参数资料
型号: SP7653ER-L
厂商: Exar Corporation
文件页数: 7/15页
文件大小: 0K
描述: IC REG BUCK SYNC ADJ 3A 26DFN
标准包装: 500
系列: Power Blox™
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 0.8 V ~ 19 V
输入电压: 2.5 V ~ 20 V
PWM 型: 电压模式
频率 - 开关: 1.3MHz
电流 - 输出: 3A
同步整流器:
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 26-VFDFN 裸露焊盘
包装: 散装
供应商设备封装: 26-DFN(7x4)
APPLICATIONS INFORMATION
I PEAK = I OUT (max) +
InductorSelection
There are many factors to consider in selecting
the inductor including core material, inductance
vs. frequency, current handling capability, effi-
ciency, size and EMI. In a typical SP7653 cir-
cuit, the inductor is chosen primarily for value,
saturation current and DC resistance. Increasing
the inductor value will decrease output voltage
ripple, but degrade transient response. Low in-
ductor values provide the smallest size, but
cause large ripple currents, poor efficiency and
require more output capacitance to smooth out
the larger ripple current. The inductor must be
able to handle the peak current at the switching
frequency without saturating, and the copper
resistance in the winding should be kept as low
as possible to minimize resistive power loss. A
good compromise between size, loss and cost is
to set the inductor ripple current to be within
20% to 40% of the maximum output current.
The switching frequency and the inductor oper-
ating point determine the inductor value as fol-
lows:
I PP
2
...and provide low core loss at the high switch-
ing frequency. Low cost powdered-iron cores
have a gradual saturation characteristic but can
introduce considerable AC core loss, especially
when the inductor value is relatively low and the
ripple current is high. Ferrite materials, although
more expensive, have an abrupt saturation char-
acteristic with the inductance dropping sharply
when the peak design current is exceeded. Nev-
ertheless, they are preferred at high switching
frequencies because they present very low core
loss while the designer is only required to
prevent saturation. In general, ferrite or
molypermalloy materials are a better choice for
all but the most cost sensitive applications.
Optimizing Efficiency
The power dissipated in the inductor is equal to
the sum of the core and copper losses. To mini-
mize copper losses, the winding resistance needs
to be minimized, but this usually comes at the
L =
V OUT ( V IN (max) V OUT )
V IN (max) F S K r I OUT ( max)
expense of a larger inductor. Core losses have a
more significant contribution at low output cur-
rent where the copper losses are at a minimum,
where:
f S = switching frequency
K r = ratio of the AC inductor ripple current to
the maximum output current
The peak-to-peak inductor ripple current is:
and can typically be neglected at higher output
currents where the copper losses dominate. Core
loss information is usually available from the
magnetics vendor. Proper inductor selection can
affect the resulting power supply efficiency by
more than 15%!
The copper loss in the inductor can be calculated
using the following equation:
I PP =
V OUT ( V IN (max) V OUT )
V I N (max) F S L
P L ( Cu ) = I L 2 ( RMS ) R WINDING
where I L(RMS) is the RMS inductor current that
can be calculated as follows:
( )
Once the required inductor value is selected, the
proper selection of core material is based on
peak inductor current and efficiency require-
I L(RMS) = I OUT(max) 1 + 1
3
I PP
I OUT(max)
2
ments. The core must be large enough not to
saturate at the peak inductor current...
2/17/06
Date:   /20/06
Wide Input Input     Range,Range,      BuckBuck
SP7653 SP7653 Wide Voltage Voltage  .3MHz, 1.3MHz, Regulator
7
? Copyright 2006 Sipex Corporation
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