Rainbow Electronics MAX754 User Manual

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 note­book-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 sep­arate digital inputs or using external potentiometers.
LCD contrast and backlight brightness settings are pre­served 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 architec­ture. 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.

________________________Applications

Notebook Computers
Palmtop Computers
Pen-Based Data Systems
Personal Digital Assistants
Portable Data-Collection Terminals

____________________________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

______________Ordering Information

PART TEMP. RANGE

MAX753CPE

MAX753CSE 0°C to +70°C
MAX753C/D 0°C to +70°C Dice*
MAX753EPE -40°C to +85°C
MAX753ESE -40°C to +85°C 16 Narrow SO
MAX754CPE
MAX754CSE 0°C to +70°C
MAX754C/D 0°C to +70°C Dice*
MAX754EPE -40°C to +85°C
MAX754ESE -40°C to +85°C 16 Narrow SO

* Contact factory for dice specifications.

0°C to +70°C

0°C to +70°C

PIN-PACKAGE

16 Plastic DIP
16 Narrow SO

16 Plastic DIP

16 Plastic DIP
16 Narrow SO

16 Plastic DIP

MAX753/MAX754

__________________Pin Configuration

TOP VIEW

V

DD

1

LADJ

2

LON

3

CON

CADJ

GND

REF

CFB

Block Diagram located at end of data sheet.

________________________________________________________________

MAX753

4

MAX754

5
6
7
8

DIP/SO

Maxim Integrated Products

Call toll free 1-800-998-8800 for free samples or literature.

LFB

16

BATT

15

LX

14

LDRV

13

PGND

12

CDRV

11

CS

10

CC

9

1

CCFL Backlight and
LCD Contrast Controllers

ABSOLUTE MAXIMUM RATINGS

VDDto 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

Inputs/Outputs to GND (LADJ, CADJ, LON,

CON, REF, CFB, CC, CDRV, LDRV, LFB).....-0.3V, (V

Continuous Power Dissipation (T

Plastic DIP (derate 10.53mW/°C above +70°C) ...........842mW

Narrow SO (derate 8.70mW/°C above +70°C) .............696mW

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.

= +70°C)

A

DD

DD

+ 0.3V)
+ 0.3V)

ELECTRICAL CHARACTERISTICS

MAX753/MAX754

(VDD= 5V, BATT = 15V, CON = LON = 5V, LX = GND = PGND = 0V, I

= T

to T

T

A

MIN

SUPPLY AND REFERENCE

DIGITAL INPUTS AND DRIVER OUTPUTS

Driver On-Resistance

CCFT CONTROLLER

VCO Frequency

, unless otherwise noted.)

MAX

No external load
4V < VDD< 6V
0µA < IL< 100µA
LON = CON = CS = LFB = CFB =

LADJ = CADJ = 5V
LON = CON = CS = LFB = CFB = LADJ

= CADJ = LX = BATT = 0V (Note 1)

LON, CON, CADJ, LADJ; VDD= 4.5V
LON, CON, CADJ, LADJ; VDD= 5.5V
LON, CON, CADJ, LADJ; VIN= 0V or 5V
LDRV = CDRV = 2V

LDRV, CDRV;
VDD= 4.5V

VCS= 0V
Minimum, CFB = 5V
Maximum, CFB = 0V
Guaranteed monotonic

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

= 0mA, all digital input levels are 0V or 5V,

REF

CONDITIONS

Output high
Output low

32 47
85 115

10

7

UNITSMIN TYP MAXPARAMETER

V430BATT Input Range
V4.5 5.5VDDSupply Range
V1.21 1.25 1.29REF Output Voltage

%/V0.1REF Line Regulation

mV515REF Load Regulation

mA0.5 2VDDQuiescent Current

µA25 40VDDShutdown Current

V0.8Input Low Voltage
V2.4Input High Voltage

µA±1Input Leakage Current

A0.5Driver Sink/Source Current

Ω

mV-10 20Zero-Crossing-Comparator Threshold Voltage (CS)

V1.2 1.3Overcurrent-Comparator Threshold Voltage (CS)

µA-5CS Input Bias Current
kHz
Bits5DAC Resolution

2 _______________________________________________________________________________________

CCFL Backlight and

LCD Contrast Controllers

ELECTRICAL CHARACTERISTICS (continued)

(VDD= 5V, BATT = 15V, CON = LON = 5V, LX = GND = PGND = 0V, I

= T

to T

T

A

MIN

Feedback Voltage (CFB)

Feedback-Amplifier Output Current

LCD CONTROLLER

Switch On-Time

MAX753 Feedback Voltage (REF-LFB)

MAX754 Feedback Voltage (LFB)

TIMING (Note 2)

CADJ Low to CON Low or
LADJ Low to LON Low (t

Note 1: Maximum shutdown current occurs at BATT = LX = 0V.
Note 2: Timing specifications are guaranteed by design and not production tested.

, unless otherwise noted.)

MAX

)

SD

CONDITIONS

At full scale (DAC code = 31)
At preset DAC, CON = 0V, CADJ = 5V

(code = 15)
At zero scale (code = 0)

Source current, CFB = 0V, CC = 2.5V
Sink current, CFB = 5V, CC = 2.5V

BATT = 4V
BATT = 16V
BATT = 4V, LX = 0V
Guaranteed monotonic
At full scale (DAC code = 63)
At preset DAC, LON = 0V, LADJ = 5V

(code = 31)
At zero scale (code = 0)
At full scale (DAC code = 63)
At preset DAC, LON = 0V, LADJ = 5V

(code = 31)
At zero scale (code = 0)

LON = CON = CS = LFB = CFB = LADJ =
CADJ = LX = 0V

LON = CON = CS = LFB = CFB = LADJ =
CADJ = 0V, LX = BATT = 15V

REF

= 0mA, all digital input levels are 0V or 5V,

UNITSMIN TYP MAXPARAMETER

1210 1250 1290

745 782 820

320 343 365

50

200

25

0.5 1.5

1200 1240 1280

893 928 963
595 625 655

1210 1250 1290

905 938 971
610 635 660

mV

nA±100Feedback-Amplifier Input Bias Current
MHz1Feedback-Amplifier Unity-Gain Bandwidth
V/µs0.4Feedback-Amplifier Slew Rate

µA

µs

µs35 70Switching Period

Bits6DAC Resolution

mV

mV

nA±150LFB Input Leakage Current

µA12 20BATT Input Current

µA12 20LX Input Current

ns110Reset Pulse Width (tR)

ns0Reset Setup Time (tRS)

ns0Reset Hold Time (tRH)

ns100CADJ, LADJ High Width (tSH)

ns100CADJ, LADJ Low Width (tSL)

ns50

MAX753/MAX754

_______________________________________________________________________________________ 3

CCFL Backlight and
LCD Contrast Controllers

______________________________________________________________Pin Description

PIN

1

MAX753/MAX754

DD

CS10

5V Power-Supply InputV
Digital Input for LCD Backplane Bias Adjustment. See Table 1.LADJ2
Digital Input to Control LCD Bias Section. See Table 1.LON3
Digital Input to Control CCFT Section. See Table 1.CON4
Digital Input for CCFT Brightness Adjustment. See Table 1.CADJ5
Analog GroundGND6
Reference Voltage Output, 1.25VREF7
Inverting Input for the CCFT Error AmplifierCFB8
Output of the CCFT Error AmplifierCC9
Connect to V
Leave unconnectedCDRV11
Power Ground Connection for LDRVPGND12
Gate-Driver Output. Drives LCD backplane N-channel MOSFET.LDRV13
LCD Backplane Inductor Voltage-Sense Pin. Used to sense inductor voltage for on time determination.LX14
Battery Connection. Used to sense battery voltage for on time determination.BATT15
Voltage Feedback for the LCD Backplane SectionLFB16

DD

_______________Theory of Operation

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 deter­mined by the effective primary inductance and capaci­tance. Q4 and Q5 are self-driven by the extra winding.
The current source feeding the Royer oscillator is com­prised 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

CCFL Inverter

FUNCTIONNAME

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 decre­mented beyond full scale, the counter rolls over and
sets the DAC to the maximum value. In this way, a sin­gle pulse applied to CADJ decreases the DAC set­point 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 cur­rent 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.

4 _______________________________________________________________________________________

CCFL Backlight and

LCD Contrast Controllers

MAX753/MAX754

+5V, ±5%

10

CS

1

V

DD

BATT

15

UNREGULATED INPUT VOLTAGE

1, 15, 16

V+

2

SHDN

D1B

CON

CADJ

LON

LADJ

LDRV

PGND

LFB

GND

D1A
4
5

3

2

D2B

D2A

L2

14

LX

13

12

16

6

9

CC

C1

MAX754CSE

11

CDRV

7

REF

C4

8

CFB

R16

3

C3C2

+5V CMOS
LOGIC
CONTROL
SIGNALS

R17

R2

R1

Q2

Q1

POSITIVE

CONTRAST

VOLTAGE

D3

Q3

R3

C6

R4

D6A

D6B

C5

D4

R5

R6

C8

Q4

C7

REF

MAX758ACWE

7

SS

8

CC

812

3,45

R10

C9

R7

GND

LX

T1

2

Q5

10, 11

D5

12, 13, 14

L1

61

CCFL

D7B

R18

C10

D7A

R8

Figure 1. CCFL and Positive LCD Power Supply

_______________________________________________________________________________________ 5