General Description
The MAX8729 cold-cathode-fluorescent lamp (CCFL)
inverter controller is designed to drive multiple CCFLs
using the half-bridge inverter consisting of two external
n-channel power MOSFETs. The half-bridge topology
minimizes the component count, while providing near
sinusoidal drive waveforms. The MAX8729 operates in
resonant mode during striking and switches over to con-
stant-frequency operation after all the lamps are lit. This
unique feature ensures reliable striking under all condi-
tions and reduces the transformer stress.
The MAX8729 provides accurate lamp-current regulation
(±2.5%). The lamp current is adjustable with an external
resistor. The MAX8729 changes the brightness by turning
the CCFL on and off using a digital pulse-width modula-
tion (DPWM) method, while maintaining the lamp current
constant. The brightness can be adjusted with an analog
voltage on the CNTL pin, or with an external PWM signal.
The MAX8729 is capable of synchronizing and adjusting
the phase of the gate drivers and DPWM oscillator. These
features allow multiple MAX8729 ICs to be connected in a
daisy-chain configuration. The switching frequency and
DPWM frequency of the master IC can be easily adjusted
using external resistors, or synchronized with system sig-
nals. If the controller loses the external sync signals, it
switches over to the internal oscillators and keeps operat-
ing. Phase-shift select pins PS1 and PS2 can be used to
program four different phase shifts, allowing up to five
MAX8729s to be used together.
The MAX8729 protects the inverter from lamp-out, sec-
ondary overvoltage, and secondary short-circuit faults.
The MAX8729 can drive large-power MOSFETs typically
used in applications where one power stage drives four
or more CCFL tubes in parallel. An internal 5.35V linear
regulator powers the MOSFET drivers and most of the
internal circuitry. The MAX8729 is available in a low-cost,
28-pin QSOP package and operates over the -40°C to
+85°C extended temperature range.
Applications
LCD Monitors
LCD TVs
Notebook Computers
Automotive Infotainment
Features
Low-Cost, Half-Bridge Inverter Topology
Resonant Mode Striking Ensures Startup
Constant-Frequency Operation After Lamp
Ignition
Drives Large External MOSFETs
Supports Multilamp Applications
Sync and Phase-Shift Controls Allow Daisy-
Chained Operation
Adjustable Switching Frequency and DPWM
Frequency
±2.5% Lamp-Current Regulation
10:1 Dimming Range
Accurate Analog-Dimming Control
Lamp-Out Detection with Adjustable Timeout
Secondary Current and Voltage Limiting
Primary Current Limit with R
DS(ON)
Sensing
Adjustable DPWM Rise and Fall Time
Low-Cost, 28-Pin QSOP Package
M
Constant-Frequency, Half-Bridge CCFL
Inverter Controller
________________________________________________________________
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.
1
Ordering Information
MAX8729
LX
GL
GH
VFB
ISEC
IFB
COMP
PGND
GND
V
CC
BST
V
DD
IN
TFLT
PCOMP
LF
HF
SHDN
CNTL
SEL
DPWM
LFCK
HFCK
PSCK
PS1
PS2
VCC
VCC
INPUT
HSYNC
LSYNC
CCFL
ON/OFF
DIMMING
1
2
3
5
4
8
7
12
22
16
15
9
11
13
14
10
21
6
20
18
17
19
26
27
23
24
25
28
Simplified Operating Circuit
19-3754; Rev 0; 8/05
PART
TEMP RANGE
-40
°
C to +85
°
C
PIN-PACKAGE
28 QSOP
MAX8729EEI
Pin Configuration appears at end of data sheet.