Z (eg. MP3397ES–Z).
For RoHS compliant packaging, add suffix –LF (eg. MP3397ES–LF–Z)
PACKAGE REFERENCE
TSSOP16
SOIC16
Thermal Resistance (4)
TSSOP16................................45 ...... 10...°C/W
SOIC16 ...................................80 ...... 35...°C/W
θJA
θJC
ABSOLUTE MAXIMUM RATINGS (1)
VIN................................................-0.3V to +30V
V
GATE ............................................-0.5V to +6.8V
VCC .............................................-0.5V to +6.8V
LED1 to VLED4....................................-1V to +55V
Notes:
V
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.
All Other Pins...............................-0.3V to +6.3V
(2)
Continuous Power Dissipation (TA = 25°C)
TSSOP16................................................ 2.78 W
SOIC16................................................... 1.56 W
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.............................5V to 28V
LED Current (Backlight) ...........10mA to 350mA
Operating Junction Temp. (TJ).-40°C to +125°C
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
3
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
ELECTRICAL CHARACTERISTICS
VIN =12V, VEN = 5V, TA = 25°C, unless otherwise noted.
Parameters
Symbol
VIN
Condition
Min
Typ
Max Units
Operating Input Voltage
Supply Current (Quiescent)
5
28
V
VIN=12V, VEN=5V, no load with
switching
IQ
4
mA
Supply Current (Shutdown)
LDO Output Voltage
IST
VEN=0V, VIN=12V
2
μA
VEN=5V,
0<IVCC<10mA
7V<VIN<28V,
VCC
5.5
3.8
6
6.5
4.6
V
Input UVLO Threshold
Input UVLO Hysteresis
EN High Voltage
VIN_UVLO
Rising Edge
4.2
V
mV
V
200
VEN_HIGH
VEN_LOW
VEN Rising
VEN Falling
1.8
EN Low Voltage
0.6
V
STEP-UP CONVERTER
Gate Driver Impedance
(Sourcing)
Gate Driver Impedance
(Sinking)
VCC=6V,VGATE=6V
4
2
Ω
Ω
VCC=6V,IGATE=10mA
R
OSC= 115kΩ
480
145
1.20
540
165
600
185
kHz
kHz
V
Switching Frequency
fSW
ROSC= 374kΩ
OSC Voltage
VOSC
tON_MIN
DMAX
1.23 1.26
100
PWM Mode,
when no pulse skipping happens
Minimum On Time
ns
Maximum Duty Cycle
ISENSE Limit
90
%
mV
μA
μA
Max Duty Cycle
150
200
65
250
COMP Source Current Limit
COMP Sink Current Limit
PWM DIMMING
ICOMP SOLI
ICOMP SILI
15
DBRT Leakage Current
BOSC Frequency
IDBRT_LK
fBOSC
-5
1.0
6
5
2
9
μA
kHz
μA
CBOSC=2.2nF
1.5
7.5
BOSC Output Current
LED CURRENT REGULATION
ISET Voltage
IBOSC
VISET
ILED
1.20
31
1.23 1.25
V
mA
%
LEDX Average Current
Current Matching (5)
RISET=30kꢀ
32
33
ILED=32mA
2.5
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
4
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
ELECTRICAL CHARACTERISTICS (continued)
VIN =12V, VEN = 5V, TA = 25°C, unless otherwise noted.
Parameters
Symbol Condition
VLEDX ILED=180mA
Min
Typ
Max Units
LEDX Regulation Voltage
PROTECTION
390
mV
OVP(Over Voltage Protection)
Threshold
VOVP_OV Rising Edge
1.20
1.23 1.26
V
OVP UVLO threshold
LEDX UVLO Threshold
LEDX Over Voltage Threshold
Thermal Shutdown Threshold
Notes:
VOVP_UV Step-up Converter Fails
50
156
5.8
70
196
6.3
90
236
6.8
mV
mV
V
VLEDX_UV
VLEDX_OV
TST
150
°C
5) Matching is defined as the difference of the maximum to minimum current divided by 2 times average currents.
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
5
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
PIN FUNCTIONS
Pin #
Name
Description
Step-up Converter Compensation Pin. This pin compensates the regulation control loop.
Connect a ceramic capacitor from COMP to GND.
1
COMP
Enable Control Input. Turn-on threshold at 1.8V. Turn-off threshold at 0.6 V. Do not
let this pin float.
2
3
EN
Brightness Control Input. Apply a PWM signal on this pin for for external PWM dimming
mode. Apply a DC voltage range from 0.2V to 1.2V on this pin to linearly set the internal
dimming duty cycle from 0% to 100% for DC-input PWM dimming mode. The MP3397 has
positive dimming polarity on DBRT.
DBRT
4
5
GND
OSC
Ground.
Switching Frequency Set. Connect a resistor between OSC and GND to set the step-up
converter switching frequency. The voltage at this pin is regulated to 1.23V. The clock
frequency is proportional to the current sourced from this pin.
LED Current Set. Tie a current-setting resistor from this pin to ground to program the
current in each LED string. This pin voltage is regulated to 1.23V. The LED current is
proportional to the current through the ISET resistor.
6
7
ISET
Dimming Repetition Set. This is the timing pin for the oscillator to set the dimming
frequency. To use DC input PWM dimming mode, connect a capacitor from this pin to
GND to set the internal dimming frequency. A saw-tooth waveform is generated on this
pin. To use external PWM dimming mode, connect a resistor from this pin to GND, and
apply the PWM signal on DBRT pin.
BOSC
LED String 4 Current Input. This pin is the open-drain output of an internal dimming
control switch. Connect the LED String 4 cathode to this pin.
8
9
LED4
LED3
LED String 3 Current Input. This pin is the open-drain output of an internal dimming
control switch. Connect the LED String 3 cathode to this pin.
LED String 2 Current Input. This pin is the open-drain output of an internal dimming
control switch. Connect the LED String 2 cathode to this pin.
10
11
LED2
LED1
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.
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 MP3397 triggers
Over Voltage Protection mode.
12
13
OVP
Current Sense Input. During normal operation, this pin senses the voltage across the
external-inductor current-sensing resistor (RSENSE) for peak-current–mode control and also
to limit the inductor current during every switching cycle. If this pin is not used for
cascading applications, tie this pin to GND; do not let this pin float.
ISENSE
Step-up Converter Power Switch Gate Output. This pin drives the external power N-MOS
device.
14
15
GATE
VIN
Supply Input. VIN supplies the power to the chip, as well as the step-up converter switch.
Drive VIN with a 5V to 28V power source. Must be locally bypassed.
The Internal 6V Linear Regulator Output. VCC provides power supply for the external
MOSFET switch gate driver and the internal control circuitry. Bypass VCC to GND with a
ceramic capacitor.
16
VCC
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
6
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
TYPICAL PERFORMANCE CHARACTERISTICS
VIN =12V, 10 LEDs in series, 4 strings in parallel, 220mA/string, unless otherwise noted.
Efficiency vs. Vin
Steady State
Vin Startup
100.0%
98.0%
96.0%
94.0%
92.0%
90.0%
88.0%
86.0%
84.0%
82.0%
80.0%
V
V
SW
SW
20V/div.
20V/div.
V
OUT
V
20V/div.
OUT
20V/div.
V
COMP
1V/div.
V
IN
10V/div.
I
I
LED
LED
2A/div.
500mA/div.
10 12 14 16 18 20 22 24 26
INPUT VOLTAGE (V)
Ven Startup
DC Burst Dimming
External PWM Dimming
V
= 0.9V, C
= 2.2nF
f
= 200Hz, D
= 50%
PWM
PWM
BOSC
PWM
V
V
V
SW
SW
SW
20V/div.
20V/div.
20V/div.
V
V
OUT
OUT
V
OUT
20V/div.
20V/div.
20V/div.
V
PWM
V
EN
V
BOSC
5V/div.
5V/div.
1V/div.
I
I
LED
LED
I
LED
500mA/div.
1A/div.
1A/div.
Open LED Protection
Open LED Protection
Short LED Protection
Open all LED strings at working
Open one LED string at working
Short a string at working
V
SW
20V/div.
V
V
SW
SW
20V/div.
20V/div.
V
OUT
20V/div.
V
V
V
LED1
OUT
OUT
20V/div.
20V/div.
20V/div.
I
I
LED
I
LED
LED
1A/div.
1A/div.
1A/div.
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
7
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
FUNCTIONAL BLOCK DIAGRAM
VCC
Regulator
VIN
GND
-
Control
Logic
GATE
+
PWM
Comparator
Current Sense
Amplifier
ISENSE
OVP
+
-
OV
Comparator
+
-
Oscillator
OSC
1.23V
LED OV
Comparator
-
6.3V
Short String
Protection
+
-
Feedback
Control
EA
+
COMP
EN
Ref
Enable
Control
LED1
+
1.23V
-
ISET
Current Control
DPWM
Oscillator
BOSC
DBRT
DPWM
Comparator
LED4
-
+
Figure 1—MP3397 Functional Block Diagram
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
8
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
OPERATION
The MP3397 employs a programmable constant-
frequency, peak-current–mode step-up converter
with 4 channels or regulated current sources to
drive an array of up to 4 strings of white LEDs.
The output voltage of the internal error amplifier
is an amplified signal of the difference between
the reference voltage and the feedback voltage.
The converter automatically chooses the lowest
active LEDX pin voltage to provide a high-
enough bus voltage to power all the LED arrays.
Internal 6V Regulator
The MP3397 includes an internal linear regulator
(VCC). When VIN is greater than 6.5V, this
regulator outputs a 6V power supply to the
external MOSFET switch gate driver and the
internal control circuitry. The VCC voltage drops
to 0V when the chip shuts down. The MP3397
features under-voltage lockout (UVLO). The chip
is disabled until VCC exceeds the UVLO
threshold. The UVLO hysteresis is approximately
200mV.
If the feedback voltage drops below the
reference, the output of the error amplifier
increases. This result in more current flowing
through the MOSFET, thus increasing the power
delivered to the output. This forms a closed loop
that regulates the output voltage.
Under light-load operation—where VOUT ≈ VIN—
the converter runs in pulse-skipping mode where
the MOSFET turns on for a minimum on-time of
approximately 100ns, and then the converter
discharges the power to the output for the
remaining period. The external MOSFET remains
off until the output voltage needs to be boosted
again.
System Startup
When enabled, the MP3397 checks the topology
connection first. The chip monitors the over-
voltage protection (OVP) pin to see if the
Schottky diode is not connected or if the boost
output is shorted to GND. An OVP voltage of less
than 70mV will disable the chip. The MP3397
also checks other safety limits, including UVLO
and over-temperature protection (OTP) after
passing the OVP test. If all the protection tests
pass, the chip then starts boosting the step-up
converter with an internal soft-start.
Dimming Control
The MP3397 provides two PWM dimming
methods: external PWM signal or DC-input PWM
dimming mode (see Figure 2).
DPWM
Comparator
Ex-PWM Input
DPWM Output
+
-
DBRT
The enable signal must occur after the
establishment of the input voltage and PWM
dimming signal during the start-up sequence.
DPWM
Oscillator
Step-Up Converter
The
converter
operating
frequency
is
BOSC
C
BOSC
programmable (from 150kHz to 500kHz) with an
external set resistor on the OSC pin. This
flexibility helps to optimize the size of external
components and improve the efficiency.
Figure 2—PWM Dimming Method
At the beginning of each cycle, the internal clock
turns on the external MOSFET. A stabilizing
ramp added to the output of the current sense
amplifier prevents sub-harmonic oscillations for
duty cycles greater than 50 percent. This result is
fed into the PWM comparator. When this
resulting voltage rises to the level of the error
amplifier output voltage (VCOMP), the external
MOSFET turns off.
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
9
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
For external PWM dimming, ground the BOSC
pin through a resistor, and apply an external
PWM signal to the DBRT pin.
The MP3397 will always attempt to light at least
one string. If all strings are open, the MP3397
shuts down the step-up converter. The strings
will remain in this marked state until the chip
reset.
For DC-input PWM dimming, apply a DC analog
signal to the DBRT pin, and connect a capacitor
from BOSC to ground. The DC signal is then
converted to a DPWM dimming signal with a
proportional oscillation frequency.
Short String Protection
The MP3397 monitors the LEDX pin voltages to
determine if a short string fault has occurred. If
one or more strings are shorted, the
corresponding LEDX pins tolerate this higher
voltage. If an LEDX pin voltage is higher than
6.3V, this condition triggers the detection of a
short string. When a short string fault (LEDX
over-voltage fault) continues for 4096 switching
cycles, the fault string is marked OFF and
disabled. Once a string is marked OFF, it
disconnects from the output voltage loop. The
marked LED strings shut off completely until the
part restarts. If all strings are shorted, the
MP3397 will shut down the step-up converter.
The strings remain marked OFF until the chip
resets.
The brightness of the LED array is proportional to
the duty cycle of the DPWM signal. The DPWM
signal frequency is set by the capacitor from the
BOSC pin to ground.
Open String Protection
Open string protection is achieved through the
OVP pin and the LED (1 to 4) pins. 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 reaches the over-voltage
protection (OVP) threshold. Then the chip marks
which strings have an LEDX pin voltage lower
than 196mV. Once marked, the remaining LED
strings force the output voltage back into tight
regulation. The string with the largest voltage
drop determines the output regulation.
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
10
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
with high efficiency and good EMI performance.
APPLICATION INFORMATION
Calculate the required inductance value using the
equation:
Selecting the Switching Frequency
η VOUT D(1 D)2
L
Set the switching frequency of the step-up
converter from 150kHz to 500kHz for most
applications. An oscillator resistor on OSC pin
sets the internal oscillator frequency for the step-
up converter according to the equation:
2 fSW ILOAD
VIN
D 1
VOUT
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.
62100
f
SW(kHz)
ROSC(k)
The switching current is usually used for the peak
current mode control. In order to avoid hitting the
current limit, the voltage across the sensing
resistor RSENSE must measure less than 80% of
For ROSC=330kꢀ, the switching frequency is set
to 188kHz.
Setting the LED Current
The LED string currents are identical and set
through the current setting resistor on the ISET
pin.
the worst-case current-limit voltage, VSENSE
.
0.8 VSENSE
RSENSE
IL(PEAK)
790 1.23V
ILED (mA)
(RSET +0.4)k
VOUT ILOAD
V (VOUT -V )
2L fSW VOUT
IN
IN
IL(PEAK)
ηV
IN
For RSET=7.68kꢀ, the LED current is set to
120mA. The ISET pin can not be open.
Where IL(PEAK) is the peak value of the inductor
current. VSENSE is shown in Figure 3.
Selecting the Input Capacitor
Vsense vs. Duty Cycle
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
the high-frequency switching current from
passing through to the input. Use ceramic
capacitors with X5R or X7R dielectrics for their
low ESR and small temperature coefficients. For
most applications, use a 4.7μF ceramic capacitor
in parallel with a 220µF electrolytic capacitor.
500
400
300
200
100
0
0 10 20 30 40 50 60 70 80 90100
DUTY CYCLE (%)
Selecting the Inductor and Current Sensing
Resistor
Figure 3—VSENSE vs Duty Cycle
The MP3397 requires an inductor to supply a
higher output voltage while being driven by the
input voltage. A larger value inductor results in
less ripple current, resulting in lower peak
inductor current and reducing stress on the
internal N-channel MOSFET. However, larger-
value inductors have a larger physical size,
higher series resistance, and lower saturation
current.
Selecting the Power MOSFET
The MP3397 is capable of driving a wide variety
of N-channel power MOSFETS. The critical
parameters of selection of a MOSFET are:
1. Maximum drain-to-source voltage, VDS(MAX)
2. Maximum current, ID(MAX)
3. On-resistance, RDS(ON)
4. Gate source charge QGS and gate drain
charge QGD
Choose an inductor that does not saturate under
the worst-case load conditions. Select the
minimum inductor value to ensure that the boost
converter works in continuous conduction mode
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
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11
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
5. Total gate charge, QG
The total gate charge, QG, is used to calculate
the gate drive loss. The expression is
Ideally, the off-state voltage across the MOSFET
is equal to the output voltage. Considering the
voltage spike when it turns off, VDS(MAX) should be
greater than 1.5 times of the output voltage.
PDR QG VDR fSW
Where VDR is the drive voltage.
Selecting the Output Capacitor
The maximum current through the power
MOSFET occurs at the maximum input voltage
and the maximum output power. The maximum
RMS current through the MOSFET is given by
The output capacitor keeps the output voltage
ripple small and ensures feedback loop stability.
The output capacitor impedance must be low at
the switching frequency. Ceramic capacitors with
X7R dielectrics are recommended for their low
ESR characteristics. For most applications, a
4.7μF ceramic capacitor in parallel with a 22μF
electrolytic capacitor will suffice.
, where:
IRMS(MAX) IIN(MAX) DMAX
VOUT V
IN(MIN)
DMAX
VOUT
The current rating of the MOSFET should be
greater than 1.5xIRMS
Setting the Over Voltage Protection
The open string protection is achieved through
the detection of the voltage on the OVP pin. 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, OVP will trigger.
The ON resistance of the MOSFET determines
the conduction loss, which is given by:
2
Pcond IRMS RDS (on) k
Where k is the temperature coefficient of the
MOSFET.
To ensure the chip functions properly, select the
resistor values for the OVP resistor divider to
provide an appropriate set voltage. The
recommended OVP point is about 1.1 to 1.2
times higher than the output voltage for normal
operation.
The switching loss is related to QGD and QGS1
which determine the commutation time. QGS1 is
the charge between the threshold voltage and
the plateau voltage when a driver charges the
gate, which can be read in the chart of VGS vs. QG
of the MOSFET datasheet. QGD is the charge
during the plateau voltage. These two
parameters are needed to estimate the turn-on
and turn-off losses.
RHIGH
VOVP 1.23(1
)
RLOW
Selecting Dimming Control Mode
The MP3397 provides two different dimming
methods
QGS1 RG
PSW
VDS IIN fSW
VDS IIN fSW
VDR VTH
QGD RG
VDR VPLT
1. Direct PWM Dimming
An external PWM dimming signal is employed to
achieve PWM dimming control. Connect a 100kꢀ
resistor from BOSC pin to GND and apply a
PWM dimming signal—in the range of 100Hz to
20kHz—to the DBRT pin. The minimum
recommended amplitude of the PWM signal is
1.2V. The low level should be less than 0.4V
(See Figure 4).
Where VTH is the threshold voltage, VPLT is the
plateau voltage, RG is the gate resistance, and
VDS is the drain-source voltage. Please note that
calculating the switching loss is the most difficult
part in the loss estimation. The formula above
provides a simplified equation. For more accurate
estimates, the equation becomes much more
complex.
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
12
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
Expanding LED Channels
The MP3397 can expand the number of LED
channels by using two or three MP3397s in
parallel. To connect two MP3397s for a total of 8
LED strings, tie the VCC pins of the master IC
and the slave IC together to power the slave IC
internal logic circuitry. Tie the COMP pins of the
slave IC and the master IC together to regulate
the voltage of all 8 strings LEDs. The slave IC
MOSFET driving signals are not used; the boost
converter can be only driven by the master IC.
Do not leave the ISENSE pin of the slave IC
floating; tie it to ground. Apply the EN and DIM
signals to both ICs. For best results, use external
PWM dimming mode for synchronized and
accurate dimming.
Figure 4—Direct PWM Dimming
Table 1 shows the PWM dimming duty Range
with different PWM dimming frequency.
Tab 1 The Range of PWM Dimming Duty
fPWM(Hz)
100<f200
200<f500
500<f1k
1k<f2k
2k<f5k
5k<f10k
10k<f20k
Dmin
Dmax
0.30%
0.75%
1.50%
3.00%
7.50%
15.00%
30.00%
100%
100%
100%
100%
100%
100%
100%
Layout Considerations
The circuit layout for the MP3397 requires
special attention to reduce EMI noise.
The loop from the external MOSFET (M1),
through the output diode (D1) and the output
capacitor (C2, C3) carry a high-frequency pulse
current and must be as small and short as
possible (See Figure 6).
2. DC Input PWM Dimming
For DC input PWM dimming, apply an analog
signal (ranging from 0.2 V to 1.2V) to the DBRT
pin to modulate the LED current directly. If the
DBRT voltage falls below 0.2V, the PWM duty
cycle will be 0%. If the DBRT voltage goes above
1.2V, the output will be 100% (See Figure 5). The
capacitor on BOSC pin sets the frequency of the
internal triangle waveform according to the
equation.
f
BOSC (kHz)= 3.5 / CBOSC(nF)
Chose a dimming frequency in the range of
100Hz to 20kHz.
Figure 6—Layout Consideration
All logic signals return to the signal ground. In
order to reduce the effects of noise, separate
power ground (PGND) and signal ground (GND),
and connect PGND and GND together through
single point.
Figure 5—DC input PWM Dimming
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
13
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
TYPICAL APPLICATION CIRCUIT
C2
C3
C4 C5
C1
D1
L1
F1
VIN
NC
LED
B390
R2
464k
R3
100V/4A
M1
C6
C8
10
LED1
GND
LED2
LED3
LED4
R4
10k
R5
0
NC
15
16
1
14
13
4
VIN
GATE
ISENSE
GND
C9
C10
R6
VCC
COMP
EN
0.05
R7
EN
200
470nF
R8
2k
2
12
11
10
9
OVP
U1
0
0
0
R9
R12
R13
R15
R10
220k
5
OSC
BOSC
DBRT
ISET
LED1
LED2
LED3
LED4
R11
20k
C11
NC
MP3397
7
C12
NC
R14
100k
3
0
6
8
DIM
R16
2k
R17
C13
NC
R18
20k
2.55k
Figure 7—Drive 14 LEDs in Series, 4 Strings 330mA/string,10% DPWM
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
14
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
PACKAGE INFORMATION
TSSOP16（with external thermal pad）
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
15
MP3397—4-STRING, MAX 350mA/STRING WHITE LED DRIVER
PACKAGE INFORMATION
SOIC16
0.386( 9.80)
0.394(10.00)
0.024(0.61)
0.050(1.27)
9
16
0.063
(1.60)
0.150
(3.80)
0.157
(4.00)
0.228
(5.80)
0.244
(6.20)
0.213
(5.40)
PIN 1 ID
8
1
TOP VIEW
RECOMMENDED LAND PATTERN
0.053(1.35)
0.069(1.75)
SEATING PLANE
0.0075(0.19)
0.0098(0.25)
0.050(1.27)
BSC
0.013(0.33)
0.020(0.51)
0.004(0.10)
0.010(0.25)
SEE DETAIL "A"
SIDE VIEW
FRONT VIEW
NOTE:
0.010(0.25)
0.020(0.50)
x 45o
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 0.004" INCHES MAX.
5) DRAWING CONFORMS TO JEDEC MS-012, VARIATION AC.
6) DRAWING IS NOT TO SCALE.
0.016(0.41)
0.050(1.27)
0o-8o
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.
MP3397 Rev. 1.01
9/4/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
16
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