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| 型号： | LT1111CS8-5#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BST INV 5V .4A 8SOIC |
| 标准包装： | 100 |
| 类型： | 降压（降压），升压（升压），反相 |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 5V |
| 输入电压： | 2 V ~ 30 V |
| 频率 - 开关： | 72kHz |
| 电流 - 输出： | 400mA |
| 同步整流器： | 无 |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 供应商设备封装： | 8-SOIC |
| 产品目录页面： | 1325 (CN2011-ZH PDF) |
LT1111
A PPLICATI
S I FOR ATIO
switch closes, current in the inductor builds according to
specifically designed for switch mode DC/DC converters
which work much better than general-purpose units.
?
? 1 – e
R ′ ?
?
I L
t
() =
V L
?
– R ′ t ?
L ?
?
( 15 )
Tantalum capacitors provide still better performance at
more expense. We recommend OS-CON capacitors from
Sanyo Corporation (San Diego, CA). These units are
physically quite small and have extremely low ESR. To
where R ′ = 0.65 ? + DCR L
V L = V IN – 0.75V
As an example, suppose –5V at 50mA is to be generated
from a 4.5V to 5.5V input. Recalling Equation (14),
illustrate, Figures 1, 2, and 3 show the output voltage of an
LT1111 based converter with three 100 μ F capacitors. The
peak switch current is 500mA in all cases. Figure 1 shows
a Sprague 501D, 25V aluminum capacitor. V OUT jumps by
over 120mV when the switch turns off, followed by a drop
P L = ( ? -5V ? +0.5V )( 50mA ) = 275mW
(16)
in voltage as the inductor dumps into the capacitor. This
works out to be an ESR of over 0.24 ? . Figure 2 shows the
= = 3 . 8 μ J .
P L 275 mW
Energy required from the inductor is:
( 17 )
f OSC 72 kHz
Picking an inductor value of 56 μ H with 0.2 ? DCR results
in a peak switch current of:
same circuit, but with a Sprague 150D, 20V tantalum
capacitor replacing the aluminum unit. Output jump is
now about 35mV, corresponding to an ESR of 0.07 ? .
Figure 3 shows the circuit with a 16V OS-CON unit. ESR
is now only 0.02 ? .
( ) V ? ? 1 – e – 0 . 85 56 ? μ × H 7 μ s ? ? = 445 mA .
( ) ? ? ?
0 . 65 ? + 0 . 2
?
?
I PEAK =
4 . 5 V – 0 . 75
(18)
Substituting I PEAK into Equation (4) results in:
5 μ s/DIV
Figure 1. Aluminum
LT1111 ? F01
E L =
1
2
(
56 μ H )( 0 . 445 A
) 2 = 5 . 54 μ J .
( 19 )
Since 5.54 μ J > 3.82 μ J, the 56 μ H inductor will work.
With this relatively small input range, R LIM is not usually
necessary and the I LIM pin can be tied directly to V IN . As in
the step-down case, peak switch current should be limited
to ~650mA.
Capacitor Selection
Selecting the right output capacitor is almost as important
as selecting the right inductor. A poor choice for a filter
capacitor can result in poor efficiency and/or high output
ripple. Ordinary aluminum electrolytics, while inexpensive
and readily available, may have unacceptably poor
equivalent series resistance (ESR) and ESL (inductance).
There are low ESR aluminum capacitors on the market
5 μ s/DIV
Figure 2. Tantalum
5 μ s/DIV
Figure 3. OS-CON
LT1111 ? F02
LT1111 ? F01
1111fd
9
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相关代理商/技术参数 |
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|---|---|
| LT1111CS8PBF | 制造商:Linear Technology 功能描述:LT1111CS8PBF |
| LT1111I | 制造商:LINER 制造商全称:Linear Technology 功能描述:Micropower DC/DC Converter Adjustable and Fixed 5V, 12V |
| LT1111IS8 | 功能描述:IC REG BUCK BOOST INV ADJ 8SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT1111IS8#PBF | 功能描述:IC REG BUCK BOOST INV ADJ 8SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LT1111IS8#TR | 功能描述:IC REG BUCK BOOST INV ADJ 8SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
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