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| 型号： | LTC3408EDD |
| 厂商： | Linear Technology |
| 文件页数： | 8/12页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK W/BYPASS TXRX 8-DFN |
| 标准包装： | 121 |
| 应用： | 转换器，WCDMA 功率放大器应用 |
| 输入电压： | 2.5 V ~ 5 V |
| 输出数： | 1 |
| 输出电压： | 0.3 V ~ 3.5 V |
| 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 |
| 供应商设备封装： | 8-DFN-EP（3x3） |
| 包装： | 管件 |
LTC3408
APPLICATIO S I FOR ATIO
At output voltages below 0.6V, the switching frequency
decreases linearly to a minimum of approximately 700kHz.
maximum RMS current must be used. The maximum
RMS capacitor current is given by:
This places the maximum ripple current (in forced con-
tinuous mode) at the highest input voltage and the lowest
output voltage. In practice, the resulting ouput ripple
C IN required I RMS ? I OMAX
[ V OUT ( V IN – V OUT )] 1 / 2
V IN
voltage is 10mV to 15mV using the components specified
in Figure 1.
The DC current rating of the inductor should be at least equal
to the maximum load current plus half the ripple current to
prevent core saturation. Thus, a 660mA rated inductor
should be enough for most applications (600mA + 60mA).
For better efficiency, choose a low DC-resistance inductor.
Inductor Core Selection
Different core materials and shapes will change the size/
current and price/current relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy mate-
rials are small and don’t radiate much energy but generally
cost more than powdered iron core inductors with similar
This formula has a maximum at V IN = 2V OUT , where I RMS
= I OUT /2. This simple worst-case condition is commonly
used for design because even significant deviations do not
offer much relief. Note that the capacitor manufacturer’s
ripple current ratings are often based on 2000 hours of life.
This makes it advisable to further derate the capacitor, or
choose a capacitor rated at a higher temperature than re-
quired. Always consult the manufacturer if there is any
question.
The selection of C OUT is driven by the required effective
series resistance (ESR). Typically, once the ESR
requirement for C OUT has been met, the RMS current
rating generally far exceeds the I RIPPLE(P-P) requirement.
The output ripple V OUT is determined by:
? V OUT L ? ESR +
electricalcharacteristics.Thechoiceofwhichstyleinduc-
tor to use often depends more on the price versus size
requirements and any radiated field/EMI requirements
? ? I
?
?
1 ?
8 f C OUT ? ?
than on what the LTC3408 requires to operate. Table 1
shows some typical surface mount inductors that work
well in LTC3408 applications.
Table 1. Representative Surface Mount Inductors
PART VALUE DCR MAX DC SIZE
NUMBER ( μ H) ( ? MAX) CURRENT (A) WxLxH (mm 3 )
where f = operating frequency, C OUT = output capacitance
and I L = ripple current in the inductor. For a fixed output
voltage, the output ripple is highest at maximum input
voltage since I L increases with input voltage.
Aluminum electrolytic and dry tantalum capacitors are
Sumida
CDRH2D11
Sumida
CDRH2D18/LD
Sumida
4.7
4.7
4.7
0.135
0.078
0.216
0.5
0.63
0.75
3.2 x 3.2 x 1.2
3.2 x 3.2 x 2.0
3.5 x 4.1 x 0.8
both available in surface mount configurations. In the case
of tantalum, it is critical that the capacitors are surge tested
for use in switching power supplies. An excellent choice is
the AVX TPS series of surface mount tantalum. These are
CMD4D06
specially constructed and tested for low ESR so they give
Murata
LQH32C
Taiyo Yuden
LBLQ2016
Toko
4.7
4.7
4.7
0.150
0.250
0.20
0.65
0.210
0.79
2.5 x 3.2 x 2.0
1.6 x 2.0 x 1.6
3.6 x 3.6 x 1.2
the lowest ESR for a given volume. Other capacitor types
include Sanyo POSCAP, Kemet T510 and T495 series, and
Sprague 593D and 595D series. Consult the manufacturer
for other specific recommendations.
D312C
C IN and C OUT Selection
In continuous mode, the source current of the top MOSFET
is a square wave of duty cycle V OUT /V IN . To prevent large
voltage transients, a low ESR input capacitor sized for the
The bulk capacitance values in Figure 1(a) (C IN = 10 μ F,
C OUT = 4.7 μ F) are tailored to mobile phone applications, in
which the output voltage is expected to slew quickly
according to the needs of the power amplifier. Holding the
output capacitor to 4.7 μ F facilitates rapid charging and
discharging. When the output voltage descends quickly in
3408f
8
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| LTC3408EDD#PBF | 功能描述:IC REG BUCK W/BYPASS TXRX 8-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 专用型 系列:- 标准包装:43 系列:- 应用:控制器，Intel VR11 输入电压:5 V ~ 12 V 输出数:1 输出电压:0.5 V ~ 1.6 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:48-VFQFN 裸露焊盘 供应商设备封装:48-QFN（7x7） 包装:管件 |
| LTC3408EDD#TR | 功能描述:IC REG BUCK W/BYPASS TXRX 8-DFN RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - 专用型 系列:- 标准包装:43 系列:- 应用:控制器，Intel VR11 输入电压:5 V ~ 12 V 输出数:1 输出电压:0.5 V ~ 1.6 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:48-VFQFN 裸露焊盘 供应商设备封装:48-QFN（7x7） 包装:管件 |
| LTC3408EDD#TRPBF | 功能描述:IC REG BUCK W/BYPASS TXRX 8-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 专用型 系列:- 标准包装:43 系列:- 应用:控制器，Intel VR11 输入电压:5 V ~ 12 V 输出数:1 输出电压:0.5 V ~ 1.6 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:48-VFQFN 裸露焊盘 供应商设备封装:48-QFN（7x7） 包装:管件 |
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| LTC3409A | 制造商:LINER 制造商全称:Linear Technology 功能描述:600mA Low VIN Buck Regulator in 3mm × 3mm DFN |
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