LX1692IDW MICROSEMI, LX1692IDW Datasheet - Page 11

• Manufacturer Part Number: LX1692IDW
• Description: CCFL DRVR 5.5V 20-Pin SOIC
• Manufacturer: MICROSEMI

Specifications of LX1692IDW

• Package: 20SOIC
• Driver Type: CCFL
• Maximum Operating Supply Voltage: 5.5 V

Copyright © 2004
Rev. 1.2, 12/20/2006
O
the LX1692. Upon power up or ENABLE going true, strike
mode is entered. After a successful strike, e.g., lamp is
ignited, run mode is entered. If ignition is unsuccessful, or
if the lamp extinguishes while running, a fault is declared
and the controller automatically shuts down.
O
control loops; a resonant tracking loop and a fixed
frequency loop. The fixed frequency loop is user set via the
I_R resistor and the C_R capacitor value. The resonant
tracking loop follows the natural resonant frequency of the
load.
S
current feedback voltage at the ISNS pin. If less than 1.0V
during the strike period, the lamp is considered not ignited
and Strike mode continues until ignition is detected or
strike time out (approximately 1 - 2 seconds) is reached. If
greater than 1.0V, strike is declared and a latch is set. The
IC is now in “run” mode. And threshold voltage for strike
detect is reduced to 0.3V to permit a minimum 3:1 analog
dimming ratio to be achieved.
controlled by the resonant frequency tracking loop. At
power up the lamp is not ignited and the loads’ natural
resonant frequency will be typically1.3 to 1.5 times higher
than after the lamp has ignited.
natural resonant frequency of the load. At open circuit
resonance load Q is high and produces a large rise of
voltage across the lamp, eliminating the need to use a high
transformer turns ratio.
applied to the transformer primary is minimized.
permits the use of smaller transformers that have reduced
core cross sectional area. During striking operation, ICOMP
is limited to 2.5V until ignition latch is set.
frequency as user programmed operating frequency.
TRIKING THE
PERATING
SCILLATOR
Two operating modes, Strike and Run, are employed by
The main oscillator in the LX1692 has two frequency
Lamp ignition is determined by monitoring the lamp
During strike, lamp operating frequency is always
The tracking oscillator frequency will slew to near the
Additionally, since frequency is high, the volt-seconds
When it starts the striking operation, it starts the striking
TM
M
C
ODES
L
HARACTERISTICS
AMP
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
F U N C T I O N A L D E S C R I P T I O N
Integrated Products Division
®
Microsemi
This
tracking oscillator will start to sweep the frequency up to
near to the circuit resonant frequency and it will track the
frequency to reach user programmed open lamp voltage.
immediately switches to the programmed value of the fixed
frequency oscillator. Lamp current flow is sensed by the
strike detection comparator, which decides to return PWM
timing control to the fixed frequency oscillator
F
lamp fault conditions. These include the following:
conditions, ISNS, OV_SNS, and OC_SNS.
protection is designed to prevent fire or smoke from being
generated by terminating inverter operation in the event of
failures in the high voltage components and the power
FET’s. All fault shut down events can only be reset by
ENABLE or VDDP cycling.
O
output voltage must be made higher than the normal
operating voltage of the lamp to cause ignition.
LX1692 generates this higher “strike” voltage by operating
at the open circuit resonant frequency of the load
inductance and capacitance. Because of its high unloaded
Q, a large resonant rise of voltage occurs across the lamp,
and produces ignition. Both resonant frequency and Q of
the lamp circuit are higher when the lamp is off than when
on. The lamp may not ignite immediately when specified
strike voltage is applied. It is customary to apply strike
voltage for from 0.3 to 3 seconds to insure ignition of cold,
dark, or aged lamps. The LX1692 has a programmable
time out for this purpose. During strike time out, open
lamp voltage is regulated to a value programmed by a
voltage divider across the lamp and sensed at the OV_SNS
pin.
Full Bridge Resonant CCFL Controller
AULT
PEN
And when OVSNS is detected zero cross point , then
At the moment of lamp ignition, operating frequency
The LX1692 has shut down protection for all common
When the IC is first powered on or enabled, the inverter
a. Open or broken lamp
b. High Voltage Arcing on transformer secondary side
c. Short across lamp terminals
d. Short from high side of lamp to ground
e. Short from low side of lamp to ground ( current
Three inputs from the lamp are monitored to detect these
L
sense resistor shorted)
P
AMP
ROTECTION
P
RODUCTION
D
ATA
S
HEET
LX1692
Fault
The
Page 1