LX27901
TM
®
Multipurpose High Performance LED Controller
P
RELIMINARY
D
ATASHEET
DESCRIPTION
KEY FEATURES
LLC, PWM and proprietary
synchronous modes to drive the LED
strings
LED strings can be dimmed by PWM
or analog methods
Proprietary algorithm to provide
accurate brightness control at high
efficiency over wide dimming duty
cycle range
Accurate parallel LED strings current
matching using Microsemi’s patented
non-dissipative current-balancing
technology
Robust protection from open or
shorted LED conditions
Dedicated fault indication
0.8A Source & Sink Drive Capability
On Chip 5.25V Regulator
Direct connection to input voltage
rail up to 27V
LLC max operating frequency to 1
MHz, PWM to 150 kHz
Synchronous regulation function to
minimize power conversion stage
RoHS compliant & halogen Free
APPLICATIONS
LCD LED Backlight TV
LCD LED Backlight Monitors
Other LED Backlight Systems
The LX27901 is an extremely
versatile high-performance
controller for driving LEDs from the
HVDC (output) rail of a standard
PFC front-end.
The controller allows the user to
utilize three different converter
drive schemes, LLC (resonant),
conventional PWM control, and
Microsemi’s proprietary
synchronous scheme, all selectable
by the multi-function ENABLE pin.
In non-resonant mode, the
controller provides two 180° phase-
shifted pulse-width modulated drive
signals for implementing various
two-switch DC-DC converter
topologies, such a half-bridge and
asymmetrical forward converter. It
can also be used for one-switch
topologies.
The LX27901 is designed to operate
with Microsemi’s proprietary
lossless (magnetic) current
balancing schemes.
The controller also provides a
proprietary synchronous regulation
function to allow the user to control
the LED current and dimming from
an unregulated switching power
supply source, to minimize the
number of power conversion stages
and the associated losses and
component costs.
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Microsemi
.CO
M
A versatile set of system monitoring
and protection functions are
incorporated in the LX27901 design
to provide reliable protection of the
device and the system. These can
account for shorted and open LED
strings for example.
Three input pins, ISNS, VSNS and
UVS/SYN are assigned to support
regulation and protection. A
Direct PWM input dimming
dedicated fault indication pin allows
operation can be realized by
the user to generate a direct fault
inputting a suitable dimming pulse
report to the system and configure
train to the DIM pin. The LX27901
supports analog LED current control addition protection features with
utilizing the BRTA pin for setting the simple external circuits.
analog LED current.
The device is available in 16 lead
SOIC surface mount package in the
industrial temperature range.
In addition, a proprietary dimming
algorithm ACU_BRITE
®
is
incorporated. The controller
Refer to the Application Note titled
integrates the pulsed LED current
“Some
Proprietary LED Current
and compares it with a reference for
Balancing Techniques”.
very accurate brightness control
irrespective of duty cycle.
LX27901
LX27901
Page 1
Copyright
2012
Rev. 0.3_03-27-2013
Microsemi
Analog Mixed Signal Group
One Enterprise Aliso Viejo, CA 92656 USA
LX27901
TM
®
Multipurpose High Performance LED Controller
P
RELIMINARY
D
ATASHEET
IMPORTANT:
For the most current data, consult
MICROSEMI’s
website:
http://www.microsemi.com
W W W.
Microsemi
.CO
M
PACKAGE ORDER INFO
THERMAL DATA
T
A
(C)
-40 to +85
D
Plastic SOIC 16 Pin
RoHS Compliant / Pb-free
JA
= 82.2
C/W
THERMAL RESISTANCE
-
JUNCTION TO AMBIENT
LX27901ID
Note: Available in Tape & Reel. Append the letters “TR” to the part number.
(i.e. LX27901ID-TR)
Junction Temperature Calculation: T
J
= T
A
+ (P
D
x
JA
).
The
JA
numbers are guidelines for the thermal
performance of the device/pc-board system. All of the
above assume no ambient airflow.
JA
number above is
with 4-layer pcb board.
AABSOLUTE
MAXIMUM RATINGS
Supply Input Voltage, VIN ............................................................................... 0.3V to 36V
Signal Outputs, VDD, AOUT, BOUT, C_OUT..............................................-0.3V to 6.5V
Signal Inputs, C_R, BRTA .................................................................. -0.3V to VDD+0.3V
Signal Inputs, ENABLE, DIM, ISNS, VSNS, UVS/SYN ................... -0.3V to VDD+0.3V
Signal Outputs COMP, SST/BCOM, FAULT ............................................... -0.3V to VDD
Maximum Junction Temperature ............................................................................... 150°C
Storage Temperature Range ......................................................................... -65C to 150C
Peak Package Solder Reflow Temperature (40 seconds maximum exposure) ........... 260°C
Lead Temperature. (Soldering 10 seconds)................................................................ 300°C
Notes: Exceeding these ratings could cause damage to the device. All voltages are with respect to
GND. Currents are positive into, negative out of specified terminal. These are stress ratings
only and functional operation of the device at these or any other conditions beyond those
indicated under “Recommended Operating Conditions” are not implied. Exposure to
“Absolute Maximum Ratings” for extended periods may affect device reliability.
PACKAGE PIN OUT
VIN
ENABLE
C_R
BRTA
DIM
SST/
BCOM
FAULT
UVS/
SYN
VDD
AOUT
GND
BOUT
C_OUT
COMP
ISNS
VSNS
LX27901ID
D P
ACKAGE
(Top View)
RoHS / Pb-free Matte Tin Pin Finish
ELECTRICAL CHARACTERISTICS
Unless otherwise listed, the following specifications apply over the operating ambient temperature of -40
°
C < Temp < 85
°
C, and VIN = 7.5V to 27V, except where
otherwise noted and the following test conditions: VIN = 12V, C
C_R
= 330pF, R
C_R
= 15K
MSC
LX27901ID
xxxx
Parameters
Symbol
Test Conditions/Comments
MIN
TYP
MAX
Units
Power
Controller Input Voltage
Controller Operating Voltage
Power Supply Input Current
Sleep Mode Current
VDD Off Voltage
VIN
VDD
IIN
IDD
SLEEP
1µF bypass cap on VDD pin,
I
VDD
= 0 to 5mA
AOUT, BOUT = no load, VDD = no load
VIN = 24V, V
ENABLE
< 0.8V
ENABLE < 0.8V
7.5
5.0
5.25
7
200
0.1
27
5.5
10
400
V
V
mA
µA
V
LX27901
LX27901
Enable
ENABLE On
EN
H
1.7
V
Page 2
Copyright
2012
Rev. 0.3_03-27-2013
Microsemi
Analog Mixed Signal Group
One Enterprise Aliso Viejo, CA 92656 USA
LX27901
TM
®
Multipurpose High Performance LED Controller
P
RELIMINARY
D
ATASHEET
ELECTRICAL CHARACTERISTICS
Unless otherwise listed, the following specifications apply over the operating ambient temperature of -40
°
C < Temp < 85
°
C, and VIN = 7.5V to 27V, except where
otherwise noted and the following test conditions: VIN = 12V, C
C_R
= 330pF, R
C_R
= 15K
W W W.
Microsemi
.CO
M
Parameters
Shut Down
LLC Resonant Mode
Threshold
PWM Switching Mode
Threshold
Synchronous LED Drive Mode
Threshold
Input High Current
Input Low Current
Symbol
EN
L
V
LLCTH
V
PWMTH
V
SYN
EN
IIH
EN
IIL
Test Conditions/Comments
MIN
TYP
MAX
0.8
Units
V
V
V
V
µA
µA
LLC resonant drive mode, VDD = 5.25V
PWM switching drive mode, VDD = 5.25V
Synchronous LED drive mode, VDD = 5.25V
ENABLE = 2V
0V < V
ENABLE
< 0.8V
2
3
4
3
4
VDD
10
5
Under Voltage Lockout
VDD Startup Threshold
VDD UVLO Threshold
VDD UVLO Hysteresis
VDD
UVLOR
VDD
UVLOF
VDD
UVLOH
Rising Threshold.
Falling Threshold.
4.35
4.0
4.6
4.2
0.4
4.8
4.45
V
V
V
Output
Output Resistance
Output Resistance
Dead Time
C_OUT Output Resistance
R
SINK
R
SOURCE
OUT
DT
R
C_OUT
I
SINK
, AOUT and BOUT, T
A
= 25°C
I
SOURCE
, AOUT and BOUT, T
A
= 25°C
T
A
= 25°C, at full duty
Source and sink
250
5
5
330
15
6
6
410
20
Ω
Ω
ns
Ω
Switching Frequency Oscillator
Switching Frequency
Tolerance
Max Oscillator Frequency
LLC Frequency Control
Current Source
Ramp Valley Voltage
Ramp Peak Voltage
Synchronization Range
OSCVV
OSCPV
Ratio of UVS/SYN input over C_R oscillator
free run frequency
T
A
= 25°C, input, Corresponds to 2V after
4.75X internal amplifier.
Linear operation range for internal circuit
4.75 times of ISNS signal. Input outside the
range is clamped at upper or lower limit
internally.
K
PRAMP
Source and Sink
1.05
OSCIN
PWM
OSC
MAX_LLC
T
A
= 25°C, Frequency of AOUT, BOUT in PWM
mode, C
C_R
=330pF, R
C_R
= 15K.
T
A
= 25°C, Frequency of AOUT, BOUT in LLC
mode, C
C_R
=330pF, R
C_R
= 15K.
V
ENABLE
< 2.8V
128.8
140
1
0
0.5
2.5
3
200
151.2
kHz
MHz
µA
V
V
Ratio
LED Dimming Control
LX27901
LX27901
ISNS Reference
ISNS Linear Input Range
BRTA Input Range
Pre-Amplifier Gain
Error Amp Output Capacity
ISNS
REF
414.6
800
0.5
421
426.4
mV
mV
2.0
4.75
100
V
µA
Page 3
Copyright
2012
Rev. 0.3_03-27-2013
Microsemi
Analog Mixed Signal Group
One Enterprise Aliso Viejo, CA 92656 USA
LX27901
TM
®
Multipurpose High Performance LED Controller
P
RELIMINARY
D
ATASHEET
ELECTRICAL CHARACTERISTICS
Unless otherwise listed, the following specifications apply over the operating ambient temperature of -40
°
C < Temp < 85
°
C, and VIN = 7.5V to 27V, except where
otherwise noted and the following test conditions: VIN = 12V, C
C_R
= 330pF, R
C_R
= 15K
W W W.
Microsemi
.CO
M
Parameters
DIM Input Voltage Range
PWM Dimming Mode Control
Threshold
Symbol
V
DIM
V
PDMODETH
Test Conditions/Comments
Effective for duty from 0 to 100%
Voltage level of FAULT pin, in ACU_BRITE
PWM dimming mode when below threshold; in
conventional PWM dimming mode when
above threshold.
MIN
0.5
2.8
TYP
MAX
2.0
Units
V
V
3.0
3.2
Fault Monitoring and Protection
VSNS Threshold
VSNS Clamping Current
Source
UVS/SYN Threshold
UVS/SYN Input Range
ISNS Fault Threshold
Over Current Threshold
Short Circuit Threshold
Fault Count
Fault reset Interval
Fault Output Sinking Capacity
Fault Output Open Impedance
VSNS
TH
I
CLAMP
UVS/SYN
TH
V
UVS/SYN
V
ISNSTH
OC
TH
SC
TH
FC
F
RESET
F
SINK
R
F
Fault when above the threshold
Pull down source at COMP pin
Fault when below the threshold, positive and
negative input
Functional operation range, positive and
negative input
Fault when below the threshold
Upper threshold for ISNS input
Upper threshold for ISNS input
At clock frequency of AOUT, BOUT
Interval for resetting fault counter, At clock
frequency of AOUT, BOUT
VFAULT ≤ 0.8V, TA = 25°C
When in open state
4
5
0.35
-0.5
85
550
870
100
600
930
256
32768
6
1.8
2.0
160
0.4
0.45
4
115
650
990
2.2
V
µA
V
V
mV
mV
mV
Count
Count
mA
MΩ
Bias & References
Internal Master Reference
Voltage
Soft Start Charging Source
VREF
I
SSC
C_B Charging source at start up
1.2
2
V
µA
Power-Up Sequencing
Power On Reset Time
Start up Time Out
TPOR
TSTART
After UVLO of VDD released
After POR
50
32768
µs
Count
LX27901
LX27901
Name
Pin #
FUNCTIONAL PIN DESCRIPTION
Description
Input voltage pin. A built-in regulator is connected to this pin to step down the input voltage to the internal
operating voltage VDD. This pin can accept input voltage from 10V to 27V to provide the flexibility of
interfacing with either 12V or 24V system supply. A low ESR decoupling capacitor of not less than 1µF
should be connected from this pin to GND with low impedance traces.
Enable pin to control the on/off operation of the controller. A logic low signal <0.8V on this pin sets the
Page 4
VIN
1
ENABLE
Copyright
2012
Rev. 0.3_03-27-2013
2
Microsemi
Analog Mixed Signal Group
One Enterprise Aliso Viejo, CA 92656 USA
LX27901
TM
®
Multipurpose High Performance LED Controller
P
RELIMINARY
D
ATASHEET
Name
Pin #
FUNCTIONAL PIN DESCRIPTION
Description
controller in sleep mode to save energy, and a signal > 2V activates the controller operation. The DC signal
level on this pin also sets the drive mode of the controller. When 2V<V
ENABLE
<3V the AOUT, BOUT signals
are set in LLC resonant drive mode. When 3V<V
ENABLE
<4V the controller drives the power converter in
normal PWM drive mode; and when V
ENABLE
>4V the controller is set in synchronous LED drive mode.
Converter operating frequency programming terminal. A pull-up resistor from this pin to VDD and a
capacitor connected from this pin to ground determines the switching frequency of the inverter.
Terminal for programming the analog LED current setting. An analog signal is accepted from this pin to set
the reference level for the LED current control loop.
PWM dimming control input. V
DIM
> 2V sets the dimming operation in continuous analog mode. A PWM
signal of low level <0.5V and high level > 2V will force the PWM dimming operation to follow the PWM
signal directly. Input level <0.5V will stop the controller output.
For PWM dimming brightness compensation and soft start. The elapsed dimming demand and the
accumulated LED current over the active dimming period are compared at this pin. The comparison result
is used to control the LED light output to exactly match the dimming demand with compensation for the
distortion of the LED current during dimming operation. At start up this pin is connected to a 2µA charging
current source to control the soft start process. An internal active pull down circuit is connected from this
pin to COMP to force the COMP voltage rise slowly with the charge of the capacitor at this pin. Soft start
completes when the voltage rises to 2.5V and the control enters normal operation mode. The 2µA charging
source and the COMP pull down circuit is disconnected then, and this pin is connected to the brightness
compensation circuit.
Fault indication pin with open drain output. Internally pulled down when an open LED string, severely
shorted LED string, over voltage of the LED strings, or over current occurs. Once latched, the fault signal
can only be reset by ENABLE or power recycling. The voltage level at this pin during normal operation also
sets the operation mode of dimming control. When the voltage is above 3V the COMP signal is turned on
and off by the digital dimming control signal and AOUT, BOUT and C_OUT are turned on and off
accordingly by the COMP signal. When the voltage at the FAULT pin is below 3V the COMP signal is
turned on and off by the control signal from the ACU_BRITE dimming control algorithm, and AOUT, BOUT
and C_OUT are turned on and off accordingly by the COMP signal. The voltage level of this pin during
normal operation can be set by an external resistive divider.
Sense for under voltage conditions. A threshold of 0.4V is set internally to compare the sense feedback
signal to this pin when the LED strings are on. A fault will be declared if the sensed signal stays below the
threshold over certain counts set by the internal circuitry. LED string current and voltage sense signals can
be fed to this pin to detect open or short string conditions. When the controller is set in synchronous
regulation mode UVS/SYN will receive the synchronization signal from the power supply to synchronize the
switching frequency of AOUT and BOUT. An internal rectifier circuit is included to allow an AC input signal
to be connected to this pin directly.
Voltage sense input pin. The voltage signal on this pin feeds the over voltage detection circuit. A threshold
of 2V is set internally for fault detection. When the voltage sense signal reaches the threshold of 2V, a
clamping current source will be activated to pull down COMP signal to limit the sensed voltage. In the
meanwhile, the fault monitoring circuit will start counting the accumulated fault duration and set up the fault
flag when the fault count reaches pre-determined counts.
Current sense input pin. A full wave rectifier circuit is built in to allow AC input to this pin. The regulation
point at this pin is 421mV which is amplified by 4.75 times and then fed to the error amplifier to compare
with a reference signal of 2V to regulate the LED current. This signal is also used to detect open LED, over
current and short circuit conditions. The threshold for open LED is 100mV, the threshold of over current is
600mV, and the threshold for short circuit is 930mV. A fault flag will be declared if ISNS signal stays below
100mV or above 600mV over defined counts, and the operation will be cut off immediately when ISNS
signal goes above 930mV.
Page 5
W W W.
Microsemi
.CO
M
C_R
3
BRTA
4
DIM
5
SST/BCOM
6
FAULT
7
UVS/SYN
8
VSNS
9
LX27901
LX27901
ISNS
10
Copyright
2012
Rev. 0.3_03-27-2013
Microsemi
Analog Mixed Signal Group
One Enterprise Aliso Viejo, CA 92656 USA
