MAX8751ETJ+ Maxim Integrated Products, MAX8751ETJ+ Datasheet

IC CNTRLR CCFL INV 32-TQFN

MAX8751ETJ+

Manufacturer Part Number
MAX8751ETJ+
Description
IC CNTRLR CCFL INV 32-TQFN
Manufacturer
Maxim Integrated Products
Type
CCFL Controllerr
Datasheet

Specifications of MAX8751ETJ+

Frequency
30 ~ 80 kHz
Current - Supply
3.2mA
Voltage - Supply
6 V ~ 28 V
Operating Temperature
-40°C ~ 85°C
Package / Case
32-TQFN Exposed Pad
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Current - Output
-
Lead Free Status / Rohs Status
 Details
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 synchro-
nized 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
features 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 con-
troller loses the external sync signals, it switches over to
the internal oscillators 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.
19-3784; Rev 0; 8/05
Pin Configuration appears at end of data sheet.
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.
MAX8751ETJ
LCD TVs
LCD Monitors
PART
________________________________________________________________ Maxim Integrated Products
Ordering Information
-40°C to +85°C
TEMP RANGE
General Description
Notebook Computers
Automotive Infotainment
Fixed-Frequency, Full-Bridge CCFL
Applications
PIN-PACKAGE
32 TQFN
♦ All n-Type MOSFET Low-Cost, Full-Bridge,
♦ Resonant-Mode Striking Ensures Startup
♦ Strong Gate Drivers Can Easily Drive Large
♦ Adjustable DPWM Frequency with Sync and
♦ 10:1 Dimming Range with Accurate Analog
♦ 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
7V TO 24V
GND
VIN
Fixed-Frequency Inverter Topology for Highest
Efficiency
External MOSFETs for Multilamp Applications
Phase-Shift Capability
Interface
BRIGHTNESS
V
CC
ON/OFF
3A
Inverter Controller
Minimal Operating Circuit
HFCK
IN
GND
V
SEL
SHDN
CNTL
PCOMP
HF
LF
HSYNC
LSYNC
LFCK
DPWM
PSCK
PS1
PS2
CC
MAX8751
PGND1
PGND2
COMP
BST1
BST2
ISEC
TFLT
GH1
GL1
GL2
GH2
VFB
LX1
LX2
IFB
Features
T1
CCFL
1

Related parts for MAX8751ETJ+

MAX8751ETJ+ Summary of contents

Page 1

... TEMP RANGE MAX8751ETJ -40°C to +85°C Pin Configuration appears at end of data sheet. ________________________________________________________________ Maxim Integrated Products 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. ♦ All n-Type MOSFET Low-Cost, Full-Bridge, Fixed-Frequency Inverter Topology for Highest Efficiency ♦ ...

Page 2

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. GND ..............................................................-0.3V to +6V CC GH1 to LX1 ................................................-0. ...

Page 3

Fixed-Frequency, Full-Bridge CCFL ELECTRICAL CHARACTERISTICS (continued 24V 0°C to +85°C, unless otherwise noted. Typical values are PARAMETER IFB Lamp-Out Threshold Reject 1µs glitches IFB-to-COMP Transconductance 1V < V COMP Output Impedance COMP ...

Page 4

Fixed-Frequency, Full-Bridge CCFL Inverter Controller ELECTRICAL CHARACTERISTICS (continued 24V 0°C to +85°C, unless otherwise noted. Typical values are PARAMETER LF Input Frequency Range Slave mode, V LSYNC Input Frequency Range R LF ...

Page 5

Fixed-Frequency, Full-Bridge CCFL ELECTRICAL CHARACTERISTICS (V = 24V -40°C to +85°C, unless otherwise noted.) (Note PARAMETER IN Input-Voltage Range IN Quiescent Current V SHDN IN Quiescent Current, Shutdown V SHDN V Output Voltage, Normal V ...

Page 6

Fixed-Frequency, Full-Bridge CCFL Inverter Controller ELECTRICAL CHARACTERISTICS (continued 24V -40°C to +85°C, unless otherwise noted.) (Note PARAMETER HF Input-Frequency Range Slave mode, V HSYNC Input Frequency Range Slave mode, V HFCK Input Frequency ...

Page 7

Fixed-Frequency, Full-Bridge CCFL (Circuit of Figure 12V +25°C, unless otherwise noted NORMAL OPERATION MAX8751 toc01 20µs/div A: VFB, 1V/div B: LX1, 10V/div C: LX2, 10V/div D: IFB, 2V/div 50% ...

Page 8

Fixed-Frequency, Full-Bridge CCFL Inverter Controller (Circuit of Figure 12V +25°C, unless otherwise noted DPWM SOFT-START MAX8751 toc07 100µs/div A: COMP, 1V/div B: IFB, 1V/div C: VFB, 1V/div SWITCHING FREQUENCY vs ...

Page 9

Fixed-Frequency, Full-Bridge CCFL (Circuit of Figure 12V +25°C, unless otherwise noted vs. TEMPERATURE CC 5. 12V IN NOT SWITCHING 5.38 5.36 5.34 5.32 5. TEMPERATURE ...

Page 10

Fixed-Frequency, Full-Bridge CCFL Inverter Controller PIN NAME Transformer Secondary Voltage-Feedback Input. VFB pin sets secondary overvoltage limit by using a capacitive voltage-divider between the high voltage of the CCFL lamp and GND. When the peak 1 VFB voltage on VFB ...

Page 11

Fixed-Frequency, Full-Bridge CCFL PIN NAME 18 GH2 Gate-Driver Output for High-Side MOSFET NH2 Gate-Driver Return for GH2. LX2 is the input to the primary current-limit and zero-crossing comparators. The controller senses the voltage across the low-side MOSFET NL2 (LX2 - ...

Page 12

Fixed-Frequency, Full-Bridge CCFL Inverter Controller 24V GND IN C10 1.0µF GND C12 SEL 1.0µF ON/OFF SHDN CNTL BRIGHTNESS PCOMP C7 0.1uF HF R3 100kΩ 150kΩ1% HFCK R5 HSYNC 1MΩ LSYNC ...

Page 13

Fixed-Frequency, Full-Bridge CCFL LINEAR IN REGULATOR GND V CC OVERVOLTAGE COMPARATOR 2.25V VFB OVER- CURRENT COMP 1200µA 100µA IFB F.W. RECT 790mV DPWM DIMMING CONTROL SEL LOGIC CNTL OPEN-LAMP COMPARATOR 780mV OVER- CURRENT ISEC 1.22V SECONDARY OVERCURRENT COMPARATOR TFLT Figure ...

Page 14

Fixed-Frequency, Full-Bridge CCFL Inverter Controller Detailed Description Figure 1 shows the Stand-Alone Typical Operating Circuit and Figure 2 shows the Functional Diagram of the MAX8751. The circuit in Figure 1 consists of a full- bridge inverter, which converts unregulated DC ...

Page 15

Fixed-Frequency, Full-Bridge CCFL PRIMARY CURRENT INTERNAL OSCILLATOR Figure 3. Fixed-Frequency Timing Diagram Figure 4. Resonant Operation Timing Diagram ______________________________________________________________________________________ DH1 DH2 DL1 DL2 PRIMARY CURRENT DH1 DH2 DL1 DL2 Inverter Controller 15 ...

Page 16

Fixed-Frequency, Full-Bridge CCFL Inverter Controller mode, at the beginning of the positive half cycle, NH1 and NL2 turn on and the primary current starts ramping up. The controller turns off NH1 as the primary current reaches its peak value. The ...

Page 17

Fixed-Frequency, Full-Bridge CCFL the end of the DPWM on-cycle, the dimming control logic turns on a 100µA internal current source, thus dis- charging the COMP capacitor linearly, gradually decreasing t and bringing lamp current to zero, thus ON providing soft-start. ...

Page 18

Fixed-Frequency, Full-Bridge CCFL Inverter Controller Secondary Current Limit (ISEC) The secondary current limit provides fail-safe protection in case of short circuit or leakage from the high-voltage terminal to ground. ISEC monitors the voltage across a sense resistor placed between the ...

Page 19

Fixed-Frequency, Full-Bridge CCFL Table 1. Phase-Shift Setting PIN SETTING PS2 PS1 MASTER X X GND GND GND GND Don’t care. Linear Regulator Output (V The internal linear regulator steps down ...

Page 20

Fixed-Frequency, Full-Bridge CCFL Inverter Controller Table 2. Operation Summary MASTER MODE USING PIN INTERNAL OSCILLATORS An analog voltage on CNTL CNTL sets the brightness. SEL Connect SEL to GND. Connect a resistor to GND to HF set the switching frequency. ...

Page 21

Fixed-Frequency, Full-Bridge CCFL 380mV = I LIM_MIN R DS(ON)_MAX 420mV = I LIM_MAX R DS(ON)_MIN MOSFETs must be able to dissipate the conduction losses plus the switching losses at both Calculate both terms. Ideally, the losses at ...

Page 22

Fixed-Frequency, Full-Bridge CCFL Inverter Controller Setting the Secondary Current Limit The MAX8751 limits the secondary current even if the IFB sense resistor is shorted or transformer secondary current finds its way to ground without passing through R1. ISEC monitors the ...

Page 23

Fixed-Frequency, Full-Bridge CCFL C S 1:N AC SOURCE (a) 2 Cs' = Cs'/ SOURCE (b) Figure 7. Simplified CCFL Inverte r Circuit 2 N ≤ 4π MIN where f is the minimum ...

Page 24

Fixed-Frequency, Full-Bridge CCFL Inverter Controller 30µA, the rise time is about three times longer than the fall time. Setting the Fault Delay Time The TFLT capacitor determines the delay time for both the open-lamp fault and secondary short-circuit fault. The ...

Page 25

Fixed-Frequency, Full-Bridge CCFL Pin Configuration TOP VIEW GL1 25 PGND1 26 27 GND 28 PCOMP MAX8751ETJ 29 COMP IFB 30 31 PS2 32 ISEC TQFN 5mm x 5mm ...

Page 26

Fixed-Frequency, Full-Bridge CCFL Inverter Controller (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information www.maxim-ic.com/packages.) 26 ______________________________________________________________________________________ Package Information ...

Page 27

... Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 27 © 2005 Maxim Integrated Products ...

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