Rainbow Electronics MAX8759 User Manual
General Description
The MAX8759 integrated cold-cathode fluorescent lamp
(CCFL) inverter controller is designed to drive CCFLs
using a full-bridge resonant inverter. The resonant operation ensures reliable striking and provides near-sinusoidal
waveforms over the entire input range. The controller
operates over a wide input-voltage range of 4.5V to 28V
with high power to light efficiency. The device also
includes safety features that effectively protect against
single-point fault conditions such as lamp-out, secondary
overvoltage, and secondary short-circuit faults.
The MAX8759 provides accurate lamp-current regulation (±2.5%) for superior CCFL inverter performance.
The lamp current is adjustable with an external resistor;
10:1 dimming range can be achieved by turning the
CCFL on and off using a digital pulse-width modulation
(DPWM) method, while maintaining the lamp-current
constant. The MAX8759 provides three mechanisms for
controlling brightness: 2-wire SMBus™-compatible
interface, external ambient-light sensor (ALS), or system PWM control. The MAX8759 supports Intel display
power-saving technology (DPST) to maximize battery
life. The device includes two lamp-current feedback
input pins that support dual-lamp applications with a
minimum number of external components.
The MAX8759 controls a full-bridge inverter for maximum efficiency and directly drives four external n-channel power MOSFETs. An internal 5.35V linear regulator
powers the MOSFET drivers and most of the internal
circuitry. The MAX8759 is available in a space-saving,
28-pin, thin QFN package and operates over a -40°C to
+85°C temperature range.
Applications
Notebooks
LCD Monitors
Automotive Infotainment
Features
♦ Accurate Dimming Control Using SMBus, PWM
Interface, or Ambient Light Sensor
♦ 10:1 Dimming Range with 256-Step Resolution
♦ Resonant-Mode Operation
Longer Lamp Life with Near Sinusoidal LampCurrent Waveform
Guaranteed Striking Capability
High-Power-to-Light Efficiency
♦ Wide Input-Voltage Range (4.5V to 28V)
♦ Input Feed-Forward for Excellent Line Rejection
♦ ±2.5% Lamp-Current Regulation
♦ Adjustable 1.5% Accurate DPWM Frequency
♦ Dual Lamp-Current Feedback Inputs
♦ Comprehensive Fault Protection
Secondary Voltage Limiting
Primary Current Limit with Lossless Sensing
Lamp-Out Protection with Adjustable Timeout
Secondary Short-Circuit Protection
♦ Small 28-Pin, 5mm x 5mm, Thin QFN Package
MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
MAX8759
Minimal Operating Circuit
19-3874; Rev 0; 10/05
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.
PART
TEMP RANGE
PINPACKAGE
PKG
CODE
MAX8759ETI+
5mm × 5mm
T2855-6
+ Denotes lead-free package.
*EP = Exposed pad.
Pin Configuration appears at end of data sheet.
SMBus is a trademark of Intel Corp.
-40°C to +85°C
28 Thin QFN-EP*
MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V
BATT
= 12V, VCC= V
DD,TA
= 0°C to +85°C. Typical values are at TA= +25°C, 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.
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
FREQ, V
CC
, VDDto GND .........................................-0.3V to +6V
SDA, SCL to GND.....................................................-0.3V to +6V
ALS, COMP, PWMI, PWMO,
TFLT, DEL, VALS 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)
IFB1, IFB2, ISEC, VFB to GND ....................................-3V to +6V
PGND1, PGND2 to GND .......................................-0.3V to +0.3V
Continuous Power Dissipation (TA= +70°C)
28-Pin Thin QFN 5mm x 5mm
(derate 21.3mW/°C above +70°C).............................1702mW
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
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
VCC = VDD = V
BATT
4.5 5.5
BATT Input Voltage Range
V
CC
= VDD = open 5.5
V
V
BATT
= 28V 2.5 5
BATT Quiescent Current
V
BATT
= VCC = 5V 5
mA
BATT Quiescent Current, Shutdown MAX8759 is disabled 0.1 2 µA
VCC Output Voltage, Normal Operation
MAX8759 is enabled, 6V < V
BATT
< 28V,
0 < I
LOAD
< 10mA
5.2
5.5 V
VCC Output Voltage, Shutdown MAX8759 is disabled, no load 3.5 4.3 5.5 V
VCC rising (leaving lockout) 4.3
VCC Undervoltage Lockout Threshold
V
CC
falling (entering lockout) 3.7
V
VCC Undervoltage Lockout Hysteresis 230 mV
VCC POR Threshold Rising edge
V
VCC POR Hysteresis 50 mV
GH1, GH2, GL1, GL2 On-Resistance,
Low State
I
TEST
= 100mA, VCC = VDD = 5V 3 6 Ω
GH1, GH2, GL1, GL2 On-Resistance,
High State
I
TEST
= 100mA, VCC = VDD = 5V 10 18 Ω
BST1, BST2 Leakage Current V
BST
_ = 12V, V
LX
_ = 7V 4 10 µA
Resonant Frequency Range Guaranteed by design 30 80 kHz
Minimum On-Time 350 500 700 ns
Maximum Off-Time 40 60 80 µs
Current-Limit Threshold LX1 - PGND1, LX2 - PGND2 415 430 445 mV
Zero-Current-Crossing Threshold LX1 - PGND1, LX2 - PGND2 3 8 13 mV
Current-Limit Leading-Edge Blanking 350 ns
IFB1, IFB2 Input-Voltage Range -3 +3 V
IFB1 Regulation Point 765 785 805 mV
IFB2 Regulation Point 780 800 820 mV
MAX8759 is enabled
28.0
5.35
1.75
MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
BATT
= 12V, VCC= V
DD,TA
= 0°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
0 < V
IFB1,2
< 3V -3 +3
IFB1, IFB2 Input Bias Current
-3V < V
IFB1,2
< 0
µA
IFB1, IFB2 Lamp-Out Threshold 575 600 625 mV
IFB1, IFB2 to COMP Transconductance 0.5V < V
COMP
< 4V 60 100 160 µS
COMP Output Impedance 61224MΩ
COMP Discharge Current During Overvoltage
or Overcurrent Fault
V
VFB
= 2.6V or V
ISEC
= 1.5V 500
µA
COMP Discharge Current During DPWM
Off-Time
V
COMP
= 1.5V 90 110 130 µA
DPWM Rising-to-Falling Ratio V
IFB1,2
= 0 2.5
ISEC Input Voltage Range -3 +3 V
ISEC Overcurrent Threshold
V
ISEC Input Bias Current V
ISEC
= 1.25V
µA
VFB Input Voltage Range -4 +4 V
VFB Input Impedance 150 300 450 MΩ
VFB Overvoltage Threshold 2.1 2.3 2.5 V
VFB Undervoltage Threshold 210 240 280 mV
VFB Undervoltage Delay R
FREQ
= 169kΩ 250 µs
R
FREQ
= 169kΩ, TA = +25°C to +85°C
213
R
FREQ
= 169kΩ
215
R
FREQ
= 340kΩ 106
DPWM Oscillator Frequency
R
FREQ
= 100kΩ 343
Hz
PWMO Output Impedance 20 40 60 kΩ
PWMI Input Low Voltage 0.7 V
PWMI Input High Voltage 2.1 V
PWMI Input Hysteresis 300 mV
PWMI Input Bias Current
µA
PWMI Input Frequency Range 5 50 kHz
PWMI Full-Range Accuracy 5 LSB
PWMI duty cycle = 100% 98 100
PWMI duty cycle = 50% 48 50 52PWMI Brightness Setting
PWMI duty cycle = 0% 9.7
%
ALS Full-Adjustment Range 0 1.8 V
ALS Full-Range Accuracy 5 LSB
ALS Input Bias Current
µA
VALS Output Voltage
MAX8759 is enabled, 6V < V
BATT
< 28V,
I
LOAD
= 1mA
V
VALS Leakage Current MAX8759 is disabled, VALS = GND -3 +3 µA
VALS On-Resistance MAX8759 is enabled 30 60 Ω
-230
1000 2000
1.18 1.21 1.26
-0.3 +0.3
207 210
205 210
-0.3 +0.3
-0.1 +0.1
5.10 5.30 5.50
10.0 10.3
MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
BATT
= 12V, VCC= V
DD,TA
= 0°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.)
PARAMETER CONDITIONS
UNITS
V
BATT
= 9V, R
THR
= 100kΩ 0
Zero-Crossing Delay
V
BATT
= 12V, R
THR
= 100kΩ
µs
Maximum Zero-Crossing Delay V
BATT
= 16V, R
THR
= 100kΩ 3.2 3.8 4.4 µs
DEL rising 4.5
DEL Disable Threshold
DEL falling 3.8
V
0.9 1.0 1.1
TFLT Charge Current
115 135 155
µA
TFLT Trip Threshold Rising edge 3.7 4 4.3 V
SDA, SCL, Input Low Voltage 0.7 V
SDA, SCL, Input High Voltage 2.1 V
SDA, SCL, Input Hysteresis 100 mV
SDA, SCL, Input Bias Current -1 +1 µA
SDA Output Low Sink Current V
SDA
= 0.4V 4 mA
SMBus Frequency 10 100 kHz
SMBus Free Time t
BUF
4.7 1 µs
SCL Serial Clock High Period t
HIGH
4µs
SCL Serial Clock Low Period t
LOW
4.7 µs
START Condition Setup Time t
SU:STA
4.7 µs
START Condition Hold Time t
HD:STA
4µs
STOP Condition Setup Time from SCL t
SU:STO
4µs
SDA Valid to SCL Rising-Edge Setup Time,
Slave Clocking in Data
t
SU:DAT
250 ns
SCL Falling Edge to SDA Transition t
HD:DAT
0ns
SCL Falling Edge to SDA Valid, Reading Out
Data
t
DV
200 ns
MIN TYP MAX
1.50 1.80 2.10
0.15 0.30
V
< 1.25V and V
ISEC
V
< 1.25V and V
ISEC
V
> 1.25V and V
ISEC
< 540mV; V
IFB
> 660mV; V
IFB
> 660mV; V
IFB
= 2V
FLT
= 2V -1.5 -1.2 -0.8
FLT
= 2V
FLT
MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V
BATT
= 12V, VCC= V
DD,TA
= -40°C to +85°C.) (Note 1)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
VCC = VDD = V
BATT
4.5 5.5
BATT Input Voltage Range
V
CC
= VDD = open 5.5
V
V
BATT
= 28V 5
BATT Quiescent Current
V
BATT
= VCC = 5V 5
mA
VCC Output Voltage, Normal Operation
MAX8759 is enabled, 6V < V
BATT
< 28V,
0 < I
LOAD
< 10mA
5.2 5.5 V
VCC Output Voltage, Shutdown MAX8759 is disabled, no load 3.5 5.5 V
VCC rising (leaving lockout) 4.3
VCC Undervoltage Lockout Threshold
V
CC
falling (entering lockout) 3.7
V
GH1, GH2, GL1, GL2 On-Resistance,
Low State
I
TEST
= 100mA, VCC = VDD = 5V 6 Ω
GH1, GH2, GL1, GL2 On-Resistance,
High State
I
TEST
= 100mA, VCC = VDD = 5V 18 Ω
Resonant Frequency Range Guaranteed by design 30 80 kHz
Minimum On-Time 350 700 ns
Maximum Off-Time 40 80 µs
Current-Limit Threshold LX1 - PGND1, LX2 - PGND2 410 450 mV
Zero-Current Crossing Threshold LX1 - PGND1, LX2 - PGND2 3 13 mV
IFB1, IFB2 Input Voltage Range -3 +3 V
IFB1 Regulation Point 760 810 mV
IFB2 Regulation Point 775 825 mV
IFB1, IFB2 Input Bias Current -3V < V
IFB1,2
< 0
µA
IFB1, IFB2 Lamp-Out Threshold 565 635 mV
IFB1, IFB2 to COMP Transconductance 0.5V < V
COMP
< 4V 60 160 µS
COMP Output Impedance 625MΩ
COMP Discharge Current During Overvoltage
or Overcurrent Fault
V
VFB
= 2.6V or V
ISEC
= 1.5V 500
µA
COMP Discharge Current During DPWM
Off-Time
V
COMP
= 1.5V 90 130 µA
ISEC Input Voltage Range -3 +3 V
ISEC Overcurrent Threshold
V
VFB Input Voltage Range -4 +4 V
VFB Input Impedance 150 450 MΩ
VFB Overvoltage Threshold 2.1 2.5 V
VFB Undervoltage Threshold 210 280 mV
DPWM Oscillator Frequency R
FREQ
= 169kΩ 203 217 Hz
PWMO Output Impedance 20 60 kΩ
MAX8759 is enabled
-230
1.18 1.26
28.0
2000
MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
6 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
BATT
= 12V, VCC= V
DD,TA
= -40°C to +85°C.) (Note 1)
PARAMETER CONDITIONS
UNITS
PWMI Input Low Voltage 0.7 V
PWMI Input High Voltage 2.1 V
PWMI Input Frequency Range 5 50 kHz
PWMI duty cycle = 100% 98
PWMI duty cycle = 50% 48 52PWMI Brightness Setting
PWMI duty cycle = 0% 9.7
%
ALS Full-Adjustment Range 0 1.8 V
VALS Output Voltage
MAX8759 is enabled, 6V < V
BATT
< 28V,
I
LOAD
= 1mA
V
VALS On-Resistance MAX8759 is enabled 60 Ω
V
BATT
= 9V, R
THR
= 100kΩ 0 0.3
Zero-Crossing Delay
V
BATT
= 12V, R
THR
= 100kΩ
µs
Maximum Zero-Crossing Delay V
BATT
= 16V, R
THR
= 100kΩ 3.2 4.4 µs
DEL rising 4.5
DEL Disable Threshold
DEL falling 3.9
V
0.8 1.2
TFLT Charge Current
115 155
µA
TFLT Trip Threshold Rising edge 3.7 4.3 V
SDA, SCL, Input Low Voltage 0.7 V
SDA, SCL, Input High Voltage 2.1 V
SDA Output Low-Sink Current V
SDA
= 0.4V 4 mA
SMBus Frequency 10 100 kHz
SMBus Free Time t
BUF
4.7 µs
SCL Serial Clock High Period t
HIGH
4µs
SCL Serial Clock Low Period t
LOW
4.7 µs
START Condition Setup Time t
SU:STA
4.7 µs
START Condition Hold Time t
HD:STA
4µs
STOP Condition Setup Time from SCL t
SU:STO
4µs
SDA Valid to SCL Rising-Edge Setup Time,
Slave Clocking in Data
t
SU:DAT
250 ns
SCL Falling Edge to SDA Transition t
HD:DAT
0ns
SCL Falling Edge to SDA Valid,
Reading Out Data
t
DV
200 ns
Note 1: Specifications to -40°C are guaranteed by design, not production tested.
MIN TYP MAX
5.10 5.50
V
< 1.25V and V
ISEC
V
< 1.25V and V
ISEC
V
> 1.25V and V
ISEC
< 540mV; V
IFB
> 660mV; V
IFB
> 660mV; V
IFB
= 2V
FLT
= 2V -1.5 -0.8
FLT
= 2V
FLT
1.50 2.10
10.3
MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
_______________________________________________________________________________________ 7
C
D
B
A
A: VFB, 2V/div
B: LX1, 10V/div
LOW-INPUT VOLTAGE OPERATION
(V
IN
= 8.0V)
MAX8759 toc01
10µs/div
C: LX2, 10V/div
D:IFB, 2V/div
C
D
B
A
A: VFB, 2V/div
B: LX1, 20V/div
HIGH-INPUT VOLTAGE OPERATION
(V
IN
= 20.0V)
MAX8759 toc02
10µs/div
C: LX2, 20V/div
D: IFB, 2V/div
C
D
B
A
A: V
IN
, 10V/div
B: COMP, 2V/div
LINE TRANSIENT RESPONSE
(8V TO 20V)
MAX8759 toc03
100µs/div
C: IFB, 2V/div
D: LX1, 20V/div
C
D
B
A
A: V
IN
, 10V/div
B: COMP, 2V/div
LINE TRANSIENT RESPONSE
(20V TO 8V)
MAX8759 toc04
100µs/div
C: IFB, 2V/div
D: LX1, 20V/div
C
B
A
A: VFB, 2V/div
B: COMP, 1V/div
MINIMUM BRIGHTNESS STARTUP WAVEFORM
(SMBus MODE, BRIGHTNESS REGISTER = 0x00)
MAX8759 toc05
2ms/div
C: IFB, 2V/div
C
B
A
A: VFB, 2V/div
B: COMP, 1V/div
MINIMUM BRIGHTNESS DPWM OPERATION
(SMBus MODE, BRIGHTNESS REGISTER = 0x00)
MAX8759 toc06
2ms/div
C: IFB, 2V/div
C
B
A
A: VFB, 2V/div
B: COMP, 1V/div
50% BRIGHTNESS DPWM OPERATION
(SMBus MODE, BRIGHTNESS REGISTER = 0x80)
MAX8759 toc07
2ms/div
C: IFB, 2V/div
C
B
A
A: VFB, 2V/div
B: COMP, 1V/div
DPWM SOFT-START
MAX8759 toc08
40µs/div
C: IFB, 2V/div
C
B
A
A: VFB, 2V/div
B: COMP, 1V/div
DPWM SOFT-STOP
MAX8759 toc09
40µs/div
C: IFB, 2V/div
Typical Operating Characteristics
(Circuit of Figure 1, VIN= 12V, VCC= VDD, TA= +25°C, unless otherwise noted.)
MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
8 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN= 12V, VCC= VDD, TA= +25°C, unless otherwise noted.)
C
B
A
A: VFB, 2V/div
B: COMP, 500mV/div
OPEN-LAMP VOLTAGE
LIMITING AND TIMEOUT
MAX8759 toc010
200ms/div
C: TFLT, 5V/div
C
B
A
A: ISEC, 2V/div
B: COMP, 1V/div
SECONDARY SHORT-CIRCUIT PROTECTION
AND TIMEOUT
MAX8759 toc011
2ms/div
C: TFLT, 1V/div
30
40
60
50
70
80
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX8759 toc12
VIN (V)
SWITCHING FREQUENCY (kHz)
51510 20 25
50
150
100
250
200
300
350
DPWM FREQUENCY
vs. R
FREQ
MAX8759 toc13
R
FREQ
(kΩ)
DPWM FREQUENCY (Hz)
50 150 200100 250 300 350
3
4
6
5
7
8
RMS LAMP CURRENT
vs. INPUT VOLTAGE
MAX8759 toc14
INPUT VOLTAGE (V)
RMS LAMP CURRENT (mA)
51510 20 25
I
LAMP
= 7mA
I
LAMP
= 6mA
I
LAMP
= 5mA
I
LAMP
= 4mA
5.6
5.8
5.7
6.0
5.9
6.1
6.2
51510 20 25
RMS LAMP CURRENT (I
LAMP
= 6mA)
vs. INPUT VOLTAGE
MAX8759 toc15
INPUT VOLTAGE (V)
RMS LAMP CURRENT (mA)
0
20
60
40
80
100
00.40.2 0.6 0.8 1.0
NORMALIZED BRIGHTNESS
vs. PWMI DUTY CYCLE
MAX8759 toc17
PWMI DUTY RATIO
NORMALIZED BRIGHTNESS (%)
0
20
60
40
80
100
0 0.80.4 1.2 1.6 2.0
NORMALIZED BRIGHTNESS
vs. ALS VOLTAGE
MAX8759 toc18
V
ALS
(V)
NORMALIZED BRIGHTNESS (%)
0
20
60
40
80
100
04020 60 80 100
NORMALIZED BRIGHTNESS
vs. SMBus BRIGHTNESS SETTING
MAX8759 toc16
BRIGHTNESS SETTING (%)
NORMALIZED BRIGHTNESS (%)
MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
_______________________________________________________________________________________ 9
0
20
60
40
80
100
00.40.2 0.6 0.8 1.0
NORMALIZED BRIGHTNESS
vs. SMBus BRIGHTNESS AND PWMI DUTY CYCLE
MAX8759 toc19
PWMI DUTY RATIO
NORMALIZED BRIGHTNESS (%)
SMB = 0xFF
SMB = 0x80
0
0.2
0.6
0.4
0.8
1.0
00.40.2 0.6 0.8 1.0
NORMALIZED BRIGHTNESS
vs. ALS VOLTAGE AND PWMI DUTY CYCLE
MAX8759 toc20
PWMI DUTY RATIO
V
ALS
= 1.8V
V
ALS
= 1.8V
V
ALS
= 0.8V
B
A
ALS TRANSIENT RESPONSE
(ALSDEL1 = ALSDEL0 = 0)
MAX8759 toc21
A: ALS, 1V/div B: COMP, 1V/div
1s/div
5.30
5.31
5.33
5.32
5.34
5.35
VCC LINE REGULATION
MAX8759 toc22
INPUT VOLTAGE (V)
V
CC
VOLTAGE (V)
81612 20 24
5.30
5.31
5.33
5.32
5.34
5.35
042681012
VCC LOAD REGULATION
MAX8759 toc23
LOAD CURRENT (mA)
V
CC
VOLTAGE (V)
VIN = 24V
VIN = 12V
5.27
5.28
5.30
5.29
5.31
5.32
-40 0-20 20 406080
VCC VOLTAGE
vs. TEMPERATURE
MAX8759 toc24
TEMPERATURE (°C)
V
CC
VOLTAGE (V)
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN= 12V, VCC= VDD, TA= +25°C, unless otherwise noted.)
MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
10 ______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1 BATT
Supply Input. BATT is the input to the internal 5.35V linear regulator that powers the device. Bypass BATT
to GND with a 0.1µF ceramic capacitor.
2 SDA SMBus Serial Data Input
3 SCL SMBus Serial Clock Input
4 TFLT
Fault-Timer Adjustment Pin. Connect a capacitor from TFLT to GND to set the time-out periods for open-
lamp and secondary overcurrent faults.
5 VALS Ambient-Light-Sensor Supply Pin. Bypass VALS to GND with a 0.1µF capacitor.
6 ALS Ambient-Light-Sensor Input
7 PWMI DPST Control Input
8
DPST Buffer Output. Connect a capacitor between PWMO and GND. The capacitor forms a lowpass filter
with an internal 40kΩ (typ) resistor for filtering the DPST signal.
9 FREQ
Chopping-Frequency Adjustment Pin. Connect a resistor from FREQ to GND to set the DPWM frequency:
f
DPWM
= 210Hz × 169kΩ / R
FREQ
.
10 COMP
Transconductance Error Amplifier Output. A compensation capacitor connected between COMP and GND
sets the rise and fall time of the lamp-current envelope in DPWM operation.
11 DEL
Adaptive Zero-Crossing-Delay Adjustment Pin. Connect a resistor between DEL and GND to adjust the
range of the zero-crossing delay. Connecting DEL to V
CC
disables the zero-crossing delay function.
12 IFB1
Lamp-Current-Feedback Input. The IFB1 sense signal is internally full-wave rectified. IFB1 is compared
with IFB2 and the larger is used for lamp-current regulation. The average value of the rectified signal is
regulated to 785mV (typ) by controlling the on-time of high-side switch. An open-lamp fault is generated if
the peak voltage of IFB1 is below 600mV for a fault delay period set by TFLT.
13 IFB2
Lamp-Current-Feedback Input. The IFB2 sense signal is internally full-wave rectified. IFB1 is compared
with IFB2 and the larger is used for lamp-current regulation. The average value of the rectified signal is
regulated to 800mV (typ) by controlling the on-time of high-side switch. An open-lamp fault is generated if
the peak voltage of IFB2 is below 600mV for a fault-delay period set by TFLT. IFB2 input can be disabled
by connecting IFB2 to V
CC
.
14 VFB
Transformer Secondary Voltage-Feedback Input. A capacitive voltage-divider between the high-voltage
terminal of the CCFL tube and GND sets the maximum average lamp voltage during striking and lamp-out
fault. When the peak voltage on VFB exceeds the internal overvoltage threshold, the controller turns on an
internal current sink, discharging the COMP capacitor to limit the switch on-time. The VFB pin is also used
to detect a secondary undervoltage condition. If the peak voltage on VFB is below 230mV continuously for
250µs during the DPWM ON period, the MAX8759 shuts down.
15 ISEC
Transformer Secondary Current-Feedback Input. A current-sense resistor connected between the low-
voltage end of the transformer secondary and the ground sets the maximum secondary current during
short-circuit fault. When the peak voltage on ISEC exceeds the internal overcurrent threshold, the
controller turns on an internal current sink discharging the COMP capacitor.
16 LX1
GH1 Gate-Driver Return. LX1 is the input to the current-limit and zero-crossing comparators. The device
senses the voltage across the low-side MOSFET NL1 to detect primary current zero crossing and primary
overcurrent.
17 GH1 High-Side MOSFET NH1 Gate Driver Output
PWMO
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