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| 型号： | LT3957EUHE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 19/28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
V OUT + V D D
V IN
1 ? D
I L1(MAX) = I IN(MAX) = I O(MAX) ?
SEPIC CONVERTER APPLICATIONS
The LT3957 can be con?gured as a SEPIC (single-ended
primary inductance converter), as shown in Figure 1. This
topology allows for the input to be higher, equal, or lower
than the desired output voltage. The conversion ratio as
a function of duty cycle is:
=
in continuous conduction mode (CCM).
In a SEPIC converter, no DC path exists between the input
and output. This is an advantage over the boost converter
for applications requiring the output to be disconnected
from the input source when the circuit is in shutdown.
Compared to the ?yback converter, the SEPIC converter
has the advantage that both the power MOSFET and the
output diode voltages are clamped by the capacitors (C IN ,
C DC and C OUT ), therefore, there is less voltage ringing
across the power MOSFET and the output diodes. The
SEPIC converter requires much smaller input capacitors
than those of the ?yback converter. This is due to the fact
that, in the SEPIC converter, the current through inductor
L1 (which is series with the input) is continuous.
SEPIC Converter: Switch Duty Cycle and Frequency
For a SEPIC converter operating in CCM, the duty cycle
of the main switch can be calculated based on the output
voltage (V OUT ), the input voltage (V IN ) and the diode
forward voltage (V D ).
The maximum duty cycle (D MAX ) occurs when the converter
has the minimum input voltage:
can also be wound on the same core, since identical volt-
ages are applied to L1 and L2 throughout the switching
cycle.
For the SEPIC topology, the current through L1 is the
converter input current. Based on the fact that, ideally, the
output power is equal to the input power, the maximum
average inductor currents of L1 and L2 are:
D MAX
1 ? D MAX
I L2(MAX) = I O(MAX)
Due to the current limit of its internal power switch,
the LT3957 should be used in a SEPIC converter whose
maximum output current (I O(MAX) ) is less than the output
current capability by a suf?cient margin (10% or higher
is recommended):
I O(MAX) < ( 1 ? D MAX ) ? ( 5A ? 0.5 ? Δ I SW )
The inductor ripple currents Δ I L1 and Δ I L2 are identical:
Δ I L1 = Δ I L2 = 0.5 ? Δ I SW
The inductor ripple current Δ I SW has a direct effect on the
choice of the inductor value and the converter’s maximum
output current capability. Choosing smaller values of Δ I SW
requires large inductances and reduces the current loop
gain (the converter will approach voltage mode). Accepting
larger values of Δ I SW allows the use of low inductances,
but results in higher input current ripple and greater core
losses and reduces output current capability.
Given an operating input voltage range, and having chosen
the operating frequency and ripple current in the induc-
D MAX =
V OUT + V D
V IN(MIN) + V OUT + V D
tor, the inductor value (L1 and L2 are independent) of the
SEPIC converter can be determined using the following
equation:
SEPIC Converter: The Maximum Output Current
Capability and Inductor Selection
L1 = L2 =
V IN(MIN)
0.5 ? Δ I SW ? ?
? D MAX
As shown in Figure 1, the SEPIC converter contains two
inductors: L1 and L2. L1 and L2 can be independent, but
For most SEPIC applications, the equal inductor values
will fall in the range of 1μH to 100μH.
3957f
19
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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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