参数资料
| 型号： | MAX8709BETI+T |
| 厂商： | Maxim Integrated |
| 文件页数： | 20/24页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR CCFL HI EFF 28-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 类型： | CCFL 控制器 |
| 频率： | 25 ~ 300 kHz |
| 电流 - 电源： | 1.5mA |
| 电流 - 输出： | 500mA |
| 电源电压： | 4.6 V ~ 28 V |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 28-WFQFN 裸露焊盘 |
| 供应商设备封装： | 28-TQFN-EP（5x5） |
| 包装： | 带卷 (TR) |
High-Efficiency CCFL Backlight
Controller with SMBus Interface
R 1 =
C 4 = ? - 1 ? × C 3
?
?
Applications Information
To select the correct component values for the
MAX8709B, several CCFL parameters must be specified.
(Table 7).
MOSFETs
The MAX8709B 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 regu-
lator senses the on-state drain-to-source voltage of the
two low-side MOSFETs NL1 and NL2 to detect the trans-
former 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. Select dual logic-level n-channel MOSFETs
with low R DS(ON) to minimize conduction loss for
NL1/NL2 and NH1/NH2. The regulator utilizes the energy
stored in the transformer’s primary leakage inductance to
softly turn on each of four switches in the full bridge ZVS
occurs when the external power MOSFETs are turned on
when their respective drain-to-source voltages are near
0V. ZVS effectively eliminates the instantaneous turn-on
loss of MOSFETs caused by C OSS (drain-to-source
capacitance) and parasitic capacitance discharge, and
improves efficiency and reduces switching-related EMI.
Setting the Lamp Current
The MAX8709B senses the lamp current flowing through
a resistor R1 (Figure 1) connected between the low-volt-
age terminal of the lamp and ground. The voltage across
R1 is fed to IFB and is internally rectified. The MAX8709B
controls the desired lamp current by regulating the
average of the half-wave rectified IFB voltage. To set
the RMS lamp current, determine R1 as follows:
π × 400 mV
2 × I LAMP ( RMS )
where I LAMP(RMS) is the desired RMS lamp current and
400mV is the typical value of the IFB regulation point
specified in the Electrical Characteristics table. To set
the RMS lamp current to 6mA, the value of R1 should
be 148 Ω . The closest standard 1% resistors are 147 Ω
and 150 Ω . The precise shape of the lamp-current
waveform, which is dependent on lamp parasitics, influ-
ences the actual RMS lamp current. Use a true RMS
current meter to make final adjustments to R1.
Setting the Secondary Voltage Limit
The MAX8709B limits the transformer secondary voltage
during lamp striking and lamp-out faults. The secondary
voltage is sensed through the capacitive voltage-divider
formed by C3 and C4 (Figure 1). The voltage on VFB is
proportional to the CCFL voltage. The selection of the
parallel resonant capacitor C3 is described in the
Transformer Design and Resonant Component Selection
section. C3 is usually between 10pF to 22pF. After the
value of C3 is determined, select C4 using the following
equation to set the desired maximum RMS secondary
voltage V LAMP(RMS) _ MAX :
? 2 × V LAMP ( RMS )_ MAX ?
? π × 510 mV ?
where 510mV is the typical value of the VFB regulation
threshold specified in the Electrical Characteristics
Table 7. CCFL Specifications
SPECIFICATION
CCFL Minimum
Striking Voltage
(Kick-Off Voltage)
CCFL Typical
Operating Voltage
(Lamp Voltage)
CCFL Operating
Current
(Lamp Current)
CCFL Maximum
Frequency
(Lamp Frequency)
SYMBOL
V STRIKE
V LAMP
I LAMP
f
UNITS
V RMS
V RMS
mA RMS
kHz
DESCRIPTION
Although CCFLs typically operate at less than 550V RMS , a higher voltage (1000V RMS
and up) is required initially to start the tube. The strike voltage is typically higher at
cold temperatures and at the end of life of the tube. Resonant operation and the
high Q of the resonant tank generate the required strike voltage of the lamp.
Once a CCFL has been struck, the lamp voltage required to maintain light output
falls to approximately 550V RMS . Short tubes may operate on as little as 250V RMS .
The operating voltage of the CCFL stays relatively constant, even as the tube’s
brightness is varied.
The desired RMS AC current through a CCFL is typically 6mA RMS . DC current is not
allowed through CCFLs. The sense resistor, R1, sets the lamp current.
The maximum AC-lamp-current frequency. The circuit should be designed to
operate the lamp below this frequency. The MAX8709B is designed to operate
between 20kHz and 100kHz.
20
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8709ETI | 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 |
| MAX8709ETI+ | 功能描述:显示驱动器和控制器 CCFL Backlight Controller w/SMBus 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 |
| MAX8709ETI+T | 功能描述:显示驱动器和控制器 CCFL Backlight Controller w/SMBus 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 |
| MAX8709ETI-T | 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 |
| MAX8709EVKIT | 功能描述:显示开发工具 MAX8709 Eval Kit RoHS:否 制造商:4D Systems 产品:4Display Shields 工具用于评估:?OLED-160-G1, ?OLED-160-G2 接口类型:Serial 工作电源电压:5 V |
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