lx1688 Microsemi Corporation, lx1688 Datasheet - Page 10

• Manufacturer Part Number: lx1688
• Description: Multiple Lamp Ccfl Controller
• Manufacturer: Microsemi Corporation

Copyright © 2001
Rev. 1.2, 2006-03-09
A
controller by showing a practical example. Three identical
inverter modules are connected to each other and each
module drives a single lamp. One module configured as a
master and two others configured as slaves.
Figure 1, the schematic provides all necessary functions
such as high voltage feedback for regulation the peak lamp
voltage, short-circuit protection, open lamp sensing and
lamp current regulation needed for a typical application.
The section follows with measurement waveforms and list
of material of the actual modules. For more detail design
procedure and circuit description please refer to application
note (AN-13), which is available in Microsemi’s web site.
I
±10%, in this application all modules were driven by the
same power voltage (a constant 5.0V), which provides
VDD for controllers, and input voltage for the power
section. Notice that VDD feeds all analog signals and
VDD_P feeds only the output driver stage, these two
signals should be filtered separately (Figure 1).
S
current sources that set timing parameters. Equation (2)
gives the relationship between Lamp frequency (FLAMP)
and (RI_R), R1 in schematic. For this application we
choose R6=80.6 KΩ, which results to a lamp frequency at
62.0 KHz.
D
or DC’ dim input that allows either a PWM or DC input
without requiring external conditioning.
applying a PWM signal to BRITE pin.
notice that it is possible to dim each module quite
separately.
this application it is connected to VDD which means active
high enable with active high full brightness.
48-320 HZ. No capacitor between CPWM1 and CPWM2 is
necessary.
NPUT
ETTING LAMP FREQUENCY
PPLICATION EXAMPLE WITH
IMMING
This section will highlight the features of LX1688
A complete schematic hooked up a a master is given in
The LX1688 controller can operate at 3.3 to 5.0V
The value of R1 determines magnitude of internal
The LX1688 includes highly integrated universal ‘PWM
In this application we choose Digital Dimming by
All modules were driven by the same PWM signals, but
BEPOL pin has three different modes (see table 1), in
The PWM signal can be varied in frequency between
TM
V
OLTAGE
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LX1688
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S
and to the VDD for a slave will do master and slave
configuration. As shown in figure 2, module (A)
configured as master and modules (B) and (C) configured
as slaves.
S
modules, it is required to connect the RMP_RST pin of all
the modules together and connect PHA_SYNC pin of all
the modules together.
L
the overall noise and EMI for the module.
independent loop that doesn’t interface with the more
sensitive analog control function, therefore LX1688
provides two power inputs with separate ground pins
(analog/signal), VDD feeds all analog signals and VDD_P
feeds only the output drivers, as shown in figure1 these
two pins (pin 23, 24) are separated and filtered by R14, C2
and C7. The connection of two ground pins should be at
only one point as shown in figure1.
and all periphery components such capacitors should be
located as closed as possible to the controller.
O
taken from the actual circuits and will show the operation
of the modules in different modes when three identical
modules are synchronized, one as a master, and two others
as slaves.
ETTING
YNCHRONIZATION OF
AYOUT CONSIDERATION
SCILLOSCOPE
Simply connecting pin 14 to the ground for a master
To synchronize the Lamp frequency and phase of all
By designing the layout in a proper way we can reduce
The gate drivers for MOSFETs should have an
The power traces should be short and wide as possible
The following oscilloscope waveform pictures are
Multiple Lamp CCFL Controller
M
P
ASTER
RODUCTION
W
/S
AVEFORMS
LAVE CONFIGURATION
F
REQUENCY AND
D
ATA
P
ICTURES
S
HEET
P
HASE
LX1688
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