EVALUATION KIT AVAILABLE
MAX8729
Constant-Frequency, Half-Bridge CCFL
Inverter Controller
General Description
The MAX8729 cold-cathode-fluorescent lamp (CCFL)
inverter controller is designed to drive multiple CCFLs
using the half-bridge inverter consisting of two external
n-channel power MOSFETs. The half-bridge topology
minimizes the component count, while providing near
sinusoidal drive waveforms. The MAX8729 operates
in resonant mode during striking and switches over to
constant-frequency operation after all the lamps are lit.
This unique feature ensures reliable striking under all
conditions and reduces the transformer stress.
The MAX8729 provides accurate lamp-current regulation
(±2.5%). The lamp current is adjustable with an external
resistor. The MAX8729 changes the brightness by turning
the CCFL on and off using a digital pulse-width modul-
tion (DPWM) method, while maintaining the lamp current
constant. The brightness can be adjusted with an analog
voltage on the CNTL pin, or with an external PWM signal.
The MAX8729 is capable of synchronizing and adjusting
the phase of the gate drivers and DPWM oscillator. These
features allow multiple MAX8729 ICs to be connected in
a daisy-chain configuration. The switching frequency and
DPWM frequency of the master IC can be easily adjusted
using external resistors, or synchronized with system
signals. If the controller loses the external sync signals, it
switches over to the internal oscillators and keeps opera
ing. Phase-shift select pins PS1 and PS2 can be used
to program four different phase shifts, allowing up to five
MAX8729s to be used together.
The MAX8729 protects the inverter from lamp-out, sec-
ondary overvoltage, and secondary short-circuit faults.
The MAX8729 can drive large-power MOSFETs typically
used in applications where one power stage drives four
or more CCFL tubes in parallel. An internal 5.35V linear
regulator powers the MOSFET drivers and most of the
internal circuitry. The MAX8729 is available in a low-cost,
28-pin QSOP package and operates over the -40°C to
+85°C extended temperature range.
Features
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Low-Cost, Half-Bridge Inverter Topology
Resonant Mode Striking Ensures Startup
Constant-Frequency Operation After Lamp Ignition
Drives Large External MOSFETs
Supports Multilamp Applications
Sync and Phase-Shift Controls Allow Daisy- Chained
Operation
Adjustable Switching Frequency and DPWM
Frequency
±2.5% Lamp-Current Regulation
10:1 Dimming Range
Accurate Analog-Dimming Control
Lamp-Out Detection with Adjustable Timeout
Secondary Current and Voltage Limiting
Primary Current Limit with R
DS(ON)
Sensing
Adjustable DPWM Rise and Fall Time
Low-Cost, 28-Pin QSOP Package
Simplified Operating Circuit
INPUT
VCC
3 IN
5 GND
VCC
ON/OFF
DIMMING
4 V
CC
V
DD
28
BST 25
GH 24
LX 23
GL 27
PGND 26
VFB 19
ISEC 20
8 SHDN
7 CNTL
2 SEL
12 PSCK
22 PS1
16 PS2
15 HF
CCFL
IFB 18
COMP 17
Applications
●
LCD Monitors
●
LCD TVs
MAX8729
●
Notebook Computers
9 LF
TFLT 6
Ordering Information
PART
MAX8729EEI
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
28 QSOP
11 DPWM
13 HFCK
10
LFCK
PCOMP 1
HSYNC 14
LSYNC 21
Pin Configuration appears at end of data sheet.
19-3754; Rev 1; 4/14
MAX8729
Constant-Frequency, Half-Bridge CCFL
Inverter Controller
Absolute Maximum Ratings
IN, LX to GND .......................................................-0.3V to +30V
BST to GND ..........................................................-0.3V to +36V
BST to LX ................................................................-0.3V to +6V
V
CC
, V
DD
to GND ...................................................-0.3V to +6V
GH to LX.................................................... -0.3V to V
BST
+ 0.3V
CNTL, COMP, GL, DPWM, HF, LF, HFCK,
LFCK, HSYNC, LSYNC, PS1, PS2, PSCK, TFLT,
PCOMP, SEL ...........................................-0.3V to V
CC
+ 0.3V
IFB, ISEC, VFB to GND .............................................-6V to +6V
SHDN
to GND .........................................................-0.3V to +6V
PGND to GND ......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
28-Pin QSOP (derate 10.8mW/°C above +70°C) ....860.2mW
Operating Temperature Range ........................... -40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range ............................ -65°C to +150°C
Lead Temperature (soldering, 10s) ................................. +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
IN
= 12V, V
DD
= 5.3V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
IN Input Voltage Range
IN Quiescent Current
IN Quiescent Current, Shutdown
V
CC
Output Voltage, Normal
Operation
V
CC
Output Voltage, Shutdown
V
CC
Undervoltage
Lockout Threshold
V
CC
Undervoltage-Lockout
Hysteresis
GH, GL On-Resistance, Low State
GH, GL On-Resistance, High State
BST Leakage Current
Resonant Frequency Range
Minimum Off-Time
Maximum Off-Time (LX-GND)
Low-Side MOSFET Maximum Current-
Limit Threshold (LX-GND)
High-Side MOSFET Maximum
Current-Limit Threshold (IN – LX)
Low-Side MOSFET Zero-Current-
Crossing Threshold (GND – LX)
High-Side MOSFET Zero-Current-
Crossing Threshold (LX – IN)
Current-Limit Leading Edge Blanking
IFB Regulation Point
IFB Maximum AC Voltage
Internally full-wave rectified
I
TEST
= 10mA
I
TEST
= 10mA
V
BST
= 17V, V
LX
= 12V
Not tested
30
330
24.0
370
370
0
-16
310
770
416
30.7
400
400
10
+6
410
790
±3
V
SHDN
= 5.3V, V
IN
= 28V
SHDN
= GND
V
SHDN
= 5.3V, 6V < V
IN
< 28V,
0 < I
LOAD
< 10mA
SHDN
= GND, no load
V
CC
rising (leaving lockout)
V
CC
falling (entering lockout)
4.0
200
1
4
2
6
5
80
560
42.0
470
470
18
+28
560
810
5.20
3.5
CONDITIONS
MIN
6
3.2
6
5.35
4.6
TYP
MAX
28
6
20
5.50
5.5
4.5
UNITS
V
mA
µA
V
V
V
mV
Ω
Ω
µA
kHz
ns
µs
mV
mV
mV
mV
ns
mV
V
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2
MAX8729
Constant-Frequency, Half-Bridge CCFL
Inverter Controller
Electrical Characteristics (continued)
(V
IN
= 12V, V
DD
= 5.3V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
IFB Input Bias Current
IFB Lamp-Out Threshold
IFB-to-COMP Transconductance
COMP Output Impedance
COMP Discharge Current During
Overvoltage or Overcurrent Fault
COMP Discharge Current During
DPWM Off-Time
ISEC Input Voltage Range
ISEC Input Bias Current
ISEC Overcurrent Threshold
VFB Input-Voltage Range
VFB Input Bias Current
VFB Overvoltage Threshold
Main Oscillator Frequency
Main Oscillator Frequency Range
HF, HFCK, LF, LFCK Input-Low
Voltage
HF, HFCK, LF, LFCK Input-High
Voltage
Slave mode, V
CNTL
= V
CC
Slave mode, V
CNTL
= V
CC
2.1
200
-1
+1
200
20
120
190
80
10.24
120
199
80
207
100
600
460
300
38.40
280
215
300
R
HF
= 100kΩ
-4V < V
VFB
< 4V
V
IFB
= 800mV, V
ISEC
= 2.5V
CNTL = GND, V
COMP
= 1.5V
-3
-0.3
1.18
-4
-25
2.15
51.7
20
2.25
53.8
1.21
0 < V
IFB
< 2V
-2V < V
IFB
< 0
Reject 1µs glitches
0.5V < V
COMP
< 4V
CONDITIONS
MIN
-3
-150
760
790
100
10
1200
100
+3
+0.3
1.26
+4
+25
2.35
55.9
100
0.8
820
TYP
MAX
+3
UNITS
µA
mV
µS
MΩ
µA
µA
V
µA
V
V
µA
V
kHz
kHz
V
V
mV
µA
ns
kHz
kHz
kHz
Hz
kHz
Hz
Hz
Hz
HF, HFCK, LF, LFCK Input Hysteresis Slave mode, V
CNTL
= V
CC
HF, HFCK, LF, LFCK Input Bias
Current
HF, HFCK, LF, LFCK Input Rise and
Fall Time
HF Input-Frequency Range
HFCK Input Frequency Range
HSYNC Input Frequency Range
LF Input Frequency Range
LFCK Input Frequency Range
LSYNC Input Frequency Range
DPWM Chopping Frequency
DPWM Frequency Range
Slave mode, V
CNTL
= V
CC
Slave mode, V
CNTL
= V
CC
Slave mode, V
CNTL
= V
CC
Slave mode, V
CNTL
= V
CC
R
HF
= 100kΩ
Slave mode, V
CNTL
= V
CC
Slave mode, V
CNTL
= V
CC
R
LF
= 150kΩ
R
LF
= 150kΩ
R
LF
= 300kΩ
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Maxim Integrated
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3
MAX8729
Constant-Frequency, Half-Bridge CCFL
Inverter Controller
Electrical Characteristics (continued)
(V
IN
= 12V, V
DD
= 5.3V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
PS1, PS2, LSYNC, HSYNC, SEL
Input Low Voltage
PS1, PS2, LSYNC, HSYNC, SEL
Input High Voltage
PS1, PS2, LSYNC, HSYNC, SEL
Input Hysteresis
PS1, PS2, LSYNC, HSYNC, SEL
Input Bias Current
HFCK, LFCK, PSCK, DPWM Output
On-Resistance
CNTL Minimum Duty-Cycle
Threshold
CNTL Maximum Duty-Cycle
Threshold
CNTL Input Current
CNTL Input Threshold
DPWM A/D Converter Resolution
SHDN
Input Low Voltage
SHDN
Input High Voltage
SHDN
Input Bias Current
V
ISEC
< 1.25 and V
IFB
< 790mV; V
FLT
= 2.0V
TFLT Charging Current
TFLT Trip Threshold
V
ISEC
< 1.25 and V
IFB
> 790mV; V
FLT
= 2.0V
V
ISEC
> 1.25 and V
IFB
< 790mV; V
FLT
= 2.0V
3.9
2.1
-1
0.95
1.00
-1
126
4.0
4.1
V
+1
1.05
µA
0 < V
CNTL
< 2V
Slave mode
Guaranteed monotonic
I
TEST
= 1mA
0.21
1.9
-0.1
4.2
4.5
5
0.8
0.23
2.0
-1
2.1
200
+1
2.5
0.26
2.1
+0.1
4.8
CONDITIONS
MIN
TYP
MAX
0.8
UNITS
V
V
mV
µA
kΩ
V
V
µA
V
Bits
V
V
µA
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MAX8729
Constant-Frequency, Half-Bridge CCFL
Inverter Controller
Electrical Characteristics
(V
IN
= 12V, V
DD
= 5.3V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 1)
PARAMETER
IN Input-Voltage Range
IN Quiescent Current
IN Quiescent Current, Shutdown
V
CC
Output Voltage, Normal
Operation
V
CC
Output Voltage, Shutdown
V
CC
Undervoltage
Lockout Threshold
GH, GL On-Resistance, Low State
GH, GL On-Resistance, High State
Minimum Off-Time
Maximum Off-Time
Low-Side MOSFET Maximum
Current-Limit Threshold (LX – GND)
High-Side MOSFET Maximum
Current-Limit Threshold (IN – LX)
Low-Side MOSFET Zero-Current
Crossing Threshold (GND – LX)
High-Side MOSFET Zero-Current
Crossing Threshold (LX – IN)
Current-Limit Leading-Edge Blanking
IFB Regulation Point
IFB Maximum AC Voltage
IFB Input Bias Current
IFB Lamp-Out Threshold
ISEC Input Voltage Range
ISEC Overcurrent Threshold
VFB Input Voltage Range
VFB Overvoltage Threshold
Main Oscillator Frequency
Main Oscillator Frequency Range
R
HF
= 100kΩ
0 < V
IFB
< 2V
-2V < V
IFB
< 0
Reject 1µs glitches
-3
-150
760
-3
1.18
-4
2.15
50.0
20
820
+3
1.26
+4
2.35
57.6
100
Internally full-wave rectified
V
SHDN
= 5.3V, V
IN
= 28V
SHDN
= GND
V
SHDN
= 5.3V, 6V < V
IN
< 28V,
0 < I
LOAD
< 10mA
SHDN
= GND, no load
V
CC
rising (leaving lockout)
V
CC
falling (entering lockout)
I
TEST
= 10mA
I
TEST
= 10mA
330
24.0
350
350
0
-16
310
770
±3
+3
4.0
3
7
560
42.0
500
500
18
+28
560
810
5.20
3.5
CONDITIONS
MIN
6
TYP
MAX
28
6
20
5.50
5.5
4.5
UNITS
V
mA
µA
V
V
V
Ω
Ω
ns
µs
mV
mV
mV
mV
ns
mV
V
µA
mV
V
V
V
V
kHz
kHz
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