EVALUATION KIT AVAILABLE
MAX8751
Fixed-Frequency, Full-Bridge CCFL
Inverter Controller
General Description
The MAX8751 cold-cathode-fluorescent lamp (CCFL)
inverter controller is designed to drive multiple CCFLs
using the fixed-frequency, full-bridge inverter topology. The
MAX8751 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 MAX8751 can drive large power MOSFETs typically
used in applications where one power stage drives four
or more CCFL lamps in parallel. An internal 5.35V linear
regulator powers the MOSFET drivers and most of the
internal circuitry. The controller operates over a wide
input-voltage range (6V to 28V) with high power to light
efficiency. The device also includes safety features that
effectively protect against many single-point fault condi-
tions, including lamp-out and short-circuit conditions.
The MAX8751 achieves a 10:1 dimming range by “chop-
ping” the lamp current on and off using the digital pulse-
width modulation (DPWM) method. The DPWM frequency
can be accurately adjusted with a resistor or synchronized
to an external signal. The brightness is controlled by an
analog voltage on the CNTL pin.
The MAX8751 is capable of synchronizing and adjusting the
phase of the gate drivers and DPWM oscillator. These fea-
tures allow multiple MAX8751 ICs to be connected in a daisy-
chain configuration. The switching frequency and DPWM
frequency 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 oscilla-
tors and keeps operating. Phase-shift select pins PS1 and
PS2 can be used to program up to four different phase shifts,
allowing up to five MAX8751s to be used together.
The MAX8751 is available in a low-profile, 32-pin TQFN
package and operates over the -40°C to +85°C tempera-
ture range.
Features
● All n-Type MOSFET Low-Cost, Full-Bridge, Fixed-
Frequency Inverter Topology for Highest Efficiency
● Resonant-Mode Striking Ensures Startup
● Strong Gate Drivers Can Easily Drive Large External
MOSFETs for Multilamp Applications
● Adjustable DPWM Frequency with Sync and Phase-
Shift Capability
● 10:1 Dimming Range with Accurate Analog Interface
● Lamp-Out Detection with Adjustable Timeout
● Secondary Current Limit with Adjustable Timeout
● Adjustable Secondary Voltage Limiting
● Adjustable DPWM Rise and Fall Time
● Wide Input Voltage Range (6V to 28V)
● 32-Pin TQFN Package
Minimal Operating Circuit
VIN
7V TO 24V
3A
GND
IN
GND
V
CC
V
CC
MAX8751
SEL
GH1
BST1
ON/OFF
BRIGHTNESS
SHDN
CNTL
PCOMP
LX1
LX2
BST2
GL1
PGND1
HF
PGND2
GL2
LF
HFCK
HSYNC
LSYNC
LFCK
VFB
GH2
ISEC
CCFL
T1
Applications
● LCD TVs
● LCD Monitors
● Notebook Computers
DPWM
IFB
PSCK
PS1
PS2
COMP
TFLT
Ordering Information
PART
MAX8751ETJ
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
32 TQFN
Pin Configuration appears at end of data sheet.
19-3784; Rev 1; 5/14
MAX8751
Fixed-Frequency, Full-Bridge CCFL
Inverter Controller
Absolute Maximum Ratings
IN, LX1, LX2 to GND...............................................-0.3V to +30V
BST1, BST2 to GND ...............................................-0.3V to +36V
BST2 to LX2..............................................................-0.3V to +6V
V
CC
to GND..............................................................-0.3V to +6V
GH1 to LX1...............................................-0.3V to V
BST1
+ 0.3V
GH2 to LX2...............................................-0.3V to V
BST2
+ 0.3V
CNTL, SEL COMP, GL1, GL2, DPWM,
HF, LF, HFCK, HSYNC, LSYNC, LFCK, PCOMP, PS1, PSCK,
TFLT, PS2,
SHDN
to GND.......................-0.3V to V
CC
+ 0.3V
IFB, ISEC, VFB to GND...............................................-6V to +6V
PGND1, PGND2 to GND ..........................................-0.3V to +3V
Continuous Power Dissipation (T
A
= +70°C)
32-Pin TQFN (derate 21.3mW/°C above +70°C)....1702.1mW
Operating Temperature Range.............................-40°C to +85°C
Junction Temperature.......................................................+150°C
Storage Temperature Range .............................-65°C to +160°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
= 24V,
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
GH1, GH2, GL1, and GL2
On-Resistance, Low State
GH1, GH2, GL1, and GL2
On-Resistance, High State
BST1, BST2 Leakage Current
Resonant Frequency Range
Minimum Off-Time
Maximum Off-Time
Current-Limit Threshold;
LX1 - GND, LX2 - GND
Zero-Crossing Threshold:
LX1 - GND, LX2 - GND
IFB Maximum AC Voltage
Current-Limit Leading Edge Blanking
IFB Regulation Point
IFB Input Bias Current
Internally full-wave rectified
0 < V
IFB
< 2V
-2V < V
IFB
< 0
240
770
-3
-150
I
TEST
= 10mA; V
CC
= 5.3V
I
TEST
= 10mA; V
CC
= 5.3V
V
BST1
= 24V, V
LX1
= 19V; V
BST2
= 24V,
V
LX2
= 19V
Not tested
30
240
20
380
5
360
30
400
10
Q3
360
790
480
810
+3
V
SHDN
= 5.5V, V
IN
= 28V
V
SHDN
= 0V
V
SHDN
= 5.5V, 6V < V
IN
< 28V,
0 < I
LOAD
< 20mA
V
SHDN
= 0V, no load
V
CC
rising (leaving lockout)
V
CC
falling (entering lockout)
4.0
200
1
4
3
8
5
80
480
40
420
15
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
V
ns
mV
µA
www.maximintegrated.com
Maxim Integrated │ 2
MAX8751
Fixed-Frequency, Full-Bridge CCFL
Inverter Controller
Electrical Characteristics (continued)
(V
IN
= 24V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
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 Bias Current
ISEC Overcurrent Threshold
VFB Input Bias Current
VFB Overvoltage Threshold
Main Oscillator Frequency
Main Oscillator Frequency Range
HF, LF, HFCK, LFCK Input-Low Voltage
HF, LF, HFCK, LFCK Input-High Voltage
HF, LF, HFCK, LFCK Input Hysteresis
HF, LF, HFCK, LFCK
Input Bias Current
HF Input-Frequency Range
HF, LF, HFCK, LFCK
Input Rise and Fall Time
HSYNC, LSYNC Input-Low Voltage
HSYNC, LSYNC Input-High Voltage
HSYNC, LSYNC Input Hysteresis
HSYNC, LSYNC Input Bias Current
HSYNC Input Frequency Range
HSYNC, LSYNC Input Rise and Fall Time
DPWM Chopping Frequency
DPWM Chopping Frequency Range
R
LF
= 150kΩ
202
80
208
-1
190
2.1
100
+1
460
200
214
300
Slave mode, V
CNTL
= V
CC
Slave mode, V
CNTL
= V
CC
Slave mode, V
CNTL
= V
CC
Slave mode, V
CNTL
= V
CC
Slave mode, V
CNTL
= V
CC
Slave mode, V
CNTL
= V
CC
-1
20
RHF = 100kΩ
-4V < V
VFB
< +4V
V
IFB
= 800mV, V
ISEC
= 2.5V
CNTL = GND, V
COMP
= 1.5V
-0.3
1.18
-25
2.10
52.2
20
2.1
100
+1
100
200
0.8
2.25
53.8
1.22
CONDITIONS
Reject 1µs glitches
1V < V
COMP
< 2.5V
MIN
730
TYP
780
100
10
1200
100
+0.3
1.26
+25
2.40
55.4
100
0.8
MAX
830
UNITS
mV
µS
MΩ
µA
µA
µA
V
µA
V
kHz
kHz
V
V
mV
µA
kHz
ns
V
V
mV
µA
kHz
ns
Hz
Hz
www.maximintegrated.com
Maxim Integrated │ 3
MAX8751
Fixed-Frequency, Full-Bridge CCFL
Inverter Controller
Electrical Characteristics (continued)
(V
IN
= 24V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
LF Input Frequency Range
LSYNC Input Frequency Range
HFCK Input Frequency Range
HFCK, LFCK, PSCK, DPWM Output On-
Resistance
LFCK Input Frequency Range
CNTL Minimum Duty-Cycle Threshold
CNTL Maximum Duty-Cycle Threshold
CNTL Input Current
CNTL Input Threshold
DPWM Dimming Resolution
SEL, PS1, PS2
Input-Low Voltage
SEL, PS1, PS2
Input-High Voltage
SEL, PS1, PS2
Input Hysteresis
SHDN
Input-Low Voltage
SHDN
Input-High Voltage
SEL, PS1, PS2 Input Bias Current
SHDN
Input Bias Current
V
ISEC
< 1.25 and V
IFB
< 790mV,
V
FLT
= 2.0V
TFLT Charging Current
V
ISEC
< 1.25 and V
IFB
< 790mV,
V
FLT
= 2.0V
V
ISEC
< 1.25 and V
IFB
< 790mV,
V
FLT
= 2.0V
TFLT Trip Threshold
3.85
SEL, PS1, PS2 input-high voltage
SEL, PS1, PS2 input hysteresis
2.1
-1
-1
0.95
1.00
-1
126
4.00
4.15
V
+1
+1
1.05
µA
2.1
100
0.8
0 < V
CNTL
< 2V
Slave mode
Guaranteed monotonic
R
LF
= 150kΩ
Slave mode, V
CNTL
= V
CC
(Note 1)
I
TEST
= 1mA
Slave mode, V
CNTL
= V
CC
10.24
0.21
1.9
-0.1
4.2
4.5
7
0.8
0.23
2.0
CONDITIONS
Slave mode, V
CNTL
= V
CC
MIN
80
120
120
TYP
MAX
300
280
600
2.4
38.40
0.26
2.1
+0.1
4.9
UNITS
Hz
Hz
kHz
kΩ
kHz
V
V
V
V
Bits
V
V
mV
mV
V
µA
µA
www.maximintegrated.com
Maxim Integrated │ 4
MAX8751
Fixed-Frequency, Full-Bridge CCFL
Inverter Controller
Electrical Characteristics
(V
IN
= 24V,
T
A
= -40°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
GH1, GH2, GL1, and GL2
On-Resistance, Low State
GH1, GH2, GL1, and GL2
On-Resistance, High State
Minimum Off-Time
Maximum Off-Time
Current-Limit Threshold: LX1 - GND, LX2 -
GND
Zero-Crossing Threshold: LX1 - GND, LX2 -
GND
Current-Limit Leading-Edge Blanking
IFB Lamp-Out Threshold
IFB Regulation Point
ISEC Overcurrent Threshold
VFB Overvoltage Threshold
Main Oscillator Frequency
R
HF
= 100kΩ
Reject 1µs glitches
V
SHDN
= 5.5V, V
IN
= 28V
V
SHDN
= 0
V
SHDN
= 5.5V, 6V < V
IN
< 28V,
0 < I
LOAD
< 20mA
V
SHDN
= 0, no load
V
CC
rising (leaving lockout)
V
CC
falling (entering lockout)
I
TEST
= 10mA, V
CC
= 5.3V
I
TEST
= 10mA, V
CC
= 5.3V
240
20
380
5
240
730
755
1.16
2.10
51.7
4.0
3
8
480
40
420
15
480
830
820
1.26
2.40
55.9
5.20
3.50
CONDITIONS
MIN
6
TYP
MAX
28
6
20
5.50
5.50
4.5
UNITS
V
mA
µA
V
V
V
Ω
Ω
ns
µs
mV
mV
ns
mV
mV
V
V
kHz
www.maximintegrated.com
Maxim Integrated │ 5
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