19-0768; Rev 0; 3/07
High-Efficiency CCFL Backlight
Controller with SMBus Interface
General Description
The MAX8709B integrated backlight controller is
optimized to drive cold-cathode fluorescent lamps
(CCFLs) using a resonant full-bridge inverter architecture.
The 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 of 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 MAX8709B achieves 10:1 dimming range by “chop-
ping” the lamp current on and off using a digital pulse-
width-modulation (DPWM) method. The minimum DPWM
duty cycle of the MAX8709B is 12.5%. The brightness is
controlled with a 2-wire SMBus™-compatible interface.
The device directly 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
MAX8709B is available in a space-saving 28-pin
thin QFN 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)
♦
Feed Forward for Excellent Line Rejection
♦
SMBus Dimming Control Interface
♦
10:1 Dimming Range
♦
Guaranteed 200Hz to 220Hz DPWM Frequency
♦
Secondary Voltage Limit Reduces Transformer
Stress
♦
Adjustable Lamp-Out Protection with 1s Timer
♦
Secondary Current Limit Protects Against High-
Voltage Short Circuits to Ground
♦
Small, 5mm x 5mm, Thin QFN Package
MAX8709B
Ordering Information
PART
MAX8709BETI
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
28 Thin QFN 5mm x 5mm
Applications
Notebook Computer Displays
LCD Monitors
SMBus is a trademark of Intel Corp.
LCD TVs
Automotive Displays
Pin Configuration appears at end of data sheet.
Minimal Operating Circuit
V
IN
BATT
V
CC
V
DD
BST2
LOT
REF
BST1
GH1
GND
MAX8709B
LX1
ILIM
LX2
GL1
CCV
CCI
PGND
GL2
SUS
SDA
SCL
GH2
VFB
ISEC
IFB
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
High-Efficiency CCFL Backlight
Controller with SMBus Interface
MAX8709B
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
GH1 to LX1 ..............................................-0.3V to (V
BST1
+ 0.3V)
GH2 to LX2 ..............................................-0.3V to (V
BST2
+ 0.3V)
V
CC
, V
DD
to GND .....................................................-0.3V to +6V
REF, ILIM to GND .......................................-0.3V to (V
CC
+ 0.3V)
GL1, GL2 to GND .......................................-0.3V to (V
DD
+ 0.3V)
CCI, CCV, LOT to GND ............................................-0.3V to +6V
IFB, ISEC, VFB to GND................................................-6V to +6V
SDA, SCL, SUS to GND............................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
28-Pin Thin QFN (derate 20.84mW/°C above +70°C) ..1667mW
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
LOT
= V
REF
, V
CC
= V
DD,
V
SUS
= 5.3V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C,
unless otherwise noted.)
PARAMETER
V
BATT
Input Voltage Range
V
BATT
Quiescent Current
V
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
V
CC
Power-On Reset (POR) Threshold
V
CC
POR Hysteresis
REF Output Voltage, Normal Operation
GH1, GH2, GL1, GL2 On-Resistance
GH1, GH2, GL1, GL2 Output Current
BST1, BST2 Leakage Current
Input Resonant Frequency
Minimum Off-Time
Maximum Off-Time
Current-Limit Threshold
LX1 - GND, LX2 - GND (Fixed)
Current-Limit Threshold
LX1 - GND, LX2 - GND (Adjustable)
Minimum Current Threshold
LX1 - GND, LX2 - GND
ILIM = V
CC
V
ILIM
= 0.5V
V
ILIM
= 2.0V
V
BST
_ = 12V, V
LX
_ = 7V
Guaranteed by design
25
180
18
180
80
370
280
28
200
100
400
6
4.5V < V
CC
< 5.5V, I
LOAD
= 40µA
I
TEST
= 100mA, V
CC
= V
DD
= 5.3V
1.96
Rising edge
0.90
CONDITIONS
V
CC
= V
DD
= V
BATT
V
CC
= V
DD
= open
V
SUS
= 5.5V
SUS = GND
V
SUS
= 5.5V, 6V < V
BATT
< 28V,
0 < I
LOAD
< 20mA
SUS = GND, no load
V
CC
rising (leaving lockout)
V
CC
falling (entering lockout)
4.0
200
1.75
50
2.00
9
0.5
5
300
380
38
220
120
430
2.04
18
2.70
5.0
3.5
V
BATT
= 28V
V
BATT
= V
CC
= 5V
6
5.35
4.6
MIN
4.6
5.5
1.5
TYP
MAX
5.5
28.0
3
3
20
5.5
5.5
4.5
UNITS
V
mA
µA
V
V
V
mV
V
mV
V
Ω
A
µA
kHz
ns
µs
mV
mV
mV
2
_______________________________________________________________________________________
High-Efficiency CCFL Backlight
Controller with SMBus Interface
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1. V
BATT
= 12V, V
LOT
= V
REF
, V
CC
= V
DD,
V
SUS
= 5.3V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C,
unless otherwise noted.)
PARAMETER
LOT Input Voltage Range
LOT Input Bias Current
IFB Input Voltage Range
IFB Regulation Point
IFB Input Bias Current
IFB Lamp-Out Threshold
IFB to CCI Transconductance
CCI Output Impedance
ISEC Input Voltage Range
ISEC Regulation Threshold
ISEC Input Bias Current
VFB Input Voltage Range
VFB Input Bias Current
VFB Regulation Point
VFB to CCV Transconductance
VFB Zero-Voltage Crossing Threshold
CCV Output Impedance
DPWM Chopping Frequency
Lamp-Out Detection Timeout Timer
SDA, SCL, SUS Input Low Voltage
SDA, SCL, SUS Input High Voltage
SDA, SCL, SUS Input Hysteresis
SDA, SCL, SUS Input Bias Current
SDA Output Low Sink Current
SCL Serial Clock High Period
SCL Serial Clock Low Period
START Condition Setup Time
START Condition Hold Time
SDA Valid to SCL Rising-Edge Setup Time,
Slave Clocking-In Data
SCL Falling Edge to SDA Transition
SCL Falling Edge to SDA Valid,
Reading Out Data
V
SDA
= 0.4V
T
HIGH
T
LOW
t
SU:STA
t
HD:STA
t
SU:DAT
t
HD:DAT
T
DV
-1
4
4
4.7
4.7
4
250
0
700
2.1
300
+1
V
IFB
< 0.1V (Note 1)
204
1.14
1V < V
CCV
< 2.7V
-10
20
210
1.22
216
1.30
0.8
V
VFB
= 0.5V
V
ISEC
= 1.25V
-2
1.20
-2
-2
-0.5
490
510
40
+10
1.25
V
IFB
= 0.4V
LOT = REF
1V < V
CCI
< 2.5V
CONDITIONS
MIN
0.5
-2
-1.7
380
-2
500
600
100
20
+2
1.30
+2
+2
+0.5
530
400
TYP
MAX
V
REF
+2
+1.7
420
+2
700
UNITS
V
µA
V
mV
µA
mV
µS
MΩ
V
V
µA
V
µA
mV
µS
mV
MΩ
Hz
s
V
V
mV
µA
mA
µs
µs
µs
µs
ns
ns
ns
MAX8709B
_______________________________________________________________________________________
3
High-Efficiency CCFL Backlight
Controller with SMBus Interface
MAX8709B
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1. V
BATT
= 12V, V
LOT
= V
REF
, V
CC
= V
DD,
V
SUS
= 5.3V,
T
A
= -40°C to +85°C.
Typical values are at T
A
= +25°C,
unless otherwise noted.) (Note 2)
PARAMETER
V
BATT
Input Voltage Range
V
BATT
Quiescent Current
V
BATT
Quiescent Current, Shutdown
V
CC
Output Voltage, Normal Operation
V
CC
Output Voltage, Shutdown
V
CC
Undervoltage-Lockout Threshold
V
CC
Power-On Reset (POR) Threshold
REF Output Voltage, Normal Operation
GH1, GH2, GL1, GL2 On-Resistance
BST1, BST2 Leakage Current
Input Resonant Frequency
Minimum Off-Time
Maximum Off-Time
Current-Limit Threshold
LX1 - GND, LX2 - GND (Fixed)
Current-Limit Threshold
LX1 - GND, LX2 - GND (Adjustable)
Current-Limit Leading-Edge Blanking
LOT Input Voltage Range
LOT Input Bias Current
IFB Input Voltage Range
IFB Regulation Point
IFB Input Bias Current
IFB Lamp-Out Threshold
ISEC Input Voltage Range
ISEC Regulation Point
ISEC Input Bias Current
VFB Input Voltage Range
VFB Input Bias Current
VFB Regulation Point
VFB Zero-Voltage Crossing Threshold
DPWM Chopping Frequency
V
VFB
= 0.5V
V
ISEC
= 1.25V
V
IFB
= 0.4V
LOT = REF
ILIM = V
CC
V
ILIM
= 0.5V
V
ILIM
= 2.0V
CONDITIONS
V
CC
= V
DD
= V
BATT
V
CC
= V
DD
= open
V
SUS
= 5.5V
SUS = GND
V
SUS
= 5.5V, 6V < V
BATT
< 28V,
0 < I
LOAD
< 20mA
SUS = GND, no load
V
CC
rising (leaving lockout)
V
CC
falling (entering lockout)
Rising edge
4.5V < V
CC
< 5.5V, I
LOAD
= 40µA
I
TEST
= 100mA, V
CC
= V
DD
= 5.3V
V
BST
_ = 12V, V
LX
_ = 7V
Guaranteed by design
25
180
18
180
80
370
250
0.5
-2
-1.7
380
-2
500
-2
1.20
-2
-2
-0.5
490
-10
204
4.0
0.90
1.95
2.70
2.05
18
5
300
380
38
220
120
430
450
V
REF
+2
+1.7
420
+2
700
+2
1.30
+2
+2
+0.5
530
+10
216
5.0
3.5
V
BATT
= 28V
V
BATT
= V
CC
= 5V
MIN
4.6
5.5
TYP
MAX
5.5
28.0
3
3
20
5.5
5.5
4.5
UNITS
V
mA
µA
V
V
V
V
V
Ω
µA
kHz
ns
µs
mV
mV
ns
V
µA
V
mV
µA
mV
V
V
µA
V
µA
mV
mV
Hz
4
_______________________________________________________________________________________
High-Efficiency CCFL Backlight
Controller with SMBus Interface
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1. V
BATT
= 12V, V
LOT
= V
REF
, V
CC
= V
DD,
V
SUS
= 5.3V,
T
A
= -40°C to +85°C.
Typical values are at T
A
= +25°C,
unless otherwise noted.) (Note 2)
PARAMETER
Lamp-Out Detection Timeout Timer
SDA, SCL, SUS Input Low Voltage
SDA, SCL, SUS Input High Voltage
SDA, SCL, SUS Input Bias Current
SDA Output Low Sink Current
SCL Serial Clock High Period
SCL Serial Clock Low Period
START Condition Setup Time
START Condition Hold Time
SDA Valid to SCL Rising-Edge Setup Time,
Slave Clocking-In Data
SCL Falling Edge to SDA Transition
V
SDA
= 0.4V
T
HIGH
T
LOW
t
SU:STA
t
HD:STA
t
SU:DAT
t
HD:DAT
2.1
-1
4
4
4.7
4.7
4
250
0
+1
CONDITIONS
V
IFB
< 0.1V (Note 1)
MIN
1.14
TYP
MAX
1.30
0.8
UNITS
s
V
V
µA
mA
µs
µs
µs
µs
ns
ns
MAX8709B
Note 1:
Corresponds to 256 DPWM cycles.
Note 2:
Specifications to -40°C are guaranteed by design based on final characterization results.
Typical Operating Characteristics
(Circuit of Figure 1. V
BATT
= 12V, V
LOT
= V
REF
, V
CC
= V
DD,
V
SUS
= 5.3V, T
A
= +25°C, unless otherwise noted.)
LOW INPUT-VOLTAGE
OPERATION (V
BATT
= 8V)
MAX8709 toc01
HIGH INPUT-VOLTAGE
OPERATION (V
BATT
= 20V)
MAX8709 toc02
LINE-TRANSIENT RESPONSE
MAX8709 toc03
0V A
0V A
8V
A
0V B
0V B
0V B
C
0V
0V
C
0V C
D
0V
10μs/div
A: V
IFB
, 2V/div
B: V
VFB
, 2V/div
C: V
LX1
, 10V/div
D: V
LX2
, 10V/div
A: V
IFB
, 2V/div
B: V
VFB
, 2V/div
C: V
LX1
, 10V/div
D: V
LX2
, 10V/div
D
10μs/div
A: V
BATT
, 5V/div
B: V
IFB
, 2V/div
C: V
VFB
, 2V/div
D: V
LX1
, 10V/div
0V
40μs/div
0V
D
_______________________________________________________________________________________
5
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