参数资料
| 型号： | MAX8722CEEG+ |
| 厂商： | Maxim Integrated |
| 文件页数： | 15/21页 |
| 文件大小： | 0K |
| 描述： | IC CCFL BACKLIGHT CTRL 24-QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| 类型： | CCFL 控制器 |
| 频率： | 30 ~ 80 kHz |
| 电流 - 电源： | 1mA |
| 电流 - 输出： | 300mA |
| 电源电压： | 4.6 V ~ 28 V |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 24-SSOP（0.154"，3.90mm 宽） |
| 供应商设备封装： | 24-QSOP |
| 包装： | 管件 |
Low-Cost CCFL Backlight Controller
Transformer Secondary Voltage Limiting
The MAX8722C reduces the voltage stress on the trans-
former’s secondary winding by limiting the secondary
voltage during startup and open-lamp faults. The AC
voltage across the transformer secondary winding is
sensed through a capacitive voltage-divider. The small
voltage across the larger capacitor of the divider is fed
to the VFB input and is internally half-wave rectified. An
overvoltage comparator compares the VFB voltage with
a 2.3V (typ) internal threshold. Once the sense voltage
exceeds the overvoltage threshold, the MAX8722C
turns on a 1100μA current source that discharges the
COMP capacitor. The high-side MOSFET on-time short-
ens as the COMP voltage decreases, reducing the
transformer secondary’s peak voltage below the thresh-
old set by the capacitive voltage-divider.
Lamp Startup
A CCFL is a gas discharge lamp that is normally driven
in the avalanche mode. To start ionization in a nonion-
ized lamp, the applied voltage (striking voltage) must
be increased to the level required for the start of
avalanche. At low temperatures, the striking voltage
can be several times the typical operating voltage.
Because of the MAX8722C’s resonant topology, the strik-
ing voltage is guaranteed. Before the lamp is ionized, the
lamp impedance is infinite. The transformer secondary
leakage inductance and the high-voltage parallel capaci-
tor determine the unloaded resonant frequency. Since
the unloaded resonant circuit has a high Q, it can gener-
ate very high voltages across the lamp.
Upon power-up, V COMP slowly rises, increasing the
duty cycle of the high-side MOSFET switches and pro-
viding a measure of soft-start.
Feed-Forward Control and
Dropout Operation
The MAX8722C is designed to maintain tight control of
the lamp current under all transient conditions. The
feed-forward control instantaneously adjusts the on-
Feed-forward control is implemented by increasing
the internal voltage ramp rate for higher V BATT . This
has the effect of varying t ON as a function of the in-
put voltage while maintaining approximately the same
signal levels at V COMP . Since the required voltage
change across the compensation capacitor is minimal,
the controller’s response to input voltage changes is
essentially instantaneous.
DPWM Dimming Control
The MAX8722C controls the brightness of the CCFL by
chopping the lamp current on and off using a low-fre-
quency (between 100Hz and 350Hz) DPWM signal
either from the internal oscillator or from an external sig-
nal source. The CCFL brightness is proportional to the
DPWM duty cycle, which can be adjusted from 9.766%
to 100% by the CNTL pin. CNTL is an analog input with
a usable input voltage range between 0 and 2000mV,
which is digitized to select one of 128 brightness levels.
As shown in Figure 6, the MAX8722C ignores the first
25 steps, so the first 25 steps all represent the same
brightness. When V CNTL is between 0 and 195.3mV,
the DPWM duty cycle is always 9.766%. When V CNTL is
above 195.3mV, a 7.8125mV change on CNTL results
in a 0.3906% change in the DPWM duty cycle. When
V CNTL is equal to or above 2000mV, the DPWM duty
cycle is always 100%.
100
90
80
60
70
50
40
30
20
time for changes in input voltage (V BATT ). This feature
provides immunity to input-voltage variations and sim-
plifies loop compensation over wide input voltage
ranges. The feed-forward control also improves the line
regulation for short on-times and makes startup tran-
10
0
0
400
800 1200 1600
CONTROL VOLTAGE (mV)
2000
sients less dependent on the input voltage.
Figure 6. Theoretical Brightness vs. Control Voltage
______________________________________________________________________________________
15
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8722CEEG+ | 功能描述:显示驱动器和控制器 CCFL Backlight Controller RoHS:否 制造商:Panasonic Electronic Components 工作电源电压:2.7 V to 5.5 V 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:QFN-44 封装:Reel |
| MAX8722CEEG+T | 功能描述:显示驱动器和控制器 CCFL Backlight Controller RoHS:否 制造商:Panasonic Electronic Components 工作电源电压:2.7 V to 5.5 V 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:QFN-44 封装:Reel |
| MAX8722EEG | 功能描述:显示驱动器和控制器 RoHS:否 制造商:Panasonic Electronic Components 工作电源电压:2.7 V to 5.5 V 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:QFN-44 封装:Reel |
| MAX8722EEG+ | 功能描述:显示驱动器和控制器 CCFL Backlight Controller RoHS:否 制造商:Panasonic Electronic Components 工作电源电压:2.7 V to 5.5 V 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:QFN-44 封装:Reel |
| MAX8722EEG+T | 功能描述:显示驱动器和控制器 CCFL Backlight Controller RoHS:否 制造商:Panasonic Electronic Components 工作电源电压:2.7 V to 5.5 V 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:QFN-44 封装:Reel |
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