参数资料
型号: LTC3538EDCB#TRPBF
厂商: Linear Technology
文件页数: 10/16页
文件大小: 0K
描述: IC REG BUCK BOOST SYNC ADJ 8DFN
标准包装: 2,500
类型: 降压(降压),升压(升压)
输出类型: 可调式
输出数: 1
输出电压: 1.8 V ~ 5.25 V
输入电压: 2.4 V ~ 5.5 V
频率 - 开关: 1MHz
电流 - 输出: 800mA
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: 8-WFDFN 裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 8-DFN(3x2)
LTC3538
OPERATION
V IN
During the period when the LTC3538 is delivering energy
to the output, the peak inductor current will be equal to
800mA typical and the inductor current will terminate
each cycle at zero current. In Burst Mode operation the
maximum average output current that can be delivered
while maintaining output regulation is given by:
I OUT _ BURST(BOOST) = 0.25 ? A; V OUT > V IN
V OUT
I OUT _ BURST(BUCK) = 0.27A; V OUT < V IN
The maximum average Burst Mode output current that
can be delivered in the four-switch buck-boost region is
limited to the boost equation speci?ed above.
INDUCTOR SELECTION
To achieve high ef?ciency, a low ESR inductor should be
utilized for the converter. The inductor must have a satura-
tion rating greater than the worst case average inductor
current plus half the ripple current. The peak-to-peak cur-
rent ripple will be larger in buck and boost mode than in
the buck-boost region. The peak-to-peak inductor current
ripple for each mode can be calculated from the following
formulas, where f is the frequency (1MHz typical) and L
is the inductance in μH.
In addition to affecting output current ripple, the size of the
inductor can also affect the stability of the feedback loop.
In boost mode, the converter transfer function has a right
half plane zero at a frequency that is inversely proportional
to the value of the inductor. As a result, a large inductor
can move this zero to a frequency low enough to degrade
the phase margin of the feedback loop. It is recommended
that the inductor value be chosen less than 10μH.
For high ef?ciency, choose a ferrite inductor with a high
frequency core material to reduce core loses. The induc-
tor should have low ESR (equivalent series resistance) to
reduce the I 2 R losses, and must be able to handle the peak
inductor current without saturating. Molded chokes or chip
inductors usually do not have enough core to support the
peak inductor currents in the 1A to 2A region. To minimize
radiated noise, use a shielded inductor. See Table 1 for a
suggested list of inductor suppliers.
Output Capacitor Selection
The bulk value of the output ?lter capacitor is selected to
reduce the ripple due to charge into the capacitor each
cycle. The steady state ripple due to charge is given by:
Δ V P-P, BOOST = I LOAD ? (V OUT – V IN )/(C OUT ? V OUT ? f)V
Δ V P-P,BUCK = (V IN – V OUT ) ? V OUT /(8 ? L ? V IN ? C OUT ? f 2 )V
V OUT ? ( V IN – V OUT ) / V IN
Δ I L,P-P,BUCK =
V OUT ? ( V OUT – V IN ) / V OUT
Δ I L,P-P,BOOST =
f?L
f ?L
where f = frequency (1MHz typical), Hz
L = inductor, H
Table 1. Inductor Vendor Information
A
A
where C OUT = output ?lter capacitor, F
I LOAD = Output load current, A
SUPPLIER
Coilcraft
CoEv Magnetics
Murata
PHONE
(847) 639-6400
(800) 227-7040
(814) 237-1431
FAX
(847) 639-1469
(650) 361-2508
(814) 238-0490
WEB SITE
www.coilcraft.com
www.tycoelectronics.com
www.murata.com
(800) 831-9172
Sumida
TDK
TOKO
USA: (847) 956-0666
Japan: 81 (3) 3607-5111
(847) 803-6100
(847) 297-0070
USA: (847) 956-0702
Japan: 81(3) 3607-5144
(847) 803-6296
(847) 699-7864
www.sumida.com
www.component.tdk.com
www.tokoam.com
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