参数资料
| 型号： | MAX8751ETJ+T |
| 厂商： | Maxim Integrated |
| 文件页数： | 21/27页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR CCFL INV 32-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： | 30 ~ 80 kHz |
| 电流 - 电源： | 3.2mA |
| 电源电压： | 6 V ~ 28 V |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 32-WFQFN 裸露焊盘 |
| 供应商设备封装： | 32-TQFN-EP（5x5） |
| 包装： | 带卷 (TR) |
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Fixed-Frequency, Full-Bridge CCFL
Inverter Controller
I LIM_MIN =
I LIM_MAX =
380mV
R DS(ON)_MAX
420mV
R DS(ON)_MIN
MOSFETs must be able to dissipate the conduction
Setting the Lamp Current
The MAX8751 senses the lamp current flowing through
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 full-wave recti-
fied. The MAX8751 controls the desired lamp current
by regulating the average of the rectified IFB voltage.
To set the RMS lamp current, determine R1 as follows:
losses plus the switching losses at both V IN_MIN and
V IN_MAX . Calculate both terms. Ideally, the losses at
V IN(MIN) should be roughly equal to the losses at
V IN(MAX) , with lower losses in between. If the losses at
R 1 =
π x 790 mV
2 2 x I LAMP ( RMS )
V IN(MIN) are significantly higher than the losses at
V IN(MAX) , consider increasing the size of the MOSFETs.
Conversely, if the losses at V IN(MAX) are significantly
higher than the losses at V IN(MIN) , consider choosing
MOSFETs with lower parasitic capacitance. If V IN does
not vary over a wide range, the minimum power dissi-
pation occurs where the conduction losses equal the
switching losses.
Calculate the total conduction power dissipation of the
two MOSFETs using the following equation:
PD CONDUCT = I PRI 2 xR DS ( ON )
where I PRI is the primary current calculated using the
following equation:
where I LAMP(RMS) is the desired RMS lamp current and
790mV 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 ? . The closest standard 1% resistors are 147 ?
and 150 ? . The precise shape of the lamp-current
waveform depends on lamp parasitics. The resulting
waveform is an imperfect sinusoid waveform, which has
an RMS value that is not easy to predict. A high-fre-
quency true RMS current meter (such as Yokogawa
2016) should be used to measure the RMS current and
make final adjustments to R1. Insert this meter between
the sense resistor and the lamp’s low-voltage terminal
to measure the actual RMS current.
Setting the Secondary Voltage Limit
The MAX8751 limits the transformer secondary voltage
during startup and lamp-out faults. The secondary volt-
age is sensed through the capacitive voltage-divider
I PRI =
P OUT _ MAX
η x V IN
formed by C3 and C4 (Figure 1). The voltage of VFB is
proportional to the CCFL voltage. The selection of the
parallel resonant capacitor C1 is described in the
Selecting the Resonant Components section. Smaller
The low-side MOSFETs turn on with ZVS. If the switch-
ing frequency is close to resonant frequency, turn-on
power loss associated with high-side MOSFETs can be
ignored. However, the current is at peak when the
MOSFET is turned off. Calculate the turn-off switching
power dissipation of the MOSFET using the following
equation:
values for C3 result in higher efficiency due to lower cir-
culating current. If C3 is too small, the resonant opera-
tion is affected by the panel parasitic capacitance.
Therefore, C3 is usually chosen to be between 10pF
and 18pF. After the value of C3 is set, select C4 based
on the desired maximum RMS secondary voltage
V LAMP(RMS)_MAX :
PD SWITCH =
2 x C RSS x V IN 2 x f SW x I PRI
I GATE
C4 =
2 x V LAMP(RMS)_MAX
2.32V
x C3
where the 2.34V is the typical value of the VFB peak
where C RSS is the reverse transfer capacitance of the
MOSFETs and I GATE is the peak gate-drive sink current
when the MOSFET is being turned off.
voltage when the lamp is open. To set the maximum
RMS secondary voltage to 1800V with C3 selected to
be 12pF, C4 must be less than or equal to 13nF.
______________________________________________________________________________________
21
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| MAX8751EVKIT | 功能描述:电源管理IC开发工具 MAX8751 Eval Kit RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
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