ML4877 Datasheet, PDF (1/11 Pages) Micro Linear Corporation – LCD Desktop Backlight Lamp Driver

NEW!
30W ^{CCFL Inverter Design}
JULY 2000
ML4877*
LCD Desktop Backlight Lamp Driver
GENERAL DESCRIPTION
FEATURES
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.
s Ideal for 30W inverter designs, 1 to 8 lamp design
s PWM dimming capability
s Backlight lamp driver with differential drive
s Up to 30% lower power for same light output
s Low standby current (<10µA)
s Improved efficiency (»95%)
s Allows all N-channel MOSFET drive
s Adjustable lamp out detect with latch
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.
s Resonant threshold detection and synchronous
rectification
s Positive input for dimming control
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.
* THIS PART IS END OF LIFE AS OF JULY 1, 2000
BLOCK DIAGRAM
AZR VDD
2 13
VDD
HVDD 12
LINEAR
REGULATOR
VREF 5
MASTER
BIAS
&
UVLO
ON/OFF 15
SS
QS
QR
B ON
19
B OFF
20
B SYNC OUT
11
10 L RTD
DR3
DR1
ONE
SHOT
SQ
RQ
DR1
NEG
EDGE
DELAY
+
– VDD
CLK
RESONANT
THRESHOLD
DETECTOR
OSCILLATOR
DR2
Q
T
Q
DR2
14 L GATE 1
16 L GATE 2
–
+
SS
+
6 L ILIM
–
0.5V
8 LEA OUT
–
7 LEA–
+
1 LEA+
17
PGND
18
GND
4
9
RT
CT
3
SS CAP
1