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参数资料
| 型号： | LT3957EUHE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 17/28页 |
| 文件大小： | 0K |
| 描述： | IC REG MULTI CONFIG ADJ 36VQFN |
| 特色产品： | LT?3957/LT?3958 Converters |
| 标准包装： | 61 |
| 类型： | 升压（升压），反相，回扫，Sepic |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.6 V ~ 40 V |
| 输入电压： | 3 V ~ 40 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 100kHz ~ 1MHz |
| 电流 - 输出： | 5A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 36-WFQFN 裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 36-QFN-EP（6x5） |
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LT3957
APPLICATIONS INFORMATION
N P 40V ? V IN(MAX)
N S
k ? V OUT
? D MAX ? ( 5A ? 0.5 ? Δ I SW )
I O(MAX) <
AccordingtotheAbsoluteMaximumRatingstable,theSW
voltage Absolute Maximum value is 40V. Therefore, the
maximum primary to secondary turns ratio (for both the
continuous and the discontinuous operation) should be.
≤
According to the preceding equations, the user has relative
freedom in selecting the switch duty cycle or turns ratio to
suit a given application. The selections of the duty cycle
and the turns ratio are somewhat iterative processes, due
to the number of variables involved. The user can choose
either a duty cycle or a turns ratio as the start point. The
following trade-offs should be considered when select-
ing the switch duty cycle or turns ratio, to optimize the
converter performance. A higher duty cycle affects the
?yback converter in the following aspects:
? Lower MOSFET RMS current I SW(RMS) , but higher
MOSFET V SW peak voltage
output current capability by a suf?cient margin (10% or
higher is recommended):
V IN(MIN)
V OUT
The transformer ripple current Δ I SW has a direct effect on
the design/choice of the transformer and the converter’s
output current capability. Choosing smaller values of
Δ I SW increases the output current capability, but requires
large primary and secondary inductances and reduce the
current loop gain (the converter will approach voltage
mode). Accepting larger values of Δ I SW allows the use
of low primary and secondary inductances, but results
in higher input current ripple, greater core losses, and
reduces the output current capability.
Given an operating input voltage range, and having chosen
the operating frequency and ripple current in the primary
winding, the primary winding inductance can be calculated
using the following equation:
? Lower diode peak reverse voltage, but higher diode
RMS current I D(RMS)
? Higher transformer turns ratio (N P /N S )
L =
V IN(MIN)
Δ I SW ? ?
? D MAX
It is recommended to choose a duty cycle between 20%
and 80%.
The primary winding peak current is the switch current
limit (typical 5.9A). The primary and secondary maximum
RMS currents are:
Flyback Converter: Maximum Output Current
Capability and Transformer Design
The maximum output current capability and transformer
design for continuous conduction mode (CCM) is chosen
as presented here.
I LP(RMS) ≈
I LS(RMS) ≈
P OUT(MAX)
D MAX ? V IN(MIN) ? η
I OUT(MAX)
1 ? D MAX
V OUT ? ? P ?
D MAX =
V OUT ? ? P ? + V IN(MIN)
Themaximumdutycycle(D MAX )occurswhentheconverter
has the minimum V IN :
? N ?
? N S ?
? N ?
? N S ?
Due to the current limit of its internal power switch, the
LT3957 should be used in a ?yback converter whose maxi-
mum output current (I O(MAX) ) is less than the maximum
where η is the converter ef?ciency.
Based on the preceding equations, the user should de-
sign/choose the transformer having suf?cient saturation
and RMS current ratings.
Flyback Converter: Snubber Design
Transformer leakage inductance (on either the primary or
secondary) causes a voltage spike to occur after the MOS-
FET turn-off. This is increasingly prominent at higher load
currents, where more stored energy must be dissipated.
3957f
17
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3957EUHETRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch |
| LT3957IUHE#PBF | 功能描述:IC REG MULTI CONFIG ADJ 36VQFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT3957IUHE#TRPBF | 功能描述:IC REG MULTI CONFIG ADJ 36VQFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT3957IUHEPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch |
| LT3957IUHETRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch |
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