NEW!
Inverter D
0W CCFL
3
esign
JULY 2000
ML4877*
LCD Desktop Backlight Lamp Driver
GENERAL DESCRIPTION
The ML4877 is an ideal solution for driving multiple cold
cathode fluorescent tubes (CCFL) used in liquid crystal
display (LCD) backlight applications. It provides dimming
ballast control for the LCD display.
By utilizing differential drive the ML4877 can deliver the
same light output with significantly less input power
compared to existing single ended drive schemes.
Improvements as high as 30% can be realized when using
low power lamps and advanced LCD screen housings. This
increased light output is achieved because the differential
drive configuration is much less sensitive, and therefore
less power is wasted in the capacitive parasitics that exist
in the backlight housing. An additional benefit of this
configuration is an even distribution of light.
The IC includes an adjustable lamp out detect circuit that
latches the IC off when a lamp fault is detected. Also, the
unique architecture of the ML4877 allows the
development of a backlight system that will inherently
meet the UL requirements for safety.
The ML4877 is optimized for large LCD applications
applications where high efficiency is critical to maximize
battery life. The high efficiency is achieved by a resonant
scheme with zero voltage switching.
FEATURES
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Ideal for 30W inverter designs, 1 to 8 lamp design
PWM dimming capability
Backlight lamp driver with differential drive
Up to 30% lower power for same light output
Low standby current (<10µA)
Improved efficiency (»95%)
Allows all N-channel MOSFET drive
Adjustable lamp out detect with latch
Resonant threshold detection and synchronous
rectification
Positive input for dimming control
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* THIS PART IS END OF LIFE AS OF JULY 1, 2000
BLOCK DIAGRAM
AZR
2
VDD
13
VDD
HVDD 12
LINEAR
REGULATOR
B ON
19
B OFF
20
B SYNC OUT
11
10 L RTD
DR3
DR1
DR1
DR2
Q
14 L GATE 1
VREF 5
MASTER
BIAS
&
UVLO
ONE
SHOT
S Q
R Q
NEG
EDGE
DELAY
T
Q
DR2
16 L GATE 2
+
–
0.5V
6
L ILIM
ON/OFF 15
SS
Q S
Q R
+
–
VDD
CLK
OSCILLATOR
SS
17
PGND
18
GND
4
R
T
9
C
T
3
SS CAP
RESONANT
THRESHOLD
DETECTOR
–
–
+
+
8
7
1
LEA OUT
LEA–
LEA+
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
