Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - lighting/front end device controller CCFL controller WFQFN 28 Surface-mount

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 opera-

tion 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 dim-

ming 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 pow-

ers 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 tem-

perature range.

Applications

● Notebooks

● LCD Monitors

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 Lamp

Current 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

Pin Configuration appears at end of data sheet.

19-3874; Rev 3; 4/14

+Denotes a lead-free package.

*EP = Exposed paddle.

SMBus is a trademark of Intel Corp.

PART TEMP RANGE

PIN-

PACKAGE

PKG

CODE

MAX8759ETI+ -40°C to +85°C

28 Thin QFN-EP*

5mm x 5mm

T2855-6

CCFL

BATT

GND

DEL

SDA

SCL

PWMI

PWMO

FREQ

VALS

ALS

PGND1

BST2

BST1

GH1

LX1

LX2

GL1

PGND2

GL2

GH2

IFB1

IFB2

VFB

ISEC

COMP

TFLT

PWM INPUT

INPUT VOLTAGE

SMB_DATA

SMB_CLOCK

ALS SUPPLY

ALS OUTPUT

7.5V TO 24V

MAX8759

MAX8759 Low-Cost, SMBus, CCFL Backlight Controller

Minimal Operating Circuit

Ordering Information

Summary of content (31 pages)

PAGE 1
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller 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.
PAGE 2
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller 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 FREQ, VCC, VDD to GND........................................-0.3V to +6V SDA, SCL to GND....................................................-0.
PAGE 3
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Electrical Characteristics (continued) (Circuit of Figure 1, VBATT = 12V, VCC = VDD, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER IFB1, IFB2 Input Bias Current CONDITIONS 0 < VIFB1,2 < 3V -3 -3V < VIFB1,2 < 0 -230 IFB1, IFB2 Lamp-Out Threshold IFB1, IFB2 to COMP Transconductance MIN 0.
PAGE 4
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Electrical Characteristics (continued) (Circuit of Figure 1, VBATT = 12V, VCC = VDD, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER Zero-Crossing Delay Maximum Zero-Crossing Delay DEL Disable Threshold TFLT Charge Current TFLT Trip Threshold CONDITIONS MIN TYP MAX VBATT = 9V, RTHR = 120kW 0 0.15 0.30 VBATT = 12V, RTHR = 120kW 1.50 1.80 2.10 VBATT = 18V, RTHR = 120kW 3.2 3.8 4.4 DEL rising 4.
PAGE 5
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Electrical Characteristics (Circuit of Figure 1, VBATT = 12V, VCC = VDD, TA = -40°C to +85°C).(Note 1) PARAMETER BATT Input Voltage Range CONDITIONS MIN TYP MAX VCC = VDD = VBATT 4.5 5.5 VCC = VDD = open 5.5 28.0 VBATT = 28V 5 VBATT = VCC = 5V 5 UNITS V BATT Quiescent Current MAX8759 is enabled VCC Output Voltage, Normal Operation MAX8759 is enabled, 6V < VBATT < 28V, 0 < ILOAD < 10mA 5.2 5.
PAGE 6
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Electrical Characteristics (continued) (Circuit of Figure 1, VBATT = 12V, VCC = VDD, TA = -40°C to +85°C).(Note 1) PARAMETER CONDITIONS MIN PWMI Input Low Voltage PWMI Input High Voltage 5 MAX8759 is enabled TFLT Trip Threshold % 9.7 10.3 0 1.8 V 5.10 5.50 V 60 Ω VBATT = 9V, RTHR = 100kΩ 0 0.3 VBATT = 12V, RTHR = 100kΩ 1.50 2.10 VBATT = 16V, RTHR = 100kΩ 3.2 4.4 DEL rising DEL falling 4.5 3.9 µs µs V VISEC < 1.
PAGE 7
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Typical Operating Characteristics (Circuit of Figure 1, VIN = 12V, VCC = VDD, TA = +25°C, unless otherwise noted.) LOW-INPUT VOLTAGE OPERATION (VIN = 8.0V) HIGH-INPUT VOLTAGE OPERATION (VIN = 20.
PAGE 8
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = 12V, VCC = VDD, TA = +25°C, unless otherwise noted.) OPEN-LAMP VOLTAGE LIMITING AND TIMEOUT SECONDARY SHORT-CIRCUIT PROTECTION AND TIMEOUT MAX8759 toc011 A A B B C C C: TFLT, 5V/div DPWM FREQUENCY vs. RFREQ 250 200 150 100 100 150 200 250 300 ILAMP = 4mA 4 6.2 6.1 5.9 5.8 5.7 5 10 15 20 5.6 25 5 10 15 20 NORMALIZED BRIGHTNESS vs.
PAGE 9
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = 12V, VCC = VDD, TA = +25°C, unless otherwise noted.) NORMALIZED BRIGHTNESS vs. SMBus BRIGHTNESS AND PWMI DUTY CYCLE 60 40 20 0 0.8 VALS = 1.8V SMB = 0xFF 0.2 0.4 0.6 0.8 VALS = 1.8V 0.6 0.4 0.2 SMB = 0x80 0 MAX8759 toc20 80 1.0 MAX8759 toc19 NORMALIZED BRIGHTNESS (%) 100 NORMALIZED BRIGHTNESS vs. ALS VOLTAGE AND PWMI DUTY CYCLE 0 1.0 VALS = 0.8V 0 0.2 0.
PAGE 10
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Pin Description PIN NAME 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 openlamp and secondary overcurrent faults. 5 VALS Ambient-Light-Sensor Supply Pin.
PAGE 11
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Pin Description (continued) PIN NAME 18 BST1 19 PGND1 20 GL1 Low-Side MOSFET NL1 Gate Driver Output 21 VDD Low-Side Gate-Driver Supply Input. Connect VDD to the output of the internal linear regulator (VCC). Bypass VDD with a 0.1µF capacitor to PGND. 22 GL2 Low-Side MOSFET NL2 Gate-Driver Output 23 PGND2 24 BST2 GH2 Gate-Driver Supply Input. Connect a 0.1µF capacitor from LX2 to BST2.
PAGE 12
MAX8759 INPUT VOLTAGE 7.5V TO 24V Low-Cost, SMBus, CCFL Backlight Controller F1 2A 21 C7 0.1µF 27 11 VCC 28 C9 0.47µF SMB_DATA 3 PWM INPUT VDD BST2 DEL BST1 VCC GH1 7 8 SDA LX1 LX2 SCL GL1 PGND1 PWMO PGND2 GL2 FREQ R3 169kΩ 1% ALS SUPPLY GH2 IFB1 5 IFB2 VALS VFB C15 0.1µF ISEC ALS OUTPUT 6 C8 0.47µF 24 18 C2 2.2µF FDC6561AN 17 C10 0.1µF 16 26 N1A N1B N2A N2B 20 ALS COMP TFLT 19 C3 2.2µF C11 0.
PAGE 13
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Typical Operating Circuit The MAX8759 typical operating circuit (Figure 1) is a single-lamp CCFL backlight inverter for notebook computer TFT LCD panels. The input voltage range of the circuit is from 7.5V to 24V. The maximum RMS lamp current is set to 6mA and the maximum RMS striking voltage is set to 1800V. Table 1 lists some important components and Table 2 lists the component suppliers’ contact information.
PAGE 14
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller LINEAR REGULATOR BATT BIAS EN GND RDY UVLO COMPARATOR 4.3V VCC RDY VALS MAX8759 VCC OC COMP ISEC OC 1.21V S ZX Q R OPEN-LAMP COMP MIN TFLT 135µA FAULT LATCH 1µA FW MAX FW VREF COMP SHUTDOWN UV COMP ERROR AMP 1000µA BST1 100µA DH 2.
PAGE 15
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller PWMO BUFFER A PWMI D MUX "1" PWM_MD DIGITAL MULTIPLIER BUFFER MUX DPWM SETTING ALS A DIGITAL POT D PWM_SEL ALS CLAMP OFFSET MUX ALS_CTL FAULT/ STATUS REGISTER 0X02 SDA SCL ALS STATUS REGISTER 0X04 ALS LOW-LIMIT REGISTER 0X05 ALS HIGH-LIMIT REGISTER 0X06 SMBus INTERFACE BRIGHT CONTROL REGISTER 0X00 DEVICE CONTROL REGISTER INVERTER ON/OFF 0X01 SMBus AND AMBIENT-LIGHT-SENSOR INPUT BLOCK Figure 3.
PAGE 16
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller VBATT NH1 ON VBATT NH2 OFF T1 NH1 OFF NH2 ON T1 C2 C2 LX1 LX2 NL1 OFF LX1 NL2 ON LX2 NL1 ON NL2 OFF (a) (c) VBATT VBATT NH1 OFF NH2 OFF T1 NH1 OFF NH2 OFF T1 C2 C2 LX1 LX2 NL1 ON LX1 NL2 ON LX2 NL1 ON NL2 ON (BODY DIODE TURNS ON FIRST) (BODY DIODE TURNS ON FIRST) (b) (d) Figure 4.
PAGE 17
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller CS L 1:N 4 AC SOURCE CCFL VOLTAGE GAIN (V/V) CP (a) C C'S = S2 N L AC SOURCE CP 3 2 1 0 RL RL INCREASING 0 20 40 60 80 100 FREQUENCY (kHz) (b) Figure 5. Equivalent Resonant Tank Circuit Figure 6. Frequency Response of the Resonant Tank lamp current is sensed with a resistor connected in series with the low-voltage terminal of the lamp.
PAGE 18
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Dimming Control to 1.8V. The MAX8759 compares the ALS input voltage against user-programmable low and high limits. When the ALS input voltage is below the low limit, the brightness is clamped to the ALS low limit. When the ALS input voltage is above the high limit, the brightness is clamped to the ALS high limit. If the minimum ALS setting is below 10%, the brightness is clamped to 10%.
PAGE 19
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Fault Protections Secondary Voltage Limiting (VFB) Lamp-Out Protection For safety, the MAX8759 monitors the lamp-current feedback inputs (IFB1 and IFB2) to detect faulty or open CCFL tubes. As described in the Lamp-Current Regulation section, the voltage on IFB1 and IFB2 is internally full-wave rectified. If the rectified IFB1 or IFB2 voltage is below 600mV, the MAX8759 charges the TFLT capacitor with 1µA.
PAGE 20
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller WRITE-BYTE FORMAT S ADDRESS WR ACK COMMAND ACK DATA ACK P — 7 BITS 1b 1b 8 BITS 1b 8 BITS 1b — SLAVE ADDRESS COMMAND BYTE: SELECTS WHICH REGISTER YOU ARE WRITING TO READ-BYTE FORMAT DATA BYTE: DATA GOES INTO THE REGISTER SET BY THE COMMAND BYTE S ADDRESS WR ACK COMMAND ACK S ADDRESS RD ACK DATA /// P — 7 BITS 1b 1b 8 BITS 1b — 7 BITS 1b 1b 8 BITS 1b — SLAVE ADDRESS COMMAND BYTE: SELECTS WHICH REGISTER YOU A
PAGE 21
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller A tLOW B tHIGH C D E F G H I J K L M SMBCLK SMBDATA tSU:STA tHD:STA A = START CONDITION. B = MSB OF ADDRESS CLOCKED INTO SLAVE. C = LSB OF ADDRESS CLOCKED INTO SLAVE. D = R/W BIT CLOCKED INTO SLAVE. E = SLAVE PULLS SMBDATA LINE LOW . tSU:DAT tHD:DAT tHD:DAT F = ACKNOWLEDGE BIT CLOCKED INTO MASTER. G = MSB OF DATA CLOCKED INTO SLAVE. H = LSB OF DATA CLOCKED INTO SLAVE. I = SLAVE PULLS SMBDATA LINE LOW.
PAGE 22
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller A tLOW B C tHIGH D E F G H J I K SMBCLK SMBDATA tSU:STA tHD:STA tSU:DAT A = START CONDITION. B = MSB OF ADDRESS CLOCKED INTO SLAVE. C = LSB OF ADDRESS CLOCKED INTO SLAVE. D = R/W BIT CLOCKED INTO SLAVE. tHD:DAT tSU:DAT E = SLAVE PULLS SMBDATA LINE LOW. F = ACKNOWLEDGE BIT CLOCKED INTO MASTER. G = MSB OF DATA CLOCKED INTO MASTER. H = LSB OF DATA CLOCKED INTO MASTER. tSU:STO tBUF I = ACKNOWLEDGE CLOCK PULSE. J = STOP CONDITION.
PAGE 23
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Brightness Control Register [0x00] (POR = 0xFF) The brightness control register of the MAX8759 contains 8 bits and supports 256 brightness levels. A write-byte cycle to register 0x00 sets the brightness level if the inverter is in SMBus mode. A write-byte cycle to register 0x00 has no effect if the inverter is not in SMBus mode. A read-byte cycle to register 0x00 returns the current brightness level regardless of the operation mode.
PAGE 24
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller The relationships among these 3 control bits can be thought of as specifying an operating mode for the inverter. The defined modes are shown in Table 4. Note that depending on the settings of some bits, other bits have no effect and are don’t-care bits—they are shown with a value of X in Table 4. For example, when the ALS_CTL bit is 1, the value of PWM_SEL has no effect on the operation of the inverter, so its value is shown as X.
PAGE 25
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Identification Register [0x03] (POR = 0x01) The identification register contains two bit fields to denote the manufacturer and the silicon revision. The bit field widths allow up to 32 vendors with up to eight silicon revisions each. This register is read only. A write-byte cycle to register 0x03 has no effect. BIT 7 (R) BIT 6 (R) BIT 5 (R) BIT 4 (R) BIT 3 (R) BIT 2 (R) BIT 1 (R) BIT 0 (R) MFG4 MFG3 MFG2 MFG1 MFG0 REV2 REV1 REV0 MFG[4..
PAGE 26
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller ALS High-Limit Register [0x06] (POR = 0xFF) The value in this read-write register reflects the highest possible brightness value the inverter can set based on inputs from the ALS. Users can change this value so that they can control the effect of ALS. A write-byte cycle to register 0x06 sets the highest possible brightness value that can be set based on ALS inputs.
PAGE 27
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller to set the desired maximum RMS secondary voltage VLAMP(RMS)_MAX: = C5 2 × VLAMP(RMS)_MAX 2.3V × C4 where the 2.3V is the typical value of the VFB peak voltage when the lamp is open. To set the maximum RMS secondary voltage to 1800V when C4 is 10pF, use 10nF for C5.
PAGE 28
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller The transformer core saturation should also be considered when selecting the operating frequency. The primary winding should have enough turns to prevent transformer saturation under all operating conditions. Use the following expression to calculate the minimum number of turns N1 of the primary winding: N1 > D MAX × VIN(MAX) B S × S × f MIN where DMAX is the maximum duty cycle (approximately 0.
PAGE 29
MAX8759 INPUT VOLTAGE 7.5V TO 21V Low-Cost, SMBus, CCFL Backlight Controller F1 2A VCC 1 C7 0.1µF 27 11 28 VCC C9 0.47µF SMB_DATA 3 PWM INPUT VDD BST2 DEL BST1 VCC GH1 7 SDA LX1 LX2 SCL GL1 PWMO C12 1µF PGND2 GL2 GH2 9 FREQ R3 169kΩ 1% IFB1 IFB2 ISEC ALS SUPPLY 5 C8 1µF 24 18 17 16 26 C10 0.1µF N1A N1B C2 2.2µF 1 2 N2A C4 10pF 3kV D3 N2B 19 HV LV FDS6990A 22 C3 2.
PAGE 30
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller 6) Ensure the feedback connections are short and direct. To the extent possible, IFB1, IFB2, VFB, and ISEC connections should be far away from the high-voltage traces and the transformer. 8) The traces to the capacitive voltage-divider on the transformer’s secondary need to be widely separated to prevent arcing. Moving these traces to opposite sides of the board can be beneficial in some cases.
PAGE 31
MAX8759 Low-Cost, SMBus, CCFL Backlight Controller Revision History REVISION NUMBER REVISION DATE 3 4/14 DESCRIPTION Removed automotive reference in Applications section PAGES CHANGED 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com. Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product.