參數(shù)資料
型號(hào)： LT3957EUHE#TRPBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： SWITCHING REGULATOR, PQCC36
封裝： 5 X 6 MM, LEAD FREE, PLASTIC, QFN-36
文件頁(yè)數(shù)： 9/28頁(yè)
文件大?。?/td> 359K
代理商： LT3957EUHE#TRPBF
LT3957
17
3957f
APPLICATIONS INFORMATION
According to the Absolute Maximum Ratings table, the SW
voltage Absolute Maximum value is 40V. Therefore, the
maximum primary to secondary turns ratio (for both the
continuous and the discontinuous operation) should be.
NP
NS
≤
40V VIN(MAX)
k VOUT
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 ISW(RMS), but higher
MOSFET VSW peak voltage
Lower diode peak reverse voltage, but higher diode
RMS current ID(RMS)
Higher transformer turns ratio (NP/NS)
It is recommended to choose a duty cycle between 20%
and 80%.
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.
The maximum duty cycle (DMAX)occurswhentheconverter
has the minimum VIN:
DMAX =
VOUT
NP
NS
VOUT
NP
NS
+ VIN(MIN)
Due to the current limit of its internal power switch, the
LT3957 should be used in a yback converter whose maxi-
mum output current (IO(MAX)) is less than the maximum
output current capability by a sufcient margin (10% or
higher is recommended):
IO(MAX) <
VIN(MIN)
VOUT
DMAX 5A 0.5 ΔISW
(
)
The transformer ripple current
ΔISW has a direct effect on
the design/choice of the transformer and the converter’s
output current capability. Choosing smaller values of
ΔISW 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
ΔISW 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:
L =
VIN(MIN)
ΔISW
DMAX
The primary winding peak current is the switch current
limit (typical 5.9A). The primary and secondary maximum
RMS currents are:
ILP(RMS) ≈
POUT(MAX)
DMAX VIN(MIN) η
ILS(RMS) ≈
IOUT(MAX)
1DMAX
where
η is the converter efciency.
Based on the preceding equations, the user should de-
sign/choose the transformer having sufcient 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.
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LT3957IUHE#PBF 功能描述:IC REG MULTI CONFIG ADJ 36VQFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開關(guān):- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤
LT3957IUHE#TRPBF 功能描述:IC REG MULTI CONFIG ADJ 36VQFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開關(guān):- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤
LT3957IUHEPBF 制造商:LINER 制造商全稱:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch
LT3957IUHETRPBF 制造商:LINER 制造商全稱:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch
LT3958 制造商:LINER 制造商全稱:Linear Technology 功能描述:Monolithic High Voltage Isolated Flyback Converter No External Start-Up Resistor
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