参数资料
型号: LT3757IDD#PBF
厂商: Linear Technology
文件页数: 23/36页
文件大小: 0K
描述: IC REG CTRLR BST FLYBK INV 10DFN
产品培训模块: LT3757 and LT3758 - Boost, Flyback, SEPIC and Inverting Controllers
标准包装: 121
PWM 型: 电流模式
输出数: 1
频率 - 最大: 1MHz
电源电压: 2.9 V ~ 40 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: 10-WFDFN 裸露焊盘
包装: 管件
LT3757/LT3757A
APPLICATIONS INFORMATION
V IN(MIN)
0.5 ? ? I SW ? f
Givenanoperatinginputvoltagerange,andhavingchosen
the operating frequency and ripple current in the inductor,
the inductor value (L1 and L2 are independent) of the SEPIC
converter can be determined using the following equation:
L1 = L2 = ? D MAX
For most SEPIC applications, the equal inductor values
will fall in the range of 1μH to 100μH.
Based on the preceding equations, the user should choose
the inductors having sufficient saturation and RMS cur-
rent ratings.
In a SEPIC converter, when the power switch is turned on,
the current flowing through the sense resistor (I SENSE ) is
the switch current.
Set the sense voltage at I SENSE(PEAK) to be the minimum
of the SENSE current limit threshold with a 20% margin.
The sense resistor value can then be calculated to be:
By making L1 = L2, and winding them on the same core, the
value of inductance in the preceding equation is replaced
by 2L, due to mutual inductance:
R SENSE =
80 mV
I SW(PEAK)
V IN(MIN)
? I SW ? f
L = ? D MAX
This maintains the same ripple current and energy storage
in the inductors. The peak inductor currents are:
I L1(PEAK) = I L1(MAX) + 0.5 ? ? I L1
I L2(PEAK) = I L2(MAX) + 0.5 ? ? I L2
The RMS inductor currents are:
SEPIC Converter: Power MOSFET Selection
For the SEPIC configuration, choose a MOSFET with a
V DC rating higher than the sum of the output voltage and
input voltage by a safety margin (a 10V safety margin is
usually sufficient).
The power dissipated by the MOSFET in a SEPIC con-
verter is:
P FET = I 2SW(MAX) ? R DS(ON) ? D MAX
? I L1
c L1 =
I L1(RMS) = I L1(MAX) ? 1 +
where:
I L1(MAX)
I L2(RMS) = I L2(MAX) ? 1 +
c 2L1
12
c 2L2
12
+ 2 ? ( V IN(MIN) + V OUT ) 2 ? I L(MAX) ? C RSS ? f /1A
The first term in this equation represents the conduction
losses in the device, and the second term, the switching
loss. C RSS is the reverse transfer capacitance, which is
usually specified in the MOSFET characteristics.
For maximum efficiency, R DS(ON) and C RSS should be
minimized. From a known power dissipated in the power
MOSFET, its junction temperature can be obtained using
the following equation:
where:
c L2 =
? I L2
I L2 (MAX)
T J = T A + P FET ? θ JA = T A + P FET ? ( θ JC + θ CA )
T J must not exceed the MOSFET maximum junction
temperature rating. It is recommended to measure the
MOSFET temperature in steady state to ensure that absolute
maximum ratings are not exceeded.
3757afd
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