MAXIM MAX753, MAX754 User Manual

_______________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

* Contact factory for dice specifications.

MAX753/MAX754

CCFL Backlight and

LCD Contrast Controllers

________________________________________________________________ Maxim Integrated Products 1

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

LFB

BATT

LX

LDRV

CON

LON

LADJ

V

DD

MAX753
MAX754

PGND

CDRV

CS

CC

CFB

REF

GND

CADJ

DIP/SO

TOP VIEW

__________________Pin Configuration

19-0197; Rev 1; 1/95

PART TEMP. RANGE

MAX753CPE

0°C to +70°C

MAX753CSE 0°C to +70°C

MAX753C/D 0°C to +70°C Dice*

16 Narrow SO

16 Plastic DIP

PIN-PACKAGE

MAX753EPE -40°C to +85°C

MAX753ESE -40°C to +85°C 16 Narrow SO

16 Plastic DIP

MAX754CPE

0°C to +70°C

MAX754CSE 0°C to +70°C

MAX754C/D 0°C to +70°C Dice*

16 Narrow SO

16 Plastic DIP

MAX754EPE -40°C to +85°C

MAX754ESE -40°C to +85°C 16 Narrow SO

16 Plastic DIP

Block Diagram located at end of data sheet.

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.

MAX753/MAX754

CCFL Backlight and
LCD Contrast Controllers

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= 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.)

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.

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

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

Guaranteed monotonic

Maximum, CFB = 0V

Minimum, CFB = 5V

VCS= 0V

LON, CON, CADJ, LADJ; VDD= 5.5V

LON, CON, CADJ, LADJ; VDD= 4.5V

LDRV, CDRV;
VDD= 4.5V

No external load

4V < VDD< 6V

0µA < IL< 100µA

LDRV = CDRV = 2V

LON, CON, CADJ, LADJ; VIN= 0V or 5V

CONDITIONS

Bits5DAC Resolution

85 115

kHz

32 47

VCO Frequency

µA-5CS Input Bias Current

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

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

7

Ω

10

Driver On-Resistance

A0.5Driver Sink/Source Current

µA±1Input Leakage Current

V4.5 5.5VDDSupply Range

V430BATT Input Range

V2.4Input High Voltage

V0.8Input Low Voltage

µA25 40VDDShutdown Current

V1.21 1.25 1.29REF Output Voltage

%/V0.1REF Line Regulation

mV515REF Load Regulation

mA0.5 2VDDQuiescent Current

UNITSMIN TYP MAXPARAMETER

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

Output high

Output low

LON = CON = CS = LFB = CFB = LADJ
= CADJ = LX = BATT = 0V (Note 1)

SUPPLY AND REFERENCE

DIGITAL INPUTS AND DRIVER OUTPUTS

CCFT CONTROLLER

MAX753/MAX754

CCFL Backlight and

LCD Contrast Controllers

_______________________________________________________________________________________ 3

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

ELECTRICAL CHARACTERISTICS (continued)

(VDD= 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.)

At zero scale (code = 0)

At full scale (DAC code = 31)

At full scale (DAC code = 63)

Guaranteed monotonic

BATT = 4V, LX = 0V

BATT = 16V

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

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

At zero scale (code = 0)

BATT = 4V

CONDITIONS

µA12 20LX Input Current

µA12 20BATT Input Current

nA±150LFB Input Leakage Current

595 625 655

893 928 963

mV

1200 1240 1280

MAX753 Feedback Voltage (REF-LFB)

Bits6DAC Resolution

µs35 70Switching Period

0.5 1.5

µs

25

Switch On-Time

745 782 820

mV

1210 1250 1290

Feedback Voltage (CFB)

200

µA

50

Feedback-Amplifier Output Current

V/µs0.4Feedback-Amplifier Slew Rate

320 343 365

nA±100Feedback-Amplifier Input Bias Current

MHz1Feedback-Amplifier Unity-Gain Bandwidth

UNITSMIN TYP MAXPARAMETER

At preset DAC, CON = 0V, CADJ = 5V
(code = 15)

ns100CADJ, LADJ High Width (tSH)

ns0Reset Hold Time (tRH)

ns0Reset Setup Time (tRS)

ns110Reset Pulse Width (tR)

At preset DAC, LON = 0V, LADJ = 5V
(code = 31)

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

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

ns100CADJ, LADJ Low Width (tSL)

ns50

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

SD

)

At zero scale (code = 0)

At preset DAC, LON = 0V, LADJ = 5V
(code = 31)

At full scale (DAC code = 63)

610 635 660

905 938 971

mV

1210 1250 1290

MAX754 Feedback Voltage (LFB)

LCD CONTROLLER

TIMING (Note 2)

MAX753/MAX754

CCFL Backlight and
LCD Contrast Controllers

4 _______________________________________________________________________________________

______________________________________________________________Pin Description

Output of the CCFT Error AmplifierCC9

Connect to V

DD

CS10

Leave unconnectedCDRV11

Power Ground Connection for LDRVPGND12

Gate-Driver Output. Drives LCD backplane N-channel MOSFET.LDRV13

Digital Input for CCFT Brightness Adjustment. See Table 1.CADJ5

Analog GroundGND6

Reference Voltage Output, 1.25VREF7

Inverting Input for the CCFT Error AmplifierCFB8

Digital Input to Control CCFT Section. See Table 1.CON4

Digital Input to Control LCD Bias Section. See Table 1.LON3

PIN

Digital Input for LCD Backplane Bias Adjustment. See Table 1.LADJ2

5V Power-Supply InputV

DD

1

FUNCTIONNAME

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

_______________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 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

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.

MAX753/MAX754

CCFL Backlight and

LCD Contrast Controllers

_______________________________________________________________________________________ 5

MAX754CSE

MAX758ACWE

3,45

Q5

Q2

Q3

C4

C6

C8

C5

C7

Q4

C9

POSITIVE

CONTRAST

VOLTAGE

R10

2

61

812

T1

Q1

14

R1

C3C2

R16

LX

13

LDRV

12

PGND

16

LFB

6

GND

9

CC

2

LADJ

3

LON

5

D1B

CADJ

D1A

D2B

D2A

4

CON

10, 11

SS

GND

12, 13, 14

LX

7

L1

CS

10

V

DD

C1

1

CDRV

11

REF

7

CFB

8

SHDN

2

V+

1, 15, 16

REF

D5

3

CC

8

15

+5V, ±5%

UNREGULATED INPUT VOLTAGE

BATT

R2

R17

L2

D4

D3

D7B

D6B

D6A

D7A

+5V CMOS
LOGIC
CONTROL
SIGNALS

C10

R8

R4

R5

R6

R7

R18

R3

CCFL

Figure 1. CCFL and Positive LCD Power Supply