MAX8729 Datasheet, PDF (1/26 Pages) Maxim Integrated Products – Constant-Frequency, Half-Bridge CCFL Inverter Controller

19-3754; Rev 0; 8/05
Constant-Frequency, Half-Bridge CCFL
Inverter Controller
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
Notebook Computers
LCD TVs
Automotive Infotainment
Ordering Information
PART
MAX8729EEI
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
28 QSOP
Pin Configuration appears at end of data sheet.
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
Simplified Operating Circuit
INPUT
VCC
ON/OFF
DIMMING
3 _IN
5 _GND
4 _VCC
8 _SHDN
7 _CNTL
2 _SEL
12 _PSCK
22 _PS1
16 _PS2
15 _HF
VCC
VDD ²⁸
BST ²⁵
GH ²⁴
LX ²³
GL ²⁷
PGND ²⁶
VFB ¹⁹
ISEC ²⁰
IFB ¹⁸
COMP ¹⁷
CCFL
MAX8729
9 _LF
TFLT ⁶
11 DPWM
13 _HFCK
10 _LFCK
PCOMP ¹
HSYNC ¹⁴
LSYNC ²¹
________________________________________________________________ Maxim Integrated Products 1
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