参数资料
型号: LTC3631EMS8E#PBF
厂商: Linear Technology
文件页数: 11/22页
文件大小: 0K
描述: IC REG BUCK SYNC ADJ 0.1A 8MSOP
标准包装: 50
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 0.8 V ~ 45 V
输入电压: 4.5 V ~ 45 V
PWM 型: Burst Mode?
电流 - 输出: 100mA
同步整流器:
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 8-TSSOP,8-MSOP(0.118",3.00mm 宽)裸露焊盘
包装: 管件
供应商设备封装: 8-MSOP-EP
产品目录页面: 1335 (CN2011-ZH PDF)
LTC3631
APPLICATIONS INFORMATION
700
600
500
400
V OUT = 5V
I SET OPEN
L = 22μH
L = 47μH
where board area is not a limiting factor, inductors with
larger cores can be used, which extends the recommended
range of Figure 4 to larger values.
Inductor Core Selection
V OUT = 3.3V
I SET OPEN
150
L = 220μH
300
L = 100μH
200
L = 220μH
100
0
5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
3631 F02
Figure 2. Switching Frequency for V OUT = 5V
500
450
L = 22μH
400
350
300 L = 47μH
250
200
L = 100μH
100
50
0
5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
3631 F03
Figure 3. Switching Frequency for V OUT = 3.3V
10000
1000
Once the value for L is known, the type of inductor must
be selected. High efficiency converters generally cannot
afford the core loss found in low cost powdered iron cores,
forcing the use of the more expensive ferrite cores. Actual
core loss is independent of core size for a fixed inductor
value but is very dependent of the inductance selected.
As the inductance increases, core losses decrease. Un-
fortunately, increased inductance requires more turns of
wire and therefore copper losses will increase.
Ferrite designs have very low core losses and are pre-
ferred at high switching frequencies, so design goals
can concentrate on copper loss and preventing satura-
tion. Ferrite core material saturates “hard,” which means
that inductance collapses abruptly when the peak design
current is exceeded. This results in an abrupt increase in
inductor ripple current and consequently output voltage
ripple. Do not allow the core to saturate!
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 materials are
small and do not radiate energy but generally cost more
than powdered iron core inductors with similar charac-
teristics. The choice of which style inductor to use mainly
depends on the price vs size requirements and any radiated
field/EMI requirements. New designs for surface mount
inductors are available from Coiltronics, Coilcraft, TDK,
Toko, Sumida and Vishay.
C IN and C OUT Selection
100
10
10
100
1000
The input capacitor, C IN , is needed to filter the trapezoidal
current at the source of the top high side MOSFET. To
prevent large ripple voltage, a low ESR input capacitor
sized for the maximum RMS current should be used.
Approximate RMS current is given by:
PEAK INDUCTOR CURRENT (mA)
3631 F04
Figure 4. Recommended Inductor Values for Maximum Efficiency
I RMS = I OUT(MAX) ?
V OUT
V IN
?
V IN
V OUT
? 1
3631fe
For more information www.linear.com/LTC3631
11
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