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| 型号： | ISL6844EVAL2 |
| 厂商： | Intersil |
| 文件页数： | 2/12页 |
| 文件大小： | 0K |
| 描述： | EVALUATION BOARD 2 ISL6844 |
| 标准包装： | 1 |
| 主要目的： | 特殊用途 DC/DC，以太网供电（POE） |
| 输出及类型： | 1，隔离 |
| 功率 - 输出： | 11W |
| 输出电压： | 3.3V |
| 电流 - 输出： | 3.35A |
| 输入电压： | 36 ~ 57V |
| 稳压器拓扑结构： | 回扫 |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | ISL6844 |
Application Note 1192
Primary MOSFET Selection
The primary MOSFET needs to be able to handle the peak
seen at minimum duty cycle (maximum input voltage). The
minimum and maximum duty cycle can be calculated by:
= 57 + [ 6 × ( 3.3 + 0.4 ) ] = 79.2V
? 3.3 - × 6 ?
? ------------------- × N ps ?
V inmax
? ?
? 57
?
D min = --------------------------------------------------------- = -------------------------------------- = 0.2578
V out
1 + ? -------- × 6 ?
1 + ? ------------------- × N ps ? ? 57 ?
V f
? 3.3 - × 6 ?
? ------------------ × N ps ?
? V inmin
?
? 36
?
D max = -------------------------------------------------------- = -------------------------------------- = 0.355
? V out
1 + ? -------- × 6 ?
1 + ? ------------------ × N ps ? ? 36 ?
V DSFET sec ondary = ------------- = ------------------ = 12.8V
voltage stress on the primary of a flyback design, given by:
V DSFETprimary = V DSFETprimary + [ N ps × ( V out + V f ) ]
(EQ. 1)
where
N ps = Turns ratio between the primary and the secondary
windings
V out = Output Voltage
= Forward drop across the diode (negligible in the case
of synchronous rectification)
As a good design practice, some margin is provided to this
peak stress voltage to accommodate transient spikes and for
a good reliable performance over time. Providing a 30%
design margin as a rule of thumb, the minimum rating on the
primary MOSFET needs to be 103V. HAT2088R-EL-E, a
? V out ?
-------
? ? 3.3
? V inmax ?
? V out ?
-------
? 3.3
? V inmin ?
The peak voltage can then be calculated by:
V out 3.3
D min
(EQ. 2)
(EQ. 3)
(EQ. 4)
Isp = ? ---------------------------- × --------------- × N ps ? + ? --------------------------------------- × --- ?
V inmin × η
D max
? ?
= ? -------------------------- × --------------- × 6 ? + ? ------------------------------------------------------------- × --- ?
155 × 10
× 200 × 10
200V part, was selected for the purpose, taking into account
also that this part has a very low capacitance and a very low
gate charge, key to keep the power losses to a minimum.
Rectification
Two versions of the evaluation board are available:
? A synchronous rectified output, with the converter
operating in the continuous current mode, to attain the
high efficiency target. This version is available as
ISL6844EVAL1Z. For this implementation, a discrete gate
drive circuit was designed, using a gate drive transformer
to meet isolation requirements.
? A conventionally rectified version, ISL6844EVAL2Z, is
also available for end users to whom tight regulation is not
critical, but emphasis is on cost saving at the expense of
slightly reduced efficiency. Since the feedback is tapped
off the primary auxiliary winding in this application, the
Providing a 30% design margin on similar grounds to the
primary FET selection, the minimum rating on the secondary
MOSFET is about 17V. To achieve the right balance
between the low r DS(ON) , to minimize conduction losses,
and low Q g , to minimize switching losses, HAT2168H-EL-E,
a 30V device was chosen.
Output Filter
The output capacitance needs to meet the ripple and noise
requirements, and also be able to handle the ripple current.
The peak secondary current can be approximately
calculated using the formula given in EQ. 5 below:
? V out × I out 1 ? V inmin × D max 1
? L × fsw 2 ?
3.3 × 3.35 1 36 × 0.355 1
? 36 × 0.87 0.355 ? ? – 6 3 2 ?
varying diode drop with load results in slightly lower
regulation. In the case of a synchronous rectified output,
the drop across the switching device is negligible. The
conventionally rectified version also operates in the
continuous current mode to maximize efficiency, and lower
the output ripple.
Secondary MOSFET Selection
The secondary MOSFET selection follows slightly different
criteria. The emphasis here is more to reduce the DC losses,
and hence a very low r DS(ON) device is required. At the
same time, care needs to be taken to ensure that the gate
charge required to drive the FET is not too large, as this may
need a beefy gate drive circuit. The peak voltage will be
2
= 6.2A
where
I sp = Peak Secondary Current
I sp = Efficiency of the Converter
f sw = Switching Frequency of the Converter
L = Magnetizing Inductance of the Transformer
(EQ. 5)
AN1192.3
March 12, 2007
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相关代理商/技术参数 |
参数描述 |
|---|---|
| ISL6844EVAL3Z | 制造商:Intersil Corporation 功能描述:ISL6844 EVALUATION BOARD 3 - 8 LEAD - MSOP -ROHS COMPLIANT - Bulk 制造商:Intersil Corporation 功能描述:BOARD EVAL FOR ISL6844 |
| ISL6844IB | 功能描述:电流型 PWM 控制器 Single-End Current RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| ISL6844IB-T | 功能描述:IC REG CTRLR BST FLYBK ISO 8SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:100% 电源电压:8.2 V ~ 30 V 降压:无 升压:无 回扫:是 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:是 工作温度:0°C ~ 70°C 封装/外壳:8-DIP（0.300"，7.62mm） 包装:管件 产品目录页面:1316 (CN2011-ZH PDF) |
| ISL6844IBZ | 功能描述:电流型 PWM 控制器 CUR MODE PWM 50% DUT Y CYCLE 14.5V UVLO RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| ISL6844IBZ-T | 功能描述:IC REG CTRLR BST FLYBK ISO 8SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:275kHz 占空比:50% 电源电压:18 V ~ 110 V 降压:无 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:是 工作温度:-40°C ~ 85°C 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) |
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