MP3398A
Step up, 4 strings, Max. 350mA/string
An alog and PWM dimming, White LED Controller
MP3398A Rev. 1.03 www.MonolithicPower.com 1
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© 2015 MPS. All Rights Reserved.
The Future of Analog IC Technology
DESCRIPTION
The MP3398A is a step-up controller with 4
current channels, which is designed to drive
WLED arrays for large-size LCD-panel
backlighting applications. It is flexible to expand
the number of LED channels by two or more
ICs in parallel sharing a single inductive power
source.
The MP3398A uses peak-current mode with
fixed switching frequency. The frequency is
programmable by an external setting resistor.
The MP3398A drives an external MOSFET to
boost up the output voltage from a 5V to 28V
input supply. It regulates the current in each
LED string to the value set by an external
current-setting resistor.
The MP3398A 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.
The MP3398A can support both analog and
PWM dimming independently to meet the
different dimming-mode request. In addition,
rich protection modes are also integrated
including OCP, OTP, UVP, OVP, LED
short/open protection, inductor/diode short
protection.
The MP3398A is available in SOIC16,
TSSOP16-EP and SOIC20 packages.
FEATURES
• 4-String, Max 350mA/String WLED Driver
• 5V to 28V Input Voltage Range
• 2.5% Current Matching Accuracy Between
Strings
• Programmable Switching Frequency
• PWM and Analog Dimming Mode
• Cascading Capability with a Single Power
Source
• LED Open and Short LED Protection
• Programmable Over-Voltage Protection
• Recoverable Thermal Shutdown Protection
• Over Current Protection
• Inductor/Diode short Protection
• Under-Voltage Lockout
• SOIC16, TSSOP16-EP and SOIC20
Packages
APPLICATIONS
• Desktop LCD Flat Panel Displays
• Flat Panel Video Displays
• 2D/3D LCD TVs and Monitors
A
ll MPS parts are lead-free, halogen free, and adhere to the RoHS directive. Fo
r
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
VCC
COMP
EN
OSC
ADIM
ISET
MP3398A
16
1
2
5
7
6
C1
L1
VIN
GND
C2
String 1
String 2
String 3
String 4
VOUT
C3
R1
R2
VIN
15
PWM
3
R4
GATE
ISENSE
GND
OVP
LED1
LED2
LED3
LED4
D1
14
13
4
12
11
10
9
8
R3
C4
R5
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
MP3398A Rev. 1.03 www.MonolithicPower.com 2
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ORDERING INFORMATION
Part Numbe
r
Package Top Marking
MP3398AGS* SOIC16 MP3398A
MP3398AGF** TSSOP16-EP MP3398A
MP3398AGY*** SOIC20 MP3398A
* For Tape & Reel, add suffix –Z (e.g. MP3398AGS–Z);
** For Tape & Reel, add suffix –Z (e.g. MP3398AGF–Z);
*** For Tape & Reel, add suffix –Z (e.g. MP3398AGY–Z);
PACKAGE REFERENCE
14
13
12
11
16
15
7
8
TOP VIEW
10
9
3
4
5
6
1
2
LED2
LED3
LED1
VCC
VIN
GATE
IS
EN
SE
OVP
OSC
COMP
EN
LED4
PWM
ISET
GND
ADIM
OSC
LED2
COMP
LED3
EN
LED4
14
13
12
11
Exposed Pad
Connect to GND
LED1
16
15
7
8
VCC
VIN
IS E T
GND
GATE
IS
ENSE
O
VP
TOP VIEW
10
9
3
4
5
6
1
2
PWM
ADIM
18
17
16
15
20
19
7
8
TOP VIEW
14
13
3
4
5
6
1
2
OVP
LED1
NC
VCC
VIN
GATE
ISENSE
NC
GND
COMP
EN
ISET
PWM
NC
NC
OSC
9
10
LED4
ADIM
12
11
LED2
LED3
SOIC16 TSSOP16-EP SOIC20
AB SOLUTE MAXIMUM RATINGS (1)
VIN .............................................. -0.3V to +30V
VGATE ........................................... -0.3V to +6.5V
VCC ............................................ -0.3V to +6.8V
VLED1 to VLED4 .................................. -1V to +55V
VISENSE ......................................... -0.5V to +6.5V
All Other Pins ............................... –0.3V to VCC
Continuous Power Dissipation (TA = 25°C) (2)
SOIC16 .................................................... 1.56W
TSSOP16-EP………………………………2.78W
SOIC20 ………………………………… 1.74W
Junction Temperature .............................. 150°C
Lead Temperature ................................... 260°C
ESD Capability Human Body Mode (all pins)
................................................................. 3.5kV
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
Thermal Resistance (4) θJA θJC
SOIC16……………………………80……35....°C/W
TSSOP16-EP……………………45…….10….°C/W
SOIC20 ……………………72 ...... 30 ... °C/W
Notes:
1) Exceeding these ratings may damage the device. The voltage
is measured with a 20MHz bandwidth limited oscilloscope.
2) The maximum allowable power dissipation is a function of the
maximum junction temperature TJ (MAX), the junction-to-
ambient thermal resistance JA, and the ambient temperature
TA. The maximum allowable continuous power dissipation a
t
any ambient temperature is calculated by PD (MAX) = (TJ
(MAX)-TA)/JA. 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 permanen
t
damage.
3) The device is not guaranteed to function outside of its
operating conditions.
4) Measured on JESD51-7, 4-layer PCB.
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
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ELECTRICAL CHAR ACTERISTICS (5)
VIN =12V, VEN = 5V, TA = 25°C, unless otherwise noted.
Parameters Symbol Condition Min Typ Max Units
Operating Input Voltage VIN 5 28 V
Supply Current (Quiescent) IQ VIN=12V, VEN=5V, no load
without switching 1.2 1.35 1,5 mA
Supply Current (Operation) IOP VIN=12V, VEN=5V, no load
with switching 3 5.5 mA
Supply Current (Shutdown) IST V
EN=0V, VIN=12V 0.01 0.5 A
LDO Output Voltage VCC VEN=5V, 7V<VIN<28V,
0<IVCC<10mA 5.4 6 6.6 V
VCC UVLO Threshold VIN_UVLO Rising Edge 3.6 4 4.4 V
VCC UVLO Hysteresis 200 mV
EN High Voltage VEN_HIGH VEN Rising 1.8 V
EN Low Voltage VEN_LOW V
EN Falling 0.6 V
STEP-UP CO NV ERT ER
Gate Driver Impedance
(Sourcing) V
CC=6V,VGATE=6V 4.5 7
Gate Driver Impedance
(Sinking) V
CC=6V,IGATE=10mA 2.5 5
Switching Frequency fSW ROSC= 115k 459 540 621 kHz
ROSC= 374k 150 180 210 kHz
OSC Voltage VOSC 1.20 1.23 1.26 V
Maximum Duty Cycle DMAX 93 %
Cycle By Cycle ISENSE
Current Limit Max Duty Cycle 145 180 215 mV
COMP Source Current Limit ICOMP SOLI 1V<COMP<1.9V 70 A
COMP Sink Current Limit ICOMP SILI 1V<COMP<1.9V 17 A
COMP Trans-conductance GCOMP ICOMP=±10A 400 A/V
CURRENT DIMMING
PWM Input Low Threshold VPWM_LO V
PWM Falling 0.75 V
PWM Input High Threshold VPWM_HI V
PWM Rising 1.25 V
Analog Dimming Input Low
Threshold Adim_L RISET=9.72k 0.38 0.41 0.44 V
Analog Dimming Input High
Threshold Adim_H 1.44 1.49 1.54 V
LED CURRENT REGULATION
ISET Voltage VISET 1.195 1.22 1.245 V
LEDX Average Current ILED R
ISET=30.5k 31.3 32.3 33.3 mA
Current Matching (5) I
LED=33.2mA 2.5 %
VCC Max Current Limit Icc_Limit 50 75 100 mA
LED FET Resistance R_LED ILED=10mA 1.7
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
MP3398A Rev. 1.03 www.MonolithicPower.com 4
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ELECTRICAL CHAR ACTERISTICS (continued)
VIN =12V, VEN = 5V, TA = 25°C, unless otherwise noted.
Parameters Symbol Condition Min Typ Max Units
LEDX Regulation Voltage VLEDX ILED=330mA 800 mV
ILED=60mA 285 mV
PROTECTION
OVP(Over Voltage Protection)
Threshold VOVP_OV Rising Edge 1.20 1.23 1.26 V
OVP(Over Voltage Protection)
Threshold HYS VOVP_HYS HYS 80 mV
OVP UVLO threshold VOVP UV Step-up Converter Fails 30 75 120 mV
LEDX UVLO Threshold VLEDX_UV 120 200 280 mV
LEDX Over Voltage Threshold VLEDX_OV 5.8 6.3 6.8 V
LED Short Fault Cycles T_LED_OV 4096
Latch-Off Current Limit VLMT 560 640 720 mV
Thermal Protection Threshold TST 150 °C
Thermal Protection Hysteresis 25 °C
Notes:
5) Matching is defined as the difference of the maximum to minimum current divided by 2 times average currents.
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
MP3398A Rev. 1.03 www.MonolithicPower.com 5
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TYPICAL CHARACTERIS TICS
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
MP3398A Rev. 1.03 www.MonolithicPower.com 6
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TYPICAL PERFORMANCE CHARAC TERISTICS
VIN = 12V, VOUT = 30V, L = 33µH, ILED=120mA/String, 4 strings, TA = 25°C, unless otherwise noted.
80
82
84
86
88
90
92
94
96
98
0 5 10 15 20 25 30
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
MP3398A Rev. 1.03 www.MonolithicPower.com 7
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TYPICAL PERFORMANCE CHARAC TERISTICS (continued)
VIN = 12V, VOUT = 30V, L = 33µH, TA = 25°C, unless otherwise noted.
VSW
20V/div.
VOUT
20V/div.
IL
1A/div.
ILED
500mA/div.
VSW
20V/div.
VADIM
2V/div.
IL
1A/div.
ILED
200mA/div.
VSW
20V/div.
VLED1
20V/div.
IL
1A/div.
ILED
500mA/div.
VSW
20V/div.
VSENSE
500mV/div.
IL
10A/div.
ILED
1A/div.
VSW
20V/div.
VCOMP
1V/div.
IL
5A/div.
ILED
500mA/div.
VSW
20V/div.
VPWM1
5V/div.
IL
1A/div.
ILED
500mA/div.
VSW
20V/div.
VOUT
20V/div.
IL
1A/div.
ILED
500mA/div.
VSW
20V/div.
VOUT
10V/div.
IL
1A/div.
ILED
500mA/div.
VSW
20V/div.
VEN
5V/div.
IL
1A/div.
ILED
500mA/div.
Steady State VIN Power On EN Power On
Short Inductor Protection Short Diode Protection
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
MP3398A Rev. 1.03 www.MonolithicPower.com 8
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PIN FUNCTIO NS
TSSOP16-EP
&SOIC16
Pin #
SOIC20
Pin # Name Description
1 1 COMP
Step-up Converter Compensation Pin. This pin compensates the regulation
control loop. Connect a ceramic capacitor from COMP to GND.
2 2 EN
Enable Control Input. A voltage greater than 1.8V will turn the part on and less
than 0.6 V will turn the part off. Do not let this pin float.
3 3 PWM
Input Signal for PWM Brightness Control. By applying a PWM signal on this
pin, the LED current can be chopped and the average current is equal to
Iset*D_dim (I_set is the LED current value set by a resistor connected to PIN
6; D_dim is the duty cycle of the PWM dimming duty cycle). Make sure the
PWM amplitude voltage level > VPWM_HI and the low level voltage < VPWM_HI.
The input PWM signal frequency mainly determines the LED current dimming
ratio. Lower dimming frequency, smaller dimming current can be gotten. In
general, 200Hz to 2kHz can be used to cover most of the customers’ LED
current dimming requests. Internally weakly pulled to GND if this pin is floated.
If PWM dimming is not required, pulling this pin to high
voltage(1.25V<Vpwm<5V),
4 5 GND Ground.
5 7 OSC
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.
6 8 ISET
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
1.225V. The LED current is proportional to the current through the ISET
resistor.
7 9 ADIM
Signal Input for Analog Brightness Control. The LED current amplitude is
determined by this pin and the input signal can be either a PWM signal or a
DC voltage signal. An internal RC filter (10Mohm resistor and 100pF
capacitor) is integrated to this pin. So, if a PWM signal applied to this
pin, >20kHz frequency is recommended to get a better PWM signal filtering
performance and make sure the amplitude voltage is higher than 1.5V and low
level voltage is less than 0.4V. For DC signal input, please apply a DC input
signal range from 0.4V to 1.5V to linearly set the LED current from 0% to
100%. Internally weakly pulled to GND if this pin is floated. If Analog dimming
is not required, pulling this pin to high voltage(1.54V<Vpwm<5V),
8 10 LED4
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.
9 11 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.
10 12 LED2
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.
11 13 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.
12 14 OVP
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
MP3398A triggers Over Voltage Protection mode.
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
MP3398A Rev. 1.03 www.MonolithicPower.com 9
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PIN FUNCTIONS (continued)
TSSOP16-EP
&SOIC16
Pin #
SOIC20
Pin # Name Description
13 17 ISENSE
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.
14 18 GATE
Step-up Converter Power Switch Gate Output. This pin drives the external
power N-MOS device.
15 19 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.
16 20 VCC
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.
4, 6,
15, 16 NC No Connect.
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
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BLOCK DIAGR AM
Control
Logic
+
-
Current Sense
Amplifier
+
-
PWM
Comparator
Oscillator
+
-1.23 V
OV
Comparator
+
-
+
-
LED1
+
-
1.225V
Max
Min
Feedback
Control
6.3V
EA
Short String
Protection
Regulator
LED4
OVP
ISENSE
GND
VIN
VCC
PWM
ADIM
ISET
COMP
OSC
EN Enable
Control
Ref
GATE
Current Control
100ns
Blanking
+
-
ILIMIT
+
-
UP_CLAMP
PWM
STOP
200 ns
Blank Time
Figure 1—Functional Block Diagram
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
MP3398A Rev. 1.03 www.MonolithicPower.com 11
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OPERATION
The MP3398A is a step-up converter with peak-
current mode. It employs 4 channels of current
sources to drive up to 4 strings of white LEDs.
Internal 6V Regulator
The MP3398A 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 MP3398A
features under-voltage lockout (UVLO). The
chip is disabled until VCC exceeds the UVLO
threshold. The UVLO hysteresis is
approximately 200mV.
System Startup
When enabled, the MP3398A 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 75mV will disable the chip. The
MP3398A also checks other safety limits,
including UVLO and over-temperature
protection (OTP), over-current protection 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.
It is recommended that the enable signal occurs
after the establishment of the input voltage and
PWM dimming signal during the start-up
sequence to avoid large inrush current.
Step-Up Converter
The converter operating frequency is
programmable (from 100kHz to 500kHz) with a
external resistor connected to the OSC pin.
This helps to optimize the size of external
components and the efficiency.
At the beginning of each switching cycle, the
internal clock turns on the external MOSFET (In
normal operation, the minimum turn on time is
200ns). 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
reaches the output voltage of the error amplifier
(VCOMP) the external MOSFET turns off.
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.
If the feedback voltage drops below the
reference, the output of the error amplifier
increases. This results 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, especially in the
case of VOUT ≈ VIN, the converter runs in
pulse-skipping mode where the MOSFET turns
on for a minimum on-time of approximately
200ns, 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.
Dimming Contr ol
The MP3398A provides two dimming methods:
PWM or analog dimming mode.
For PWM dimming, apply a PWM signal to
PWM pin. The LED current is chopped by this
PWM signal and the average LED current is
equal to Iset*D_dim where D_dim is the duty
cycle of PWM dimming signal and Iset is the
LED current amplitude.
For analog dimming, either a PWM signal or DC
signal can be applied to ADIM pin.
When a PWM signal is applied to ADIM pin, this
signal will be filtered by the internal RC filter.
The LED current amplitude is equal to
Iset*D_Dim where D_dim is the duty cycle of
PWM dimming signal and Iset is the LED
current amplitude. 20KHz or higher PWM signal
is recommended to get the better filtering
performance.
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
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When a DC signal is applied to ADIM pin, the
voltage range in 0.4V to 1.5V directly sets the
LED current linearly from 0% to 100%.
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. If the
OVP point has been triggered for >4us, the chip
stops switching and marks the strings which
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.
The MP3398A will always attempt to light at
least one string. If all strings are open, the
MP3398A shuts down the step-up converter.
The strings will remain in this marked state until
the chip reset.
Short String Protection
The MP3398A monitors the LEDX pin voltages
to determine if a short string fault has occurred.
If one or more strings are shorted, the
respective LEDX pins tolerate high voltage
stress. If an LEDX pin voltage is higher than
6.3V, this condition triggers the detection of a
short string. When a short string faults (LEDX
over-voltage fault) keeps for 4096 switching
clocks, 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. In order to prevent mis-triggering
short LED protection when open LED string or
sharp ADIM, the short LED protection function
is disabled when Vledx of all used LED
channels are higher than 1.5V.
Inductor/Di ode short Protection
To prevent the IC and external MOSFET
damage when external inductor is shorted,
MP3398A has the protection mode in two
following methods. When inductor is shorted,
the output can not maintain enough energy to
load the LED and the output voltage will drop.
Thus, the COMP (the error amplifier output)
voltage tends to rise till be clamped high, when
it lasts longer than 512 switching cycles the IC
turns off and latches. In some cases that the
COMP voltage can not be clamped to high
when inductor is shorted, the IC also provides
the protection mode by detecting the current
flowing through power MOSFET. In this mode,
when the current sense voltage across sense
resistor (connected between MOSFET and
GND) hits VLMT limit value and lasts for 4
switching cycles, the IC turns off and latches.
Thermal Shutdown Protection
To prevent the IC operate at exceedingly high
temperature, thermal shutdown is implemented
in this chip by detecting the silicon die
temperature. When the die temperature
exceeds the upper threshold TST, the IC
shutdowns and recovers to normal operation
when die temperature drops below lower
threshold. Typically, the hysteresis value is
25°C.
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
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APPLICATION INFORMATION
Selecting the Switching Frequency
The switching frequency of the step-up converter
is recommended from 100kHz to 500kHz for
most of application. An oscillator resistor on OSC
pin sets the internal oscillator frequency for the
step-up converter according to the below
equation:
SW
OSC
67320
F(kHz) R(k)
=
Ω
For ROSC=374k, the switching frequency is set
to 180kHz.
Setting the LED Current
The LED each string current can be set through
the current setting resistor on the ISET pin.
LED
810 1.22V
I(mA) Rk
ISET
×
=
For RSET=8.2k, the LED current is set to
120mA. Please do not leave ISET pin open.
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
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 4.7F ceramic capacitor
in parallel with a 220µF electrolytic capacitor.
Selecting the Inductor and Current Sensing
Resistor
The MP3398A 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 N-
channel MOSFET. However, the larger value
inductor has a larger physical size, higher series
resistance, and lower saturation current.
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
with high efficiency and good EMI performance.
Calculate the required inductance value using the
equation:
2
OUT
SW LOAD
V D(1D)
L 2 f I
×××−
≥
××
IN
OUT
V
D1 V
=−
Where VIN and VOUT are the input and output
voltages, fSW is the switching frequency, ILOAD is
the LED load current, and is the efficiency.
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
the worst-case current-limit voltage, VSENSE.
SENSE
L(PEAK)
0.8 VSENSE
RI
×
=
OUT LOAD IN OUT IN
L(PEAK)
IN SW OUT
VI V(V V)
IV2LFV
××−
=+
×× ×
Where IL(PEAK) is the peak value of the inductor
current. VSENSE is shown in Figure 2.
V
SENSE
(mV)
Vsense vs.Duty Cycle
0
50
100
150
200
250
300
350
400
450
0102030405060708090100
Figure 2—VSENSE vs Duty Cycle
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
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Selecti ng the Power MOSFET
The MP3398A 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
5. Total gate charge, QG
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.
The maximum current through the power
MOSFET occurs at the minimum input voltage
and the maximum output power. The maximum
RMS current through the MOSFET is given by
RMS(MAX) IN(MAX) MAX
IID=× , where:
OUT IN(MIN)
MAX
OUT
VV
DV
−
≈
The current rating of the MOSFET should be
greater than 1.5xIRMS
The ON resistance of the MOSFET determines
the conduction loss, which is given by:
kRIP (on) DS
2
RMScond ××=
Where k is the temperature coefficient of the
MOSFET.
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.
SWINDS
PLTDR
GGD
SWINDS
THDR
GGS1
SW
fIV
VV
RQ
fIV
VV
RQ
P
×××
−
×
+×××
−
×
=
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.
The total gate charge, QG, is used to calculate
the gate drive loss. The expression is
SWDRGDR fVQP ××=
Where VDR is the drive voltage.
Selecting the Output Capacitor
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
4.7F ceramic capacitor in parallel with a 22F
electrolytic capacitor will suffice.
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, the protection will
be triggered.
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.
HIGH
OVP
LOW
R
V1.23(1 )
R
=×+
Selecting Dimming Control Mode
The MP3398A provides two different dimming
methods.
1. Direct PWM Dimming
An external PWM dimming signal is employed to
achieve PWM dimming control. Apply a PWM
dimming signal (in the range of 100Hz to 20kHz)
to the PWM pin. The minimum recommended
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
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amplitude of the PWM signal is 1.5V and the low
level should be less than 0.4V.
Table 1—The Range of PWM Dimmi ng Duty
f
PWM(Hz) Dmin D
max
100<f≤200 0.30% 100%
200<f≤500 0.75% 100%
500<f≤1k 1.50% 100%
1k<f≤2k 3.00% 100%
2k<f≤5k 7.50% 100%
5k<f≤10k 15.00% 100%
10k<f≤20k 30.00% 100%
2. Analog Dimming
For analog dimming, apply a PWM signal or a
DC voltage signal to ADIM pin. An internal RC
filter (10Mohm resistor and 100pF capacitor) is
integrated to this pin. So, if a PWM signal applied
to this pin, >20kHz frequency is recommended to
get a better PWM signal filtering performance
and make sure the amplitude voltage is higher
than 1.5V and low level voltage is less than 0.4V
with >15mV/ns slope rate for falling/rising edge.
For DC signal input, please apply a DC input
signal range from 0.4V to 1.5V to linearly set the
LED current from 0% to 100%.
Expanding LED Channels
The MP3398A can expand the number of LED
channels by using two or three MP3398A in
parallel. To connect two MP3398A 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.
Layout Considerations
The circuit layout for the MP3398A 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 3).
Figure 3—Layout Consideration
All logic signals refer to the signal ground. in
order to reduce the noise affection, it is
recommend to separate the power ground(PGND)
and signal ground(GND), then connect PGND
and GND together.
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
MP3398A Rev. 1.03 www.MonolithicPower.com 16
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TYPICAL APPLICATION CIRCUITS
10
R3
NC
R1
0
R9
VIN
GND
EN
PWM-DIM
0V
C4
NC
C5 C1
F1 L1
B360
D1
NC
C7
00V
C2
C6
00V
C3
357k
R2
10k
R4
100pF
C8
LED
LED1
LED2
LED3
LED4
0
R12
0
R13
0
R15
10
R5
M1
100V/4A
2k
R16
100k
R18
100pF
100k
R14
330k
R10
2k
R8
100k
R11
C9
270
R7
470nF
C10
0.05
R6
8V-28V
12S 4P 120mA/string
NC
C11
R17
8.45k
NC
C13
0
R19
NC
C14
ISET
6
PWM
3
OSC
5
EN
2
COMP
1
VCC
16
VIN
15
LED4 8
LED3 9
LED2 10
LED1 11
OVP 12
GND 4
ISENSE 13
GATE 14
ADIM
7
U1
MP3398AGS
2k
R20
A-DIM
2k
R21
100pF
C15
C12
Figure 4: 4 string, 12 LED in series, 120mA/string application
(Some components are reasonably adjustable based on real case)
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
MP3398A Rev. 1.03 www.MonolithicPower.com 17
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© 2015 MPS. All Rights Reserved.
PACKAGE INFOR MAT ION
SOIC16
0.016(0.41)
0.050(1.27)
0
o
-8
o
DETAIL "A"
0.010(0.25)
0.020(0.50) x 45
o
SEE DETAIL "A"
0.0075(0.19)
0.0098(0.25)
0.150
(3.80)
0.157
(4.00)
PIN 1 ID
0.050(1.27)
BSC
0.013(0.33)
0.020(0.51)
SEATING PLANE
0.004(0.10)
0.010(0.25)
0.386( 9.80)
0.394(10.00)
0.053(1.35)
0.069(1.75)
TOP VIEW
FRONT VIEW
0.228
(5.80)
0.244
(6.20)
SIDE VIEW
18
16 9
RECOMMENDED LAND PATTERN
0.213
(5.40)
0.063
(1.60)
0.050(1.27)0.024(0.61)
NOTE:
1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN
BRACKET IS IN MILLIMETERS.
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.
0.010(0.25) BSC
GAUGE PLANE
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
MP3398A Rev. 1.03 www.MonolithicPower.com 18
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© 2015 MPS. All Rights Reserved.
TSSOP16-EP（with externa l thermal pad）
FRONT VIEW SID E VIE W
BOT T O M VIEW
DETAIL " A"
NOTE:
1) ALL DIM ENSI ONS ARE I N M IL L IMETERS.
2) PACKAGE LENGT H DOES NOT I NCL UDE MO LD
FLASH, PROT RUSIO N O R GAT E BURR.
3) PACKAGE WIT DH DOES NOT INCL UDE I NT ERLEAD
FLASH O R PROT RUSI O N.
4) LEAD CO PL ANARITY (BOT T OM OF L EADS AFT ER
FO RMI NG) SHALL BE 0.10 MIL L IM ETERS M AX.
5) DRAW I NG CONF O RM S TO JEDEC M O-153,
VARIATI ON ABT.
6) DRAWI NG IS NOT T O SCALE.
PIN 1 ID
TOP VIEW RECOMMENDED LAND PATTERN
SEE DETAI L "A"
STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER
NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications.
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.
MP3398A Rev. 1.03 www.MonolithicPower.com 19
5/27/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2015 MPS. All Rights Reserved.
SOIC20
NOTE:
1) CO NTROL DIMENSION IS IN INCHES. DIMENSION IN
BRACKET IS IN MILLIMETERS.
2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH,
PRO TRUSIONS OR GATE BURRS.
3) PACKAGE WIDTH DOES NOT INCLUDE INTERLE AD FLASH
OR P ROTRUSIONS.
4) LEAD COP LANARITY (BO TTOM OF LEADS AFTER FORMING)
SHALL BE 0.10 MILLIMETERS MAX.
5) DRAWING CONFO RMS TO JEDEC MS-013, VARIATION AC.
6) DRAWING IS NOT TO SCALE.
0.013(0.33)
0.020(0.51)
0.496(12.60)
0.512(13.00)
SEATING P LANE
0.050(1.27)
BSC
PIN 1 ID
0.291
(7.40)
0.299
(7.60)
0.394
(10.00)
0.418
(10.60)
110
11
20
0.093(2.35)
0.104(2.65)
0.004(0.10)
0.012(0.30)
TOP VIEW
FR ON T VI E W SID E VI EW
0.009(0.23)
0.013(0.33)
RECOMMENDED LAND PATTERN
0.370
(9.40)
0.079
(2.00)
0.024
( 0.61) 0.050
(1.27)
SEE DETAIL "A"
0.016(0.41)
0.050(1.27)
0o-8o
DET AIL " A"
0.010(0.25)
0.030(0.75) x 45o
0.010 (0.25) BSC
GAUGE PLANE
