MP3385
4-String, 80V Output
WLED Controller with I2C Interface
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP3385 is a step-up controller with 4
regulated current channels designed to drive
WLED arrays for middle and large-size LCD
panel backlighting applications.
The MP3385 uses peak current mode, PWM
control architecture for system loop regulation.
It drives an external MOSFET to boost up the
output voltage from a 4.5V to 33V input supply.
It employs an I2C digital interface and can
flexibly set the operation and protection modes,
including dimming mode, dimming current and
dimming ratio, OCP, OVP, LED short protection
threshold, and the switching frequency. For
easy application use and board debugging, the
MP3385 detects and automatically disables the
unused LED strings during start-up to avoid
charging the output to the OVP threshold.
The MP3385 achieves 1.8% current matching
between each string. The low regulation voltage
on the LED current sources improves efficiency
and reduces power loss in order to achieve a
higher current output.
The MP3385 supports analog, PWM, and
combined analog and PWM dimming modes to
meet different application requirements. Full
protection features include OCP, OTP, UVP,
OVP, LED short/open protection, and
inductor/diode short protection.
The MP3385 is available in a QNF-20
(4mm x 4mm) and a TSSOP20-EP package.
4-String, Max 300mA/String WLED Driver
4.5V to 33V Input Voltage Range
80V Abs. Rating for Each String
1.8% Current Matching Accuracy for Each
String
Unused Channel Auto-Detection Function
during Start-Up
100kHz-900kHz Programmable Switching
Frequency
Multiple Dimming Modes Selected by I2C
Interface:
1. Direct PWM Dimming Mode
2. Internal Fixed 23kHz PWM Dimming
Mode
3. Analog Dimming Mode by Input Pulse
4. Internal Analog Dimming Mode
5. Mixed Dimming Mode by Input Pulse
6. Internal Mixed Dimming Mode
2%-100% Programmable Full Scale Current
with 8-Bit Resolution
0%-100% LED Dimming Range with 10-Bit
Resolution for Internal Dimming Mode
Cascading Capability with a Single Power
Source
18V to 80V Over-Voltage Protection,
2V/Step
0.15V to 0.5V Latch-Off/Recoverable OCP
Protection Threshold, 50mV/Step
Recoverable Thermal Shutdown Protection
APPLICATIONS
Desktop LCD Flat Panel Displays
All-in-One
2D/3D LCD TV
All MPS parts are lead-free, halogen-free, and adhere to the RoHS directive. For
MPS green status, please visit the MPS website under Quality Assurance.
“MPS” and “The Future of Analog IC Technology” are registered trademarks of
Monolithic Power Systems, Inc.
MP3385 Rev. 1.02
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
TYPICAL APPLICATION
MP3385 Rev. 1.02
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
ORDERING INFORMATION
Part Number
MP3385GR*
MP3385GF**
Package
QFN-20 (4mm x 4mm)
TSSOP20-EP
Top Marking
See Below
See Below
* For Tape & Reel, add suffix –Z (e.g. MP3385GR–Z)
** For Tape & Reel, add suffix –Z (e.g. MP3385GF–Z)
TOP MARKING (QFN-20 (4mm x 4mm))
MPS: MPS prefix
Y: Year code
WW: Week code
MP3385: Part number
LLLLLL: Lot number
TOP MARKING (TSSOP20-EP)
MPS: MPS prefix
YY: Year code
WW: Week code
MP3385: Part number
LLLLLLLLL: Lot number
PACKAGE REFERENCE
DRV
1
15
VCC
2
14 LED3
EN
3
VIN
4
12
PWM
5
11 COMP
Exposed Pad
Connect to GND
PGND
13 LED4
ISET
QFN-20 (4mm x 4mm)
MP3385 Rev. 1.02
8/29/2017
TSSOP20-EP
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
ABSOLUTE MAXIMUM RATINGS (1)
VIN .................................................-0.3V to +40V
VOVP, VLED1 to VLED4 .......................-0.3V to +80V
All other pins ................................-0.3V to +6.5V
(2)
Continuous power dissipation (TA = 25°C)
QFN-20 4mm x 4mm ............................... 2.97W
TSSOP20-EP………………………….…...3.12W
Junction temperature ................................150°C
Lead temperature .....................................260°C
Recommended Operating Conditions
(3)
Supply voltage (VIN) ......................... 4.5V to 33V
Operating junction temp. .......... -40°C to +125°C
MP3385 Rev. 1.02
8/29/2017
Thermal Resistance
(4)
θJA
θJC
QFN-20 (4mm x 4mm)………....42........9…..°C/W
TSSOP20-EP……… …………..40….….8….°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 produce an excessive die temperature,
causing the regulator to 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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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
ELECTRICAL CHARACTERISTICS
VIN = 12V, VEN = 5V, TA = 25°C, unless otherwise noted.
Parameters
Symbol
Condition
Operating input voltage
VIN
Supply current (quiescent)
IQ
VIN = 12V, no switching
Supply current (shutdown)
IST
LDO output voltage
VCC
VEN = 0V, VIN = 12V,
7V < VIN < 28V,
0 < IVCC < 10mA
Rising edge
VCC UVLO threshold
VIN_UVLO
Min
4.5
VEN_HIGH
VEN rising
EN low voltage
VEN_LOW
VEN falling
Step-Up Converter
Gate driver sourcing
impedance
Gate driver sinking
impedance
fSW
OSC voltage
VOSC
Maximum duty cycle
DMAX
Cycle-by-cycle ISENSE
current limit
COMP sink current limit
COMP trans-conductance
Unit
33
V
mA
1
μA
5.4
6
6.3
V
3.7
4
4.3
V
340
EN high voltage
COMP source current limit
Max
3
VCC UVLO hysteresis
Switching frequency
Typ
mV
1.5
V
0.6
V
VCC = 6V, VGATE = 6V
4
Ω
VCC = 6V, IGATE = 10mA
2
Ω
Fsw = 0010b, ROSC = 100kΩ
156
195
234
kHz
Fsw = 1001b, ROSC = 100kΩ
672
820
967
kHz
ROSC = 100kΩ, fSW = 900kHz
1.75
1.79
1.83
V
90
%
OCP = 000b
130
150
170
mV
OCP = 111b
465
500
535
mV
ICOMP SOLI
1V < COMP < 2.9V
75
μA
ICOMP SILI
1V < COMP < 2.9V
15
μA
∆ICOMP = ±10µA
100
μA/V
GCOMP
Current Dimming
PWM input low threshold
VPWM_LO
VPWM falling
PWM input high threshold
VPWM_HI
VPWM rising
Dimming transfer point
0.4
1.5
V
MODE = 10b
25
%
MODE = 11b
50
%
23
kHz
Dimming resolution
0.098
%
DIM = 1111111111b
100
%
Internal dimming frequency
20
Dimming ratio
V
Current Regulation
ISET voltage
VISET
LEDX average current
ILED
Full scale current
RISET = 100.8kΩ, ILED=FFh
ILED = 00h
ILED = FFh(5)
1.93
1.98
2.03
V
192
201
212
mA
2
%
100
%
NOTE:
5) Guaranteed by design.
MP3385 Rev. 1.02
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
ELECTRICAL CHARACTERISTICS (continued)
VIN = 12V, VEN = 5V, TA = 25°C, unless otherwise noted.
Parameters
Symbol
Current matching
(6)
LEDX regulation voltage
Condition
Min
Typ
ILED = 200mA
VLEDX
Max
Unit
1.8
%
ILED = 330mA
820
mV
ILED = 200mA
700
mV
ILED = 60mA
500
mV
Protection
OVP protection threshold
VOVP_OV
OVP UVLO threshold
VOVP_UV
LEDX UVLO threshold
VLEDX_UV
LEDX over-voltage threshold
VLEDX_OV
Thermal protection threshold
OVP = 00000b
16.8
18
18.9
V
OVP = 11100b
71.5
74
75.5
V
Step-up converter fails
2.5
147
206
V
265
mV
LEDS = 000b
4
V
LEDS = 111b
11
V
150
°C
25
°C
TST
Thermal protection hysteresis
2
I C Interface Specifications
Input logic low
VIL
Input logic high
VIH
Output logic low
VOL
SCL clock frequency
fSCL
SCL high time
tHIGH
0.6
μs
SCL low time
tLOW
1.3
μs
Data setup time
tSU,DAT
100
ns
Data hold time
tHD,DAT
0
Setup time for repeated start
tSU,STA
0.6
μs
Hold time for start
Bus-free time between a start
and stop condition
Setup time for stop condition
tHD,STA
0.6
μs
tBUF
1.3
μs
tSU,STO
0.6
20+0.
1×CB
20+0.
1 ×CB
μs
300
ns
300
ns
0
50
ns
400
pF
Rise time of SCL and SDA
tR
Fall time of SCL and SDA
tF
Pulse width of suppressed
spike
Capacitance bus for each bus
line
tSP
0.4
1.3
ILOAD = 3mA
CB
V
V
0.4
V
400
kHz
0.9
μs
NOTE:
6) Matching is defined as the difference between the maximum to minimum current divided by 2x the average currents.
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
Figure 1: I2C Compatible Interface Timing Diagram
MP3385 Rev. 1.02
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
TYPICAL PERFORMANCE CHARACTREISTICS
VIN = 12V, VEN = 3.3V, unless otherwise noted.
MP3385 Rev. 1.02
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
TYPICAL PERFORMANCE CHARACTREISTICS
VIN = 12V, VEN = 3.3V, L = 33µH, 120mA/string, 4-string, 14 LEDs, TA = 25°C, unless otherwise
noted.
VSW
20V/div.
VOUT
50V/div.
VSW
20V/div.
VSW
20V/div.
VOUT
20V/div.
VOUT
20V/div.
VEN
5V/div.
VIN
10V/div.
IL
1A/div.
ILED
500mA/div.
IL
50mA/div.
ILED
50mA/div.
VSW
20V/div.
VSW
20V/div.
VSW
20V/div.
VPWM
5V/div.
VOUT
20V/div.
IL
2A/div.
VOUT
20V/div.
VOUT
20V/div.
VPWM
5V/div.
ILED
200mA/div.
ILED
200mA/div.
ILED
200mA/div.
VSW
20V/div.
VOUT
20V/div.
IL
1A/div.
VSW
20V/div.
VOUT
20V/div.
VPWM
5V/div.
VSW
20V/div.
ILED
200mA/div.
ILED
200mA/div.
ILED
200mA/div.
MP3385 Rev. 1.02
8/29/2017
VPWM
5V/div.
VOUT
20V/div.
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
TYPICAL PERFORMANCE CHARACTREISTICS (continued)
VIN = 12V, VEN = 3.3V, 120mA/string, 4-string, 14 LEDs, TA = 25°C, unless otherwise noted.
MP3385 Rev. 1.02
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
PIN FUNCTIONS
Package
Pin #
Name
1
DRV
2
VCC
3
EN
4
VIN
5
PWM
6
7
SCL
SDA
8
FT
9
LPF
10
11
12
13
14
15
16
17
18
19
20
Description
Step-up converter power switch gate output. DRV drives the external power N-MOSFET
device. It is recommended to connect a resistor (e.g.,10Ω) to DRV
Internal 6V linear regulator output. VCC provides the power supply for the external
MOSFET switch gate driver and the internal control circuitry. Bypass VCC to GND with a
ceramic capacitor.
Enable control input. A voltage greater than 1.5V turns the part on. A voltage less than
0.6V turns the part off. Do NOT float EN.
Supply input. VIN must be bypassed locally.
PWM input signal for brightness control. Make sure the PWM amplitude voltage
level > VPWM_HI, and the low-level voltage < VPWM_LO. Mainly, the input PWM signal
frequency determines the LED current dimming ratio when the part works in direct PWM
dimming mode. For analog and mixed dimming, the PWM pulse is filtered to a DC by an LPF
capacitor, and the LED current is proportional to the input PWM duty. If PWM is floated,
internally pull PWM to GND weakly.
I2C clock input.
I2C data input.
Fault indication output. FT is an open drain during normal operation. It is pulled low during
a fault condition.
Low pass filter output for analog dimming with PWM input. A capacitor is connected
between LPF and GND when the part operates in external PWM input analog dimming or
mixed dimming. Remove the LPF capacitor when the part operates in direct PWM dimming
mode.
Switching frequency set. Connect a resistor (Rosc) between OSC and GND to set the stepup converter switching frequency. The clock frequency is proportional to the current sourced
OSC
from OSC. There is a 100~900kHz switching frequency selected by the I2C interface when
connected to a 100kΩ resistor at OSC.
Step-up converter compensation. COMP compensates the regulation control loop.
COMP
Connect a ceramic capacitor and resistor from COMP to GND.
LED current set. Tie a current-setting resistor from ISET to ground to program the current in
ISET
each LED string.
LED string 4 current input. LED4 is the open-drain output of an internal dimming control
LED4
switch. Connect the LED string 4 cathode to LED4.
LED string 3 current input. LED3 is the open-drain output of an internal dimming control
LED3
switch. Connect the LED string 3 cathode to LED3.
PGND Power ground.
LED string 2 current input. LED2 is the open-drain output of an internal dimming control
LED2
switch. Connect the LED string 2 cathode to LED2.
LED string 1 current input. LED1 is the open-drain output of an internal dimming control
LED1
switch. Connect the LED string 1 cathode to LED1.
OVP Output over-voltage protection.
Current sense input. During normal operation, IS senses the voltage across the external
inductor current-sensing resistor (RSENSE) for peak-current–mode control. Also, it limits the
IS
inductor current during every switching cycle. If the MP3385 is used for cascading
applications, IS of the slave chip should be tied to GND. Do NOT float IS.
AGND Signal ground.
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
FUNCTIONAL BLOCK DIAGRAM
Figure 2: MP3385 Block Diagram
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
OPERATION
The MP3385 employs a programmable
constant frequency, peak current mode step-up
converter with 4 regulated current channels to
drive an array of 4 strings of white LEDs. It has
an I2C interface for easy communication that
flexibly sets the operation modes.
Internal 6V Regulator
The MP3385 includes an internal linear
regulator (VCC). When VIN is greater than 6.5V,
the 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 MP3385
features under-voltage lockout (UVLO). The
chip is disabled until VCC exceeds the UVLO
threshold.
The
UVLO
hysteresis
is
approximately 340mV.
System Start-Up
When enabled, the MP3385 checks the
topology connection first. The chip monitors the
over-voltage protection (OVP) pin to see if the
Schottky diode is connected or if the boost
output is shorted to GND. An OVP voltage
higher than 2.5V allows the chip to switch
normally. Otherwise, the switching is disabled.
The MP3385 checks additional safety limits
including LED open/short protection, UVLO,
over-temperature protection (OTP), and overcurrent protection (OCP) after passing the OVP
test. If all the protection tests pass, the chip
starts boosting the step-up converter with an
internal soft start.
Step-Up Converter
At the beginning of each switching cycle, the
internal clock turns on the external MOSFET.
(In normal operation, the minimum turn-on time
is around 150ns.) A stabilizing ramp is added to
the output of the current sense amplifier to
prevent sub-harmonic oscillations for duty
cycles greater than 50%. This result is fed into
the PWM comparator. When the summed
voltage reaches the output voltage of the error
amplifier (VCOMP), the external MOSFET turns
off.
the reference voltage and the feedback voltage.
Automatically, the converter chooses the lowest
active LEDX 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 pulseskipping mode where the MOSFET turns on for
a minimum on time, 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 Control
The MP3385 provides flexible dimming
methods according to the dimming mode
settings below.
1) PWM Dimming Mode:
MODE bits = 00. The LED current duty cycle
directly follows the PWM input signal duty cycle
when INTERFACE = 0. The IC works in internal
PWM dimming mode, and the LED current duty
cycle is set by the internal registers 03H and
04H when INTERFACE = 1. The internal
dimming frequency is fixed at 23kHz.
2) Analog Dimming Mode:
MODE bits = 01. The LED current amplitude
follows the duty cycle of the input PWM signal
when INTERFACE = 0. The IC works in internal
analog dimming mode (the LED current
amplitude follows the internal register value of
03H and 04H) if INTERFACE = 1.
3) Mixed Dimming Mode:
There are two transfer points from analog to
PWM dimming (25% or 50%) set by the I2C
interface.
The output voltage of the internal error amplifier
is an amplified signal of the difference between
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
If MODE bits are set to 10 (when the dimming
duty cycle is larger than the 25% threshold), the
IC works in analog dimming mode. Otherwise,
the IC works in PWM dimming mode, and the
LED current follows the PWM ratio. If MODE
bits are set to 11 (when the dimming duty cycle
is larger than the 50% threshold), the IC works
in analog dimming mode. Otherwise, the IC
works in PWM dimming mode.
In mixed dimming mode (when INTERFACE is
set to 0), the LED current amplitude is
proportional to the ratio of the external PWM
signal if the duty cycle of PWM is larger than
the transfer point (25% or 50%). The LED
current amplitude is fixed to 100% brightness
while the LED current duty is equal to the input
PWM ratio (if the duty cycle of PWM is lower
than the transfer point). When INTERFACE is
set to 1, the LED current amplitude and the duty
cycle is set by registers 03H and 04H.
Regardless of the INTERFACE setting (1 or 0),
the LED current frequency is fixed to 23kHz in
mixed dimming mode when the duty cycle < the
transfer point (25% or 50%).
In analog and mixed dimming mode, to avoid
noise at the small dimming ratio, the IC turns off
the current sources if the current is less than
1.2% times the full scale current.
For external analog and mixed dimming mode,
the smallest pulse width of the PWM signal is
limited to 2µs to avoid noise interruption.
Operation Switching Frequency
The operation frequency of the converter can
be changed by the OSC resistor and the FS0-3
bit in register 01H. The switching frequency
covers 100kHz to 900kHz through the I2C
register bits when a 100kΩ resistor is
connected to OSC. This optimizes the size of
the external components and system efficiency.
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; the IC keeps
charging the output voltage until it reaches the
over-voltage protection (OVP) threshold. If the
OVP point has been triggered, the chip stops
switching and marks the strings which have an
MP3385 Rev. 1.02
8/29/2017
LEDX pin voltage lower than 206mV. 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 MP3385 always attempts to light at least
one string. If all strings are open, the MP3385
shuts down the step-up converter. The strings
remain in this marked state until the chip resets.
Unused LED String Auto-Detection
For the MP3385, if an LED string is open or
unused before start-up, automatically the IC
detects and marks off the open channel to
avoid the output charging to the OVP value.
This function avoids start-up failure, which is
caused by the LED short string mis-protection
due to OVP triggering. This is helpful for
application use and test board debugging. The
unused LED string auto-detection function is
disabled if the OVP point is changed by the I2C
after EN and VIN power on, and I2C is active.
In addition, the MP3385 disables the unused
LED string by disabling the corresponding
register control bit for each 4-channel current
source. In some applications, if less than 4 LED
strings are needed, the unused LED current
sources can be disabled by setting the
LED1/2/3/4 bit to 0 in register 00H.
Short-String Protection
The MP3385 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 the protection
threshold, which can be programmable by
LEDS0/1/2 bits in 01H, this condition triggers
the detection of a short-string fault. When a
short-string fault remains for longer than 10ms,
the fault string is marked off and disabled. Once
a string is marked off, it disconnects from the
output voltage loop until VIN or EN re-starts.
Cycle-by-Cycle Current Limit
To prevent the external components exceeding
the current stress rating, the IC has cycle-bycycle current limit protection. The limit value is
programmable from 150mV to 500mV by
OCP0/1/2 bits in register 05H. When the current
exceeds the current limit value, the IC latches
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
off until the power is reset or ENABLE is
toggled when operating in latch-off mode (if
OCPM = 0). The device re-starts when the
current drops below the current limit again (if
OCPM = 1).
Short Inductor/Diode Protection
When the external inductor or diode is shorted,
the IC provides protection by detecting the
current flowing through the power MOSFET.
When the current sense voltage across the
sense resistor (connected between IS and GND)
hits the current protection threshold and lasts
for 4 switching cycles, the IC stops switching
and latches.
Thermal Shutdown Protection
To prevent the IC from operating at exceedingly
high temperatures, thermal shutdown is
implemented to detect the silicon die
temperature. When the die temperature
exceeds the upper threshold (TST), the IC shuts
down. The IC resumes normal operation when
the die temperature drops below the lower
threshold. Typically, the hysteresis value is
25°C.
MP3385 Rev. 1.02
8/29/2017
Fault Flag
Indicator
Output
and
Fault
Register
FT remains in an open-drain condition when the
LED driver is operating in a normal condition. It
is connected to VCC by an external 100kΩ
resistor and pulled to logic high when there is
no fault. FT goes to logic low if a fault occurs.
Meanwhile, set the corresponding fault bit in
register 03H to 1.
I2C Interface Register Description
I2C Chip Address:
After the start condition, the I2C compatible
master sends a 7-bit address followed by
an eighth read (Read: 1) or write (Write: 0) bit.
The following bit indicates the register address
to/from which the data will be written/read (see
Figure 3).
Figure 3: The I2C Compatible Device Address
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
Register Mapping:
Add
D7
D6
D5
D4
D3
D2
D1
D0
00H
LED4
LED3
LED2
LED1
NA
INTERFACE
MODE1
MODE0
01H
OCPM
LEDS2
LEDS1
LEDS0
FS3
FS2
FS1
FS0
02H
lLED7
lLED6
lLED5
lLED4
lLED3
lLED2
ILED1
lLED0
03H
DIODEO
_F
OVP_F
OCP_F
LEDS_F
LEDO_F
OTP_F
DIM1
DIM0
04H
DIM9
DIM8
DIM7
DIM6
DIM5
DIM4
DIM3
DIM2
05H
OVP4
OVP3
OVP2
OVP1
OVP0
OCP2
OCP1
OCP0
06H
ID7
ID6
ID5
ID4
ID3
ID2
ID1
ID0
MP3385 Rev. 1.02
8/29/2017
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
Table 1: Dimming Mode Register
Addr: 0x00
Bit
Bit Name
Access
Default
Description
LED current source enable bits. LED1/2/3/4 controls the
internal LED current sources, respectively.
LED1: LED current source 1; 1 = enabled. 0 = Disabled.
7:4
LED1/2/3/4
RW
1111
LED2: LED current source 2; 1 = enabled. 0 = Disabled.
LED3: LED current source 3; 1 = enabled. 0 = Disabled.
LED4: LED current source 4; 1= enabled. 0 = Disabled
3
NA
RW
NA
NA
Dimming input interface set bit.
2
INTERFACE
RW
0
0 = Dimming control by PWM input signal.
1 = Dimming control by I2C interface.
Dimming mode setting bits.
00 = PWM mode. The LED current duty cycle directly
follows the PWM input signal duty cycle when
INTERFACE = 0. The IC works in internal PWM dimming
mode, and the LED current duty cycle is set by the
internal registers 03H and 04H when INTERFACE = 1.
The internal dimming frequency is fixed at 23kHz.
1:0
MODE
RW
00
01 = Analog dimming mode. The LED current amplitude
follows the duty cycle of the input PWM signal when
INTERFACE = 0 and follows the internal register value of
03H and 04H if INTERFACE = 1.
10 = Mixed dimming mode. When the dimming duty cycle
is larger than the 25% threshold, the IC works in analog
dimming mode. Otherwise, the IC works in PWM dimming
mode.
11 = Mixed dimming mode. When the dimming duty cycle
is larger than the 50% threshold, the IC works in analog
dimming mode. Otherwise, the IC works in PWM dimming
mode.
MP3385 Rev. 1.02
8/29/2017
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
Table 2: Operation Frequency Register
Addr: 0x01
Bit
Bit Name
Access
Default
Description
Mode selection bit for cycle-by-cycle current limit.
7
OCPM
RW
0
0 = Latch-off mode current limit.
1 = Recoverable mode current limit.
LED short protection threshold.
4:6
LEDS0-2
RW
100
000 = 4V, 001 = 5V, 111 = 11V, 1V/step. Default value is
8V.
Boost converter operation frequency set bits.
3:0
FS0-3
RW
0100
0000b = Boost converter off.
0001b-1001b is corresponding to 100kHz-900kHz,
respectively. Default frequency is 400kHz.
Table 3: LED Current Full Scale Register
Addr: 0x02
Bit
7:0
Bit Name
ILED0-7
Access
RW
Default
00111011
Description
LED current full scale set bits. The set value corresponds
to the 2%-100% external setting current value by a
resistor.
00000000b = 2%. 11111111b = 100%. 0.39% per step.
The default value is 25%.
MP3385 Rev. 1.02
8/29/2017
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
Table 4: Fault Indication Register
Addr: 0x03
Bit
Bit Name
Access
Default
7
DIODEO_F
R
0
6
OVP_F
R
0
5
OCP_F
R
0
4
LEDS_F
R
0
3
LEDO_F
R
0
2
OTP_F
R
0
1:0
DIM0-1
R/W
11
Description
Diode open fault indication bit.
1 = Fault, 0 = Normal.
Output over-voltage fault indication bit.
1 = Fault, 0 = Normal.
Converter over-current fault indication bit.
1 = Fault, 0 = Normal.
LED string short fault indication bit.
1 = Fault, 0 = Normal.
LED string open fault indication bit.
1 = Fault, 0 = Normal.
IC over-temperature fault indication bit.
1 = Fault, 0 = Normal.
2 LSB bits of LED dimming brightness set bits.
Table 5: Internal LED Dimming Brightness Register
Addr: 0x04
Bit
Bit Name
Access
Default
Description
8 MSB bits of LED dimming brightness set bits.
7:0
DIM2-9
MP3385 Rev. 1.02
8/29/2017
RW
7FH
0.098% per step. Default value is 50% dimming
brightness.
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
Table 6: OVP and OCP Protection Threshold Register
Addr: 0x05
Bit
Bit Name
Access
Default
7:3
OVP0-4
RW
11100
2:0
OCP0-2
RW
111
Description
Output over-voltage protection threshold setting based on
the OVP pin connected to the LED anode.
00000 = 18V, 00001 = 20V, 11100 = 74V, 11111 = 80V.
2V/step. Default value is 74V.
Converter over-current protection threshold.
000 = 0.15V, 111 = 0.5V. 50mV/step. Default value is
0.5V.
Table 7: Vendor ID Register
Addr: 0x06
Bit
Bit Name
Access
Default
7:0
ID0-7
R
01H
MP3385 Rev. 1.02
8/29/2017
Description
Vendor ID information.
Returns 01H when read.
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
APPLICATION INFORMATION
Selecting the Switching Frequency
The operation frequency of the converter
depends on both the resistor at OSC and the
FS0-3 bit in register 01H. If a 100kΩ resistor is
selected for Rosc (connected to OSC), the
switching frequency is set from 100kHz-900kHz
by the I2C interface. 0001b-1001b corresponds to
100kHz-900kHz respectively. Table 8 shows the
list of switching frequencies.
Table 8: Switching Frequencies
FS0-3
0000b
0001b
0010b
0011b
0100b
0101b
0110b
0111b
1000b
1001b
Switching Frequency
Converter off
100
200
300
400
500
600
700
800
900
40000
ROSC (k)
Unit
kHz
(1)
For ROSC = 100kΩ, the switching frequency is set
to 400kHz.
Setting the LED Current
The current of each LED string is set through the
current setting resistor on ISET and the full scale
LED current setting bits ILED0-7 in the 02H table.
When the INTERFACE bit in 00H is 0, the LED
current is dependent on the input PWM dimming
duty cycle. The setting formula is calculated
using Equation (2) and Equation (3):
ILED(mA)
1.98V
*KFullScale *10200
RISET (k )
(2)
When INTERFACE bit in 00H is 1,
ILED(mA)
1.98V * K DIM
*K FullScale *10200
RISET (k )
ILED(mA)
1.98V
*0.2294*10200
RISET (k )
(4)
For RISET = 46.4kΩ, the LED current is set to
100mA. Please do NOT leave ISET 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 4.7μF ceramic capacitor
in parallel with a 220µF electrolytic capacitor.
Without the I2C interface, an oscillator resistor on
OSC sets the internal oscillator frequency for the
step-up converter according to Equation (1):
FSW (kHz)
KDIM is the ratio, which is set by the dimming
current setting bits DIM0-9 in 03H and 04H.
Without the I2C interface, the current of each LED
string is set through the resistor on ISET
according to Equation (4):
(3)
Selecting the Inductor and Current Sensing
Resistor
A larger value inductor results in less ripple
current, resulting in lower peak inductor current,
which reduces stress on the N-channel MOSFET.
However, the larger value inductor has a larger
physical size, a higher series resistance, and a
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 (CCM) with high
efficiency and good EMI performance.
Calculate the required inductance value using
Equation (5) and Equation (6):
η VOUT D (1 D)2
L
(5)
2 fSW ILOAD
V
(6)
D 1 IN
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.
KFullScale is the ratio, which is set by the full scale
LED current setting bits ILED0-7 in the 02H table.
MP3385 Rev. 1.02
8/29/2017
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
Usually, the switching current is used for peakcurrent-mode control. In order to avoid hitting the
current limit, the voltage across the sensing
resistor (RSENSE) must be less than 70% of the
current-limit voltage (VSENSE), in worst cases. See
Equation (7) and Equation (8):
RSENSE
IL(PEAK)
0.7 VSENSE
IL(PEAK)
VOUT ILOAD VIN (VOUT VIN )
ηVIN
2 L FSW VOUT
(7)
(8)
The current limit setting voltage (VSENSE) is set by
the OCP0-2 bits in register 05H.
Selecting the Power MOSFET
The MP3385 is capable of driving a wide variety
of N-channel power MOSFETS. The critical
parameters of selection for 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), and
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 1.5x 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
Equation (9) and Equation (10):
IRMS(MAX) IIN(MAX) DMAX
(9)
VOUT VIN(MIN)
(10)
VOUT
The current rating of the MOSFET should be
greater than 1.5 x IRMS
DMAX
The on resistance of the MOSFET determines
the conduction loss. See Equation (11):
Pcond IRMS
2
R DS (on) k
(11)
Where k is the temperature coefficient of the
MOSFET.
MP3385 Rev. 1.02
8/29/2017
The switching loss is related to QGD and QGS,
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 turn-on and
turn-off losses. See Equation (12):
PSW
Q GS1 R G
VDS IIN f SW
VDR VTH
Q GD R G
VDS IIN f SW
VDR VPLT
(12)
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. See Equation (13):
PDR Q G VDR f SW
(13)
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
4.7μF ceramic capacitor in parallel with a 22μF
electrolytic capacitor will suffice.
Setting the Over-Voltage Protection
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 at 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, an
appropriate OVP voltage is needed. The
recommended OVP point is about 1.1 to 1.2x
higher than the output voltage for normal
operation. If the OVP pin is connected to the
anode of the LED load, the OVP protection
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MP3385 – 4-STRING WLED CONTROLLER WITH I2C INTERFACE
voltage is set by the OVP0-4 bits in register 05H.
It is not recommended to set the OVP value
higher than 80V, considering the LED return pin
voltage rating.
If the MP3385 is applied for >80V output voltage
application through an external extension,
connect a proper resistor (ROVP) between the
anode of the LED and OVP pin to change the
over-voltage point of the output (VOVP). VOVP
calculation with ROVP is given with Equation (14):
VOVP (V)=
ROVP (kΩ)+1600
*1.9
40
(14)
Where OVP0-4 bit in register 05H is the set
default.
Expanding LED Channels
The MP3385 expands the number of LED
channels by using two or three ICs in parallel. To
connect two ICs 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
driven only by the master IC. Do NOT leave
ISENSE of the slave IC floating; tie it to ground.
Apply the EN and DIM signals to both ICs. The
master IC's OVP should be higher than the slave
IC's OVP.
PCB Layout Guidelines
Efficient PCB layout is critical to reduce EMI
noise. For best results, refer to the guidelines
below:
1. Make the loop from the external MOSFET,
through the output diode and the output capacitor
as small and short as possible as they carry a
high-frequency pulse current.
2. Separate the power ground (PGND) and signal
ground (GND), then connect PGND and GND
together. All logic signals refer to the signal
ground in order to reduce the noise affection.
3. Place ceramic capacitors for VIN and VCC
pins as close as possible.
TYPICAL APPLICATION CIRCUITS
Figure 4: Driving 4 LED Strings and output voltage
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