LX27901 Datasheet PDF - Microsemi Corporation
| Part Number | LX27901 | |
| Description | High Performance LED Controller | |
| Manufacturers | Microsemi Corporation | |
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LX27901
® High Performance LED Controller
TM
PRODUCTION DATASHEET
DESCRIPTION
KEY FEATURES
The LX27901 is a high performance LED Direct PWM input dimming operation can
controller optimized for LCD-TV and other be realized by inputting a dimming pulse
multi-lamp LCD display systems and train to DIM pin directly.
provides a cost competitive solution for off- The ACU_BRITE algorithm allows the DC
PFC LED drive applications.
to DC converter to be turned off when the
The controller provides a pair of PWM digital dimming operation is at off state to
drive signals with adequate capacity to drive eliminate no-load power losses. The
a half bridge or other double ended DC to controller also provides a proprietary
DC converter circuit with the addition of synchronous regulation function to allow the
simple external circuitry to provide safety user to control the LED current and dimming
isolation.
operation from an un-regulated switching
The device includes a regulated 5.25V power supply source to minimize the number
output (VDD) activated by the ENABLE of power conversion stages and the
input working from the VIN input voltage of associated losses and component costs. In
up to 27V. VDD is capable of providing synchronous regulation mode, AOUT and
5mA source current to external circuitry BOUT form a pair of drive signals to control
while supplying the on chip driver stage and the LED string pairs in AC current mode,
the control circuitry.
and COUT provides another option to
The controller allows the user to utilize control the LED in DC current mode.
two different converter drive schemes, LLC A versatile set of system monitoring and
resonant or PWM control mode, selected by protection functions are incorporated in the
the signal level at ENABLE pin, to best fit a LX27901 design to provide reliable
wide spectrum of application needs.
protection of the device and the system.
In addition, a proprietary ACU_BRITE
algorithm is incorporated in the dimming
control operation to allow the user to
adaptively adjust the PWM dimming duty to
achieve accurate brightness control over a
wide dimming duty cycle range while
maintaining the highest operating efficiency.
Three input pins, ISNS, VSNS and
UVS/SYN are assigned to support the
regulation and protection sense feedback
needs over wide range of application
configurations. Likewise a dedicated fault
indication pin allows the user to generate a
direct fault report to the system and
configure addition protection features with
The LX27901 supports analog LED current simple external circuits.
control utilizing the BRTA pin as the analog
LED current setting function.
The device is available in 16 lead SOIC
surface mount package in the industrial
temperature range.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
Three Selectable Drive Modes to
Support Wide Range of Topologies
Optimized Solution for Off PFC LED
Drive Applications
0.8A Source & Sink Drive Capacity
On Chip 5.25V Regulator
Direct Connection to Input Voltage
up to 27V
ACU_BRITE Algorithm to Provide
Accurate Brightness Control at
Highest Operating Efficiency Over
Wide Dimming Duty Range
User Selectable Dimming Mode
Control
Synchronous Regulation Function
to Minimize Power Conversion
Stage
Accurate LED Current Matching In
Combination With Microsemi’s Non-
dissipative Balancing Technology
Robust Operation at Open and
Short LED Conditions
Compensated External and Internal
PWM Dimming Operation
Dedicated Fault Indication
LED Current and Voltage
Monitoring
RoHS Compliant & Halogen Free
APPLICATIONS
LCD LED Backlight TV
LCD LED Backlight Monitors
Other LED Backlight Systems
PACKAGE ORDER INFO
TA (C)
D
Plastic SOIC 16 Pin
RoHS Compliant / Pb-free
-40 to +85
LX27901ID
Note: Available in Tape & Reel. Append the letters “TR” to the part number.
(i.e. LX27901ID-TR)
THERMAL DATA
JA = 82.2 C/W
THERMAL RESISTANCE-JUNCTION TO AMBIENT
Junction Temperature Calculation: TJ = TA + (PD 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.
Copyright 2011
Rev. 1.1
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
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TM
Name
UVS/SYN
VSNS
ISNS
COMP
C_OUT
AOUT
BOUT
GND
Copyright 2011
Rev. 1.1
Pin #
8
9
10
11
12
15
13
14
LX27901
® High Performance LED Controller
PRODUCTION DATASHEET
FUNCTIONAL PIN DESCRIPTION
Description
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
110mV, the threshold of over current is 630mV, and the threshold for short circuit is 1000mV. A
fault flag will be declared if ISNS signal stays below 110mV or above 630mV over defined counts,
and the operation will be cut off immediately when ISNS signal goes above 1000mV.
Output of the error amplifier. The error amplifier is a Gm type that provides robust control behavior
and simple compensation. The signal on this pin feeds to the PWM modulation circuit to control
the drive output to regulate the LED current. At start up the voltage of this pin is controlled by the
soft start circuit.
Gate signal to drive an additional MOSFET for LED current regulation. The signal is in
synchronous with the C_R oscillator frequency and is leading edge modulated by the output of the
error amplifier in LLC and synchronous regulation modes and trailing edge modulated in PWM
half bridge drive mode. This signal can be used in combination with AOUT and BOUT to extend
the regulation range in LLC operation mode or provide additional driving capabilities in
synchronous regulation mode.
Gate drive output. These driver outputs are capable of providing 0.8A source and sink current at
nominal operating voltage. Dead time is inserted to prevent possible shoot through at full duty
cycle when these signals are used for half bridge or full bridge driving. Internal pull down resistors
of 20kΩ is provided at each pin. When the controller is in resonant drive mode AOUT and BOUT
are driven to maximum duty and their switching frequency varies with COMP signal level; when
the controller is in PWM drive mode these two outputs generate pulse width modulated drive
signals at fixed frequency; and when the controller is in synchronous LED drive mode, UVS/SYN
receives the synchronization signal, AOUT outputs a NFET drive signal in synchronous with the
positive cycle of the UVS/SYN input and BOUT outputs a PFET drive signal in synchronous with
the negative cycle of the UVS/SYN input to drive respective external power devices to control the
LED current directly. Different from the PWM drive mode, the pulse width of AOUT and BOUT is
leading edge modulated in synchronous drive mode.
Ground return of the on chip circuit. It is important to provide a low impedance ground plane to
this pin and the signal control circuitry in PCB layout, and not let the ground return current of the
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
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| Information | Total 19 Pages | |
| Link URL | [ Copy URL to Clipboard ] | |
| Download | [ LX27901.PDF Datasheet ] | |
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