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参数资料
| 型号： | MAX8785ETI+ |
| 厂商： | Maxim Integrated |
| 文件页数： | 15/19页 |
| 文件大小： | 0K |
| 描述： | IC CCFL CTRL 28-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 60 |
| 类型： | CCFL 控制器 |
| 电流 - 电源： | 1.5mA |
| 电源电压： | 4.5 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： | 管件 |
Full-Bridge Controller for
Piezoelectric Transformers
Open PZT Protection
The MAX8785A has protection against faulty connections
of PZT to the PC board. The OLF pin is used to detect
high-voltage conditions on the secondary side of the
minimize conduction loss, and keep the primary current
limit at a reasonable level. Use the following equation to
estimate the maximum and minimum values of the pri-
mary current limit:
transformer. When the OLF voltage exceeds 1.2V (typ), a
2.8mA current source starts charging the TFLT capacitor.
When V TFLT exceeds the threshold of 3V, the fault latch is
set and the MAX8785A stops switching. For details, see
I LIM _ MIN =
370 mV
R DS ( ON )_ MAX
the Setting the Arc Protection Threshold section.
Primary Side Current Limit
The MAX8785A senses the voltage across both low-
I LIM _ MAX =
430 mV
R DS ( ON )_ MIN
= I
× R
PD CONDUCT PRI DS ( ON )
2 × P OUT _ MAX
V IN _ MIN × η
I PRI =
side MOSFETs at LX1 and LX2. If the voltage exceeds
the internal 400mV (typ) current-limit threshold, the
MAX8785A turns off the respective MOSFET to prevent
the transformer primary current from increasing further.
Applications Information
MOSFETs
The MAX8785A requires four external n-channel power
MOSFETs to form a full-bridge inverter circuit to drive the
transformer primary. When selecting the MOSFET, focus
on the voltage rating, current rating, on-resistance
(R DS(ON) ), total gate charge, and power dissipation.
Select a MOSFET with a voltage rating at least 25% high-
er than the maximum input voltage of the inverter. For
example, if the maximum input voltage is 24V, the voltage
rating of the MOSFET should be 30V or higher. The cur-
rent rating of the MOSFET should be higher than the
peak primary current at the minimum input voltage and
full brightness. Use the following equation to estimate
the primary peak current I PEAK_PRI :
I PEAK _ PRI =
where P OUT_MAX is the maximum output power,
V IN_MIN is the minimum input voltage, and η the esti-
mated efficiency at the minimum input voltage, assum-
ing the full bridge drives one CCFL and maximum
output power of 4.5W. If the minimum input voltage is
8V and the estimated efficiency is 75% at that input, the
Both MOSFETs must be able to dissipate the conduction
losses, as well as 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
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 dissipa-
tion occurs where the conduction losses equal the
switching losses.
Calculate the total conduction power dissipation of the
two MOSFETs using the following equation:
2
where I PRI is the primary current calculated using the fol-
lowing equation and R DS(ON) is MOSFET on-resistance:
P OUT _ MAX
η × V IN
where P OUT_MAX is the output power of the lamp.
Both MOSFETs turn on with the ZVS condition, as the
switching frequency is the same as the resonance fre-
quency of the tank, so there is no switching power dis-
sipation associated with high-side MOSFET. However,
the current is at peak when the MOSFET is turned off.
Calculate the total turn-off switching power dissipation
of the two MOSFETs using the following equation:
peak primary current is approximately 1.1A. Therefore,
power MOSFETs with a DC current rating of 1.4A or
greater are sufficient.
Since the regulator senses the on-state, drain-to-source
PD SWTICH =
2 × C RSS × V IN 2 × f SW × I PRI
I GATE
voltage of both MOSFETs to detect the transformer
primary current, the lower the MOSFET R DS(ON) , the
higher the current limit would be. Therefore, the user
should select n-channel MOSFETs with low R DS(ON) to
where C RSS is the reverse transfer capacitance of the
MOSFETs, and I GATE is the peak gate-drive sink cur-
rent when the MOSFET is being turned off.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8785ETI+ | 功能描述:显示驱动器和控制器 Full-Bridge CCFL 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 |
| MAX8785ETI+T | 功能描述:显示驱动器和控制器 Full-Bridge CCFL 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 |
| MAX8785EVKIT | 功能描述:显示开发工具 MAX8785 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 |
| MAX8786GTL+ | 制造商:Maxim Integrated Products 功能描述:CONVERTOR - Bulk 制造商:Rochester Electronics LLC 功能描述: |
| MAX878LCSA | 制造商:Maxim Integrated Products 功能描述: |
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