19-0197; Rev 1; 1/95
CCFL Backlight and
LCD Contrast Controllers
_______________General Description
The MAX753/MAX754 drive cold-cathode fluorescent
lamps (CCFLs) and provide the LCD backplane bias
(contrast) power for color or monochrome LCD panels.
These ICs are designed specifically for backlit note-
book-computer applications.
Both the backplane bias and the CCFL supply can be
shut down independently. When both sections are shut
down, supply current drops to 25µA. The LCD contrast
and CCFL brightness can be adjusted by clocking sep-
arate digital inputs or using external potentiometers.
LCD contrast and backlight brightness settings are pre-
served in their respective counters while in shutdown.
On power-up, the LCD contrast counter and CCFL
brightness counter are set to one-half scale.
The ICs are powered from a regulated 5V supply. The
magnetics are connected directly to the battery, for
maximum power efficiency.
The CCFL driver uses a Royer-type resonant architec-
ture. It can provide from 100mW to 6W of power to one
or two tubes. The MAX753 provides a negative LCD
bias voltage; the MAX754 provides a positive LCD bias
voltage.
____________________________Features
♦
Drives Backplane and Backlight
♦
4V to 30V Battery Voltage Range
♦
Low 500µA Supply Current
♦
Digital or Potentiometer Control of CCFL
Brightness and LCD Bias Voltage
♦
Negative LCD Contrast (MAX753)
♦
Positive LCD Contrast (MAX754)
♦
Independent Shutdown of Backlight and
Backplane Sections
♦
25µA Shutdown Supply Current
MAX753/MAX754
______________Ordering Information
PART
MAX753CPE
MAX753CSE
MAX753C/D
MAX753EPE
MAX753ESE
MAX754CPE
MAX754CSE
MAX754C/D
MAX754EPE
MAX754ESE
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 Plastic DIP
16 Narrow SO
Dice*
16 Plastic DIP
16 Narrow SO
16 Plastic DIP
16 Narrow SO
Dice*
16 Plastic DIP
16 Narrow SO
________________________Applications
Notebook Computers
Palmtop Computers
Pen-Based Data Systems
Personal Digital Assistants
Portable Data-Collection Terminals
* Contact factory for dice specifications.
__________________Pin Configuration
TOP VIEW
V
DD
1
LADJ 2
LON 3
CON 4
CADJ 5
GND 6
REF 7
CFB 8
16 LFB
15 BATT
14 LX
MAX753
MAX754
13 LDRV
12 PGND
11 CDRV
10 CS
9
CC
DIP/SO
Block Diagram located at end of data sheet.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
CCFL Backlight and
LCD Contrast Controllers
MAX753/MAX754
ABSOLUTE MAXIMUM RATINGS
V
DD
to GND .................................................................-0.3V, +7V
PGND to GND.....................................................................±0.3V
BATT to GND.............................................................-0.3V, +36V
LX to GND............................................................................±50V
CS to GND.....................................................-0.6V, (V
DD
+ 0.3V)
Inputs/Outputs to GND (LADJ, CADJ, LON,
CON, REF, CFB, CC, CDRV, LDRV, LFB) .....-0.3V, (V
DD
+ 0.3V)
Continuous Power Dissipation (T
A
= +70°C)
Plastic DIP (derate 10.53mW/°C above +70°C) ...........842mW
Narrow SO (derate 8.70mW/°C above +70°C) .............696mW
Operating Temperature Ranges
MAX75_C_ _ ........................................................0°C to +70°C
MAX75_E_ _......................................................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
DD
= 5V, BATT = 15V, CON = LON = 5V, LX = GND = PGND = 0V, I
REF
= 0mA, all digital input levels are 0V or 5V,
T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
SUPPLY AND REFERENCE
BATT Input Range
V
DD
Supply Range
REF Output Voltage
REF Line Regulation
REF Load Regulation
V
DD
Quiescent Current
V
DD
Shutdown Current
DIGITAL INPUTS AND DRIVER OUTPUTS
Input Low Voltage
Input High Voltage
Input Leakage Current
Driver Sink/Source Current
Driver On-Resistance
CCFT CONTROLLER
Zero-Crossing-Comparator Threshold Voltage (CS)
Overcurrent-Comparator Threshold Voltage (CS)
CS Input Bias Current
VCO Frequency
DAC Resolution
V
CS
= 0V
Minimum, CFB = 5V
Maximum, CFB = 0V
Guaranteed monotonic
32
85
5
-10
1.2
20
1.3
-5
47
115
mV
V
µA
kHz
Bits
LON, CON, CADJ, LADJ; V
DD
= 4.5V
LON, CON, CADJ, LADJ; V
DD
= 5.5V
LON, CON, CADJ, LADJ; V
IN
= 0V or 5V
LDRV = CDRV = 2V
LDRV, CDRV;
V
DD
= 4.5V
Output high
Output low
0.5
10
7
2.4
±1
0.8
V
V
µA
A
Ω
No external load
4V < V
DD
< 6V
0µA < I
L
< 100µA
LON = CON = CS = LFB = CFB =
LADJ = CADJ = 5V
LON = CON = CS = LFB = CFB = LADJ
= CADJ = LX = BATT = 0V (Note 1)
5
0.5
25
4
4.5
1.21
1.25
30
5.5
1.29
0.1
15
2
40
V
V
V
%/V
mV
mA
µA
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
CCFL Backlight and
LCD Contrast Controllers
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= 5V, BATT = 15V, CON = LON = 5V, LX = GND = PGND = 0V, I
REF
= 0mA, all digital input levels are 0V or 5V,
T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
CONDITIONS
At full scale (DAC code = 31)
Feedback Voltage (CFB)
At preset DAC, CON = 0V, CADJ = 5V
(code = 15)
At zero scale (code = 0)
Feedback-Amplifier Input Bias Current
Feedback-Amplifier Unity-Gain Bandwidth
Feedback-Amplifier Slew Rate
Feedback-Amplifier Output Current
LCD CONTROLLER
Switch On-Time
Switching Period
DAC Resolution
BATT = 4V
BATT = 16V
BATT = 4V, LX = 0V
Guaranteed monotonic
At full scale (DAC code = 63)
MAX753 Feedback Voltage (REF-LFB)
At preset DAC, LON = 0V, LADJ = 5V
(code = 31)
At zero scale (code = 0)
At full scale (DAC code = 63)
MAX754 Feedback Voltage (LFB)
At preset DAC, LON = 0V, LADJ = 5V
(code = 31)
At zero scale (code = 0)
LFB Input Leakage Current
BATT Input Current
LX Input Current
TIMING
(Note 2)
Reset Pulse Width (t
R
)
Reset Setup Time (t
RS
)
Reset Hold Time (t
RH
)
CADJ, LADJ High Width (t
SH
)
CADJ, LADJ Low Width (t
SL
)
CADJ Low to CON Low or
LADJ Low to LON Low (t
SD
)
Note 1:
Maximum shutdown current occurs at BATT = LX = 0V.
Note 2:
Timing specifications are guaranteed by design and not production tested.
110
0
0
100
100
50
ns
ns
ns
ns
ns
ns
LON = CON = CS = LFB = CFB = LADJ =
CADJ = LX = 0V
LON = CON = CS = LFB = CFB = LADJ =
CADJ = 0V, LX = BATT = 15V
12
12
2
0.5
35
6
1200
893
595
1210
905
610
1240
928
625
1250
938
635
1280
963
655
1290
971
660
±150
20
20
nA
µA
µA
mV
mV
5
1.5
70
µs
µs
Bits
Source current, CFB = 0V, CC = 2.5V
Sink current, CFB = 5V, CC = 2.5V
50
200
1
0.4
MIN
1210
745
320
TYP
1250
782
343
MAX
1290
820
365
±100
nA
MHz
V/µs
µA
mV
UNITS
MAX753/MAX754
_______________________________________________________________________________________
3
CCFL Backlight and
LCD Contrast Controllers
MAX753/MAX754
______________________________________________________________Pin Description
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
NAME
V
DD
LADJ
LON
CON
CADJ
GND
REF
CFB
CC
CS
CDRV
PGND
LDRV
LX
BATT
LFB
5V Power-Supply Input
Digital Input for LCD Backplane Bias Adjustment. See Table 1.
Digital Input to Control LCD Bias Section. See Table 1.
Digital Input to Control CCFT Section. See Table 1.
Digital Input for CCFT Brightness Adjustment. See Table 1.
Analog Ground
Reference Voltage Output, 1.25V
Inverting Input for the CCFT Error Amplifier
Output of the CCFT Error Amplifier
Connect to V
DD
Leave unconnected
Power Ground Connection for LDRV
Gate-Driver Output. Drives LCD backplane N-channel MOSFET.
LCD Backplane Inductor Voltage-Sense Pin. Used to sense inductor voltage for on time determination.
Battery Connection. Used to sense battery voltage for on time determination.
Voltage Feedback for the LCD Backplane Section
FUNCTION
_______________Theory of Operation
CCFL Inverter
The MAX753/MAX754’s CCFL inverter is designed to
drive one or two cold-cathode fluorescent lamps
(CCFLs) with power levels from 100mW to 6W. These
lamps commonly provide backlighting for LCD panels
in portable computers.
Drive Requirements for CCFL Tubes
CCFL backlights require a high-voltage, adjustable AC
power source. The MAX753/MAX754 generate this AC
waveform with a self-oscillating, current-fed, parallel
resonant circuit, also known as a Royer-type oscillator.
Figure 1 shows one such circuit. The Royer oscillator is
comprised of T1, C9, the load at the secondary, Q4,
and Q5. The circuit self-oscillates at a frequency deter-
mined by the effective primary inductance and capaci-
tance. Q4 and Q5 are self-driven by the extra winding.
The current source feeding the Royer oscillator is com-
prised of L1, D5, and the MAX758A. When current from
the current source increases, so does the lamp current.
The lamp current is half-wave rectified by D7A and
4
D7B, and forms a voltage across resistor R8. The
MAX753’s error amplifier compares the average of this
voltage to the output of its internal DAC. Adjusting the
DAC output from zero scale to full scale (digital control)
causes the error amplifier to vary the tube current from
a minimum to a maximum. The DAC’s transfer function
is shown in Figure 2.
On power-up or after a reset, the counter sets the DAC
output to mid scale. Each rising edge of CADJ (with
CON high) decrements the DAC output. When decre-
mented beyond full scale, the counter rolls over and
sets the DAC to the maximum value. In this way, a sin-
gle pulse applied to CADJ decreases the DAC set-
point by one step, and 31 pulses increase the set-point
by one step.
The error amplifier’s output voltage controls the peak
current output of the MAX758A. The peak switch cur-
rent is therefore controlled by the output of the error
amplifier. The lower the error amplifier’s output, the
lower the peak current. Since the current through the
current source is related to the current through the
tube, the lower the error amplifier’s output, the lower the
tube current.
_______________________________________________________________________________________
CCFL Backlight and
LCD Contrast Controllers
MAX753/MAX754
+5V, ±5%
10
1
15
UNREGULATED INPUT VOLTAGE
1, 15, 16
2
V+
SHDN
CS
V
DD
BATT
C1
MAX754CSE
CON
CADJ
LON
LADJ
D1A
4
5
3
2
D1B
R16
3
C2
+5V CMOS
LOGIC
CONTROL
SIGNALS
R17
7
C3
D5
REF
GND
10, 11
MAX758ACWE
D2A
D2B
8
R2
R1
Q2
SS
CC
LX
12, 13, 14
11
CDRV
Q1
L1
POSITIVE
CONTRAST
VOLTAGE
L2
14
D3
7
LX
REF
D4
8
T1
12
C4
LDRV
PGND
LFB
13
Q3
12
R3
16
R4
C6
R5
5
3,4
R10
2
6
1
C10
CCFL
R6
C9
Q5
C8
Q4
D7B
GND
8
6
D6A
D6B
D7A
CFB
CC
9
C7
C5
R7
R18
R8
Figure 1. CCFL and Positive LCD Power Supply
_______________________________________________________________________________________
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