19-3321; Rev 0; 10/05
Low-Cost CCFL Backlight Controller
General Description
The MAX8722A integrated backlight controller is opti-
mized to drive cold-cathode fluorescent lamps (CCFLs)
using a full-bridge resonant inverter architecture.
Resonant operation maximizes striking capability and
provides near-sinusoidal waveforms over the entire
input range to improve CCFL lifetime. The controller
operates over a wide input voltage range (4.6V to 28V)
with high power to light efficiency. The device also
includes safety features that effectively protect against
many single-point fault conditions including lamp-out
and short-circuit faults.
The MAX8722A achieves 10:1 dimming range by “chop-
ping” the lamp current on and off using a digital pulse-
width modulation (DPWM) method. The DPWM frequency
can be accurately adjusted with a resistor or synchro-
nized to an external signal. The brightness is controlled
by an analog voltage on the CNTL pin. The device direct-
ly drives the four external n-channel power MOSFETs of
the full-bridge inverter. An internal 5.3V linear regulator
powers the MOSFET drivers, the DPWM oscillator, and
most of the internal circuitry. The MAX8722A is available
in a low-cost, 24-pin QSOP package and operates over a
-40°C to +85°C temperature range.
Features
♦
Synchronized to Resonant Frequency
Longer Lamp Life
Guaranteed Striking Capability
High Power to Light Efficiency
♦
Wide Input Voltage Range (4.6V to 28V)
♦
Input-Voltage Feed-Forward for Excellent Line
Rejection
♦
Accurate Dimming Control with Analog Interface
♦
10:1 Dimming Range
♦
Adjustable Accurate DPWM Frequency with Sync
Function
♦
Adjustable Lamp Current Rise and Fall Time
♦
Secondary Voltage Limit Reduces Transformer
Stress
♦
Lamp-Out Protection with Adjustable Timeout
♦
Secondary Overcurrent Protection with
Adjustable Timeout
♦
Low-Cost 24-Pin QSOP Package
MAX8722A
Ordering Information
PART
MAX8722AEEG
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
24 QSOP
PKG
CODE
E24-1
Applications
Notebook Computer Displays
LCD Monitors
LCD TVs
Minimal Operating Circuit
Pin Configuration
V
IN
V
CC
BATT
V
DD
TOP VIEW
BATT 1
SHDN 2
ILIM 3
TFLT 4
CNTL 5
DPWM 6
SYNC 7
FREQ 8
COMP 9
IFB 10
VFB 11
ISEC 12
24 GND
23 V
CC
22 V
DD
21 PGND
V
CC
GND
V
CC
BST2
BST1
GH1
ILIM
MAX8722A
LX1
LX2
FREQ
GL1
MAX8722A
20 GL2
19 GL1
18 GH1
PGND
17 LX1
16 BST1
15 BST2
14 LX2
13 GH2
SHDN
CNTL
SYNC
DPWM
COMP
TFLT
GL2
GH2
VFB
ISEC
IFB
QSOP
________________________________________________________________
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.
Low-Cost CCFL Backlight Controller
MAX8722A
ABSOLUTE MAXIMUM RATINGS
BATT to GND..........................................................-0.3V to +30V
BST1, BST2 to GND ...............................................-0.3V to +36V
BST1 to LX1, BST2 to LX2 ........................................-0.3V to +6V
CNTL, FREQ, SYNC, V
CC
, V
DD
to GND ...................-0.3V to +6V
COMP, DPWM, ILIM, TFLT to GND ............-0.3V to (V
CC
+ 0.3V)
GH1 to LX1 ..............................................-0.3V to (V
BST1
+ 0.3V)
GH2 to LX2 ..............................................-0.3V to (V
BST2
+ 0.3V)
GL1, GL2 to GND .......................................-0.3V to (V
DD
+ 0.3V)
IFB, ISEC, VFB to GND................................................-3V to +6V
SHDN
to GND...........................................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
24-Pin QSOP (derate 9.5mW/°C above +70°C)........761.9mW
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
(Circuit of Figure 1. V
BATT
= 12V, V
CC
= V
DD
, V
SHDN
= 5.3V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
BATT Input Voltage Range
BATT Quiescent Current
BATT 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, GL2 On-
Resistance, High
GH1, GH2, GL1, GL2 On-
Resistance, Low
GH1, GH2, GL1, GL2 Maximum
Output Current
BST1, BST2 Leakage Current
Resonant Frequency Range
Minimum Off-Time
Maximum Off-Time
Current-Limit Threshold
LX1 to PGND, LX2 to PGND
(Fixed)
Current-Limit Threshold
LX1 to PGND, LX2 to PGND
(Adjustable)
ILIM = V
CC
V
BST
_ = 12V, V
LX
_ = 7V
Guaranteed by design
30
340
24
180
470
33
200
I
TEST
= 10mA, V
CC
= V
DD
= 5.3V
I
TEST
= 10mA, V
CC
= V
DD
= 5.3V
V
CC
= V
DD
= V
BATT
V
CC
= V
DD
= open
V
SHDN
= V
CC
, V
IFB
= 1V
SHDN
= GND
V
SHDN
= 5.5V, 6V < V
BATT
< 28V,
0 < I
LOAD
< 10mA
SHDN
= GND, no load
V
CC
rising (leaving lockout)
V
CC
falling (entering lockout)
4.0
200
20
10
0.3
5
80
600
43
220
37
20
5.25
3.5
V
BATT
= 28V
V
BATT
= V
CC
= 5V
6
5.40
4.6
CONDITIONS
MIN
4.6
5.5
1
TYP
MAX
5.5
28.0
2
2
20
5.55
5.5
4.58
UNITS
V
mA
µA
V
V
V
mV
Ω
Ω
A
µA
kHz
ns
µs
mV
V
ILIM
= 0.5V
V
ILIM
= 2.0V
80
370
100
400
120
mV
430
2
_______________________________________________________________________________________
Low-Cost CCFL Backlight Controller
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1. V
BATT
= 12V, V
CC
= V
DD
, V
SHDN
= 5.3V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
Zero-Current Crossing Threshold
LX1 to GND, LX2 to GND
Current-Limit Leading Edge
Blanking
IFB Input Voltage Range
IFB Regulation Point
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
DPWM Rising to Falling Ratio
ISEC Overcurrent Threshold
ISEC Input Bias Current
VFB Input Bias Current
VFB Overvoltage Threshold
R
FREQ
= 100kΩ
DPWM Chopping Frequency
DPWM Input Low Voltage
DPWM Input High Voltage
DPWM Input Hysteresis
DPWM Input Bias Current
DPWM Output Low Resistance
DPWM Output High Resistance
SYNC Input Low Voltage
SYNC Input High Voltage
SYNC Input Hysteresis
SYNC Input Bias Current
SYNC Input Frequency Range
CNTL Minimum Duty-Cycle
Threshold
CNTL Maximum Duty-Cycle
Threshold
CNTL Input Current
DPWM ADC Resolution
0 < V
CNTL
< V
CC
Guaranteed monotonic
V
SYNC
= 2V
-0.3
10
0.20
1.9
-0.1
5
0.23
2.0
2.1
100
+0.3
50
0.26
2.1
+0.1
R
FREQ
= 169kΩ
R
FREQ
= 340kΩ
SYNC = V
CC
, R
FREQ
= 169kΩ
SYNC = V
CC
, R
FREQ
= 169kΩ
SYNC = V
CC
, R
FREQ
= 169kΩ
SYNC = V
CC
, R
FREQ
= 169kΩ
SYNC = GND, FREQ = V
CC
SYNC = V
CC
, FREQ = V
CC
-0.3
2.1
100
+0.3
2.4
2.4
0.8
204
0 < V
ISEC
< 2V
-4V < V
VFB
< +4V
V
IFB
= 800mV, V
ISEC
= 2V
CNTL = GND, V
COMP
= 2V
V
IFB
= 0
1.15
-0.3
-25
2.2
2.3
343
209
106
0.8
V
V
mV
µA
kΩ
kΩ
V
V
mV
µA
kHz
V
V
µA
Bits
214
Hz
0.5V < V
COMP
< 4V
0 < V
IFB
< 2V
-2V < V
IFB
< 0
CONDITIONS
MIN
1
240
-2
770
-2
-150
560
60
7
600
100
10
1200
100
2.5
1.21
1.28
+0.3
+25
2.4
640
160
18
790
TYP
6
350
MAX
12
460
+2
810
+2
UNITS
mV
ns
V
mV
µA
mV
µS
MΩ
µA
µA
—
V
µA
µA
V
MAX8722A
_______________________________________________________________________________________
3
Low-Cost CCFL Backlight Controller
MAX8722A
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1. V
BATT
= 12V, V
CC
= V
DD
, V
SHDN
= 5.3V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
SHDN
Input Low Voltage
SHDN
Input High Voltage
SHDN
Input Bias Current
FREQ Dual Mode™ Input High
Level
FREQ Input Regulation Level
FREQ Input Bias Current
TFLT Charge Current
TFLT Trip Threshold
FREQ = V
CC
V
ISEC
< 1.25V and V
IFB
< 600mV; V
FLT
= 2V
V
ISEC
< 1.25V and V
IFB
> 600mV; V
FLT
= 2V
V
ISEC
> 1.25V and V
IFB
< 600mV; V
FLT
= 2V
3.95
0.95
2.1
-1
V
CC
-
0.35
V
CC
/ 2
230
1.00
-1
116
4.10
4.20
V
1.05
µA
+1
CONDITIONS
MIN
TYP
MAX
0.8
UNITS
V
V
µA
V
V
µA
Dual Mode is a trademark of Maxim Integrated Products, Inc.
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1. V
BATT
= 12V, V
CC
= V
DD
, V
SHDN
= 5.3V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 1)
PARAMETER
BATT Input Voltage Range
BATT Quiescent Current
BATT Quiescent Current,
Shutdown
V
CC
Output Voltage, Normal
Operation
V
CC
Output Voltage, Shutdown
V
CC
Undervoltage-Lockout
Threshold
GH1, GH2, GL1, GL2 On-
Resistance, High
GH1, GH2, GL1, GL2 On-
Resistance, Low
BST1, BST2 Leakage Current
Resonant Frequency Range
Minimum Off-Time
Maximum Off-Time
Current-Limit Threshold
LX1 - PGND, LX2 - PGND (Fixed)
ILIM = V
CC
V
CC
= V
DD
= V
BATT
V
CC
= V
DD
= open
V
SHDN
= V
CC
, V
IFB
= 1V
SHDN
= GND
V
SHDN
= 5.5V, 6V < V
BATT
< 28V
0 < I
LOAD
< 20mA
SHDN
= GND, no load
V
CC
rising (leaving lockout)
V
CC
falling (entering lockout)
I
TEST
=10mA, V
CC
= V
DD
= 5.3V
I
TEST
=10mA, V
CC
= V
DD
= 5.3V
V
BST
_ = 12V, V
LX
_ = 7V
Guaranteed by design
30
340
24
180
4.0
37
20
5
80
600
43
220
5.25
3.5
V
BATT
= 28V
V
BATT
= V
CC
= 5V
CONDITIONS
MIN
4.6
5.5
TYP
MAX
5.5
28.0
2
2
20
5.55
5.5
4.58
UNITS
V
mA
µA
V
V
V
Ω
Ω
µA
kHz
ns
µs
mV
4
_______________________________________________________________________________________
Low-Cost CCFL Backlight Controller
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1. V
BATT
= 12V, V
CC
= V
DD
, V
SHDN
= 5.3V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 1)
PARAMETER
Current-Limit Threshold
LX1 - PGND, LX2 - PGND
(Adjustable)
Zero-Current Crossing Threshold
LX1 - GND, LX2 - GND
Current-Limit Leading Edge
Blanking
IFB Input Voltage Range
IFB Regulation Point
IFB Input Bias Current
IFB Lamp-Out Threshold
IFB to COMP Transconductance
COMP Output Impedance
ISEC Overcurrent Threshold
VFB Overvoltage Threshold
DPWM Chopping Frequency
DPWM Input Low Voltage
DPWM Input High Voltage
DPWM Output Low Resistance
DPWM Output High Resistance
SYNC Input Low Voltage
SYNC Input High Voltage
SYNC Input Bias Current
SYNC Input Frequency Range
CNTL Minimum Duty-Cycle
Threshold
CNTL Maximum Duty-Cycle
Threshold
SHDN
Input Low Voltage
SHDN
Input High Voltage
FREQ Dual-Mode Input High
Level
TFLT Trip Threshold
2.1
V
CC
-
0.35
3.95
4.20
V
SYNC
= 2V
2.1
-0.3
10
0.20
1.9
+0.3
50
0.26
2.1
0.8
R
FREQ
= 169kΩ
SYNC = V
CC
, R
FREQ
= 169kΩ
SYNC = V
CC
, R
FREQ
= 169kΩ
SYNC = GND, FREQ = V
CC
SYNC = V
CC
, FREQ = V
CC
2.1
2.4
2.4
0.8
0.5V < V
COMP
< 4V
0 < V
IFB
< 2V
-2V < V
IFB
< 0
V
ILIM
= 0.5V
V
ILIM
= 2.0V
CONDITIONS
MIN
80
370
1
240
-2
770
-2
-150
560
60
7
1.15
2.2
200
640
160
18
1.28
2.4
218
0.8
TYP
MAX
120
mV
430
12
460
+2
810
+2
mV
ns
V
mV
µA
mV
µS
MΩ
V
V
Hz
V
V
kΩ
kΩ
V
V
µA
kHz
V
V
V
V
V
V
UNITS
MAX8722A
Note 1:
Specifications to -40°C are guaranteed by design based on final characterization results.
_______________________________________________________________________________________
5
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