参数资料
| 型号： | MAX8722CEEG+ |
| 厂商： | Maxim Integrated |
| 文件页数： | 17/21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
During the delay period, the current control loop tries to
maintain lamp-current regulation by increasing the
high-side MOSFET on-time. Because the open-circuit
lamp impedance is very high, the transformer sec-
ondary voltage rises as a result of the high Q-factor of
the resonant tank. Once the secondary voltage
exceeds the overvoltage threshold, the MAX8722C
turns on a 1100μA current source that discharges the
COMP capacitor. The on-time of the high-side MOSFET
is reduced, lowering the secondary voltage, as the
COMP voltage decreases. Therefore, the peak voltage
of the transformer secondary winding never exceeds
the limit set by a capacitive voltage-divider during the
lamp-out delay period.
Primary Overcurrent Protection (ILIM)
The MAX8722C senses transformer primary current in
each switching cycle. When the regulator turns on the
low-side MOSFET, a comparator monitors the voltage
drop from LX_ to GND. If the voltage exceeds the cur-
rent-limit threshold, the regulator turns off the high-side
switch at the opposite side of the primary to prevent fur-
ther increasing the transformer primary current.
The current-limit threshold can be adjusted using the
ILIM input. Connect a resistive voltage-divider between
V CC and GND with the midpoint connected to ILIM. The
current-limit threshold measured between LX_ and
GND is 1/5 of the voltage at ILIM. The ILIM adjustment
range is 0 to 3V. Connect ILIM to V CC to select the
default current-limit threshold of 0.2V.
VFB Undervoltage Protection
The MAX8722C incorporates a lamp VFB undervoltage
fault to comply with LCC test requirements (2k Ω short
across the transformer). The MAX8722C monitors the
lamp voltage feedback. If VFB is less than the VFB
undervolatge threshold (430mV) for more than the VFB
undervoltage protection timeout period, the MAX8722C
shutsdown.
The VFB undervoltage-protection timeout is generated
from the DPWM chopping frequency (f DPWM ), which is
set by the FREQ pin.
The timeout is given by: ((1/f DPWM )/128) x 14
With a typical DPWM chopping frequency of 210Hz, the
VFB undervoltage protection timeout will be 260μs.
For proper startup, ensure the lamp strikes before the
end of the VFB undervoltage-protection timeout period.
For applications that use an external DPWM chopping
frequency R FREQ is only used to set tha lamp under-
voltage timeout period.
Secondary Current Limit (ISEC)
The secondary current limit provides fail-safe current lim-
iting in case a failure, such as a short circuit or leakage
from the lamp high-voltage terminal to ground, prevents
the current control loop from functioning properly. ISEC
monitors the voltage across a sense resistor placed
between the transformer’s low-voltage secondary termi-
nal and ground. The ISEC voltage is internally half-wave
rectified and continuously compared to the ISEC regula-
tion threshold (1.20V typ). Any time the ISEC voltage
exceeds the threshold, a controlled current is drawn from
COMP to reduce the on-time of the bridge’s high-side
switches. At the same time, the MAX8722C charges the
TFLT capacitor with a 120 μA current source. The
MAX8722C latches off when the voltage on TFLT
exceeds 4V. Unlike the normal shutdown mode, the lin-
ear-regulator output (V CC ) remains at 5.4V. Toggling
SHDN or cycling the input power reactivates the device.
Linear-Regulator Output (V CC )
The internal linear regulator steps down the DC input
voltage to 5.4V (typ). The linear regulator supplies power
to the internal control circuitry of the MAX8722C and is
also used to power the MOSFET drivers by connecting
V CC to V DD . The V CC voltage drops to 4.6V in shutdown.
Applications Information
MOSFETs
The MAX8722C requires four external n-channel power
MOSFETs NL1, NL2, NH1, and NH2 to form a full-
bridge inverter circuit to drive the transformer primary.
The regulator senses the on-state drain-to-source volt-
age of the two low-side MOSFETs NL1 and NL2 to
detect the transformer primary current, so the R DS(ON)
of NL1 and NL2 should be matched. For instance, if
dual MOSFETs are used to form the full bridge, NL1
and NL2 should be in one package. Since the
MAX8722C uses the low-side MOSFET R DS(ON) for pri-
mary overcurrent protection, the lower the MOSFET
R DS(ON) , the higher the current limit. Therefore, the user
should select a dual, logic-level n-channel
MOSFET with low R DS(ON) to minimize conduction loss,
and keep the primary current limit at a reasonable level.
The regulator uses zero-voltage switching (ZVS) to soft-
ly turn on each of the four switches in the full bridge.
ZVS occurs when the external power MOSFETs are
turned on when their respective drain-to-source volt-
ages are near zero (see the Resonant Operation sec-
tion). ZVS effectively eliminates the instantaneous
turn-on loss of MOSFETs caused by C OSS (drain-to-
source capacitance) and parasitic capacitance dis-
charge, and improves efficiency and reduces
switching-related EMI.
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17
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相关代理商/技术参数 |
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| 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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