p
mercial Tem
xtended Com ˚C to 70˚C
E
-20
ment
ndheld Equip
Portable Ha
for
FEATURING
ature Range
er
JULY 2000
ML4876*
LCD Backlight Lamp Driver with Contrast
GENERAL DESCRIPTION
The ML4876 is an ideal solution for driving small cold
cathode fluorescent tubes (CCFL) used in liquid crystal
display (LCD) backlight applications. It provides the
dimming ballast control and the contrast control for the
LCD display.
By utilizing differential drive the ML4876 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 ML4876 is optimized for portable 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
FEATURES
s
s
s
s
s
s
s
s
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
Low switching losses
Resonant threshold detection
Buck regulator uses synchronous rectification
BLOCK DIAGRAM
13
VDD
HVDD
15
6
ON/OFF
VREF
5
MASTER
BIAS
&
UVLO
LINEAR
REGULATOR
ONE
SHOT
VDD
DR3
DR1
DR1
DR2
NEG
EDGE
DELAY
S Q
R Q
LON
4
+
Q S
–
Q R
16V
–
+
F GATE
12
F ILIM
20
0.1V
FEA–
2
FEA+
3
+
–
–
–
+
+
FEA OUT
1
9
C
T
8
LEA OUT
CLK
OSCILLATOR
Q S
Q R
RESONANT
THRESHOLD
DETECTOR
0.5V
17
GND
18
B ON
19
B OFF
11
B SYNC OUT
L RTD
10
L GATE 1
14
Q
T
Q
DR2
L GATE 2
16
–
–
+
+
0.2V
LEA–
7
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
