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| 型号： | LT1173CN8-5 |
| 厂商： | Linear Technology |
| 文件页数： | 7/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BST INV 5V 0.4A 8DIP |
| 标准包装： | 50 |
| 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： | 23kHz |
| 电流 - 输出： | 400mA |
| 同步整流器： | 无 |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 通孔 |
| 封装/外壳： | 8-DIP（0.300"，7.62mm） |
| 包装： | 管件 |
| 供应商设备封装： | 8-PDIP |
LT1173
A PPLICATI
S I FOR ATIO
As an example, suppose 9V at 50mA is to be generated
from a 3V input. Recalling Equation 02,
In the negative-to-positive case, the switch saturates and
the 0.8 ? switch ON resistance value given for Equation 04
P L = (9V + 0.5V – 3V) (50mA) = 325mW.
Energy required from the inductor is
(07)
can be used. In both cases inductor design proceeds from
Equation 03.
The step-down case is different than the preceeding three
( )
P L
F OSC
=
325mW
24 kHz
= 13 . 5 μ J .
08
in that the inductor current flows through the load in a
step-down topology (Figure 6). Current through the switch
should be limited to ~650mA in step-down mode. This can
Picking an inductor value of 100 μ H with 0.2 ? DCR results
be accomplished by using the I LIM pin. With input voltages
i PEAK = ? 1 – e 100 μ H ? = 616 m A .
in a peak switch current of
3 V ? –1 ? ? 23 μ s ?
1 ? ? ?
Substituting i PEAK into Equation 04 results in
( 09 )
in the range of 12V to 25V, a 5V output at 300mA can be
generated with a 220 μ H inductor and 100 ? resistor in
series with the I LIM pin. With a 20V to 30V input range, a
470 μ H inductor should be used along with the 100 ?
resistor.
Capacitor Selection
)
( )
E L =
1
2
( 100 μ H )( 0 . 616 A
2
= 19 . 0 μ J .
10
Selecting the right output capacitor is almost as important
as selecting the right inductor. A poor choice for a filter
Since 19 μ J > 13.5 μ J the 100 μ H inductor will work. This
trial-and-error approach can be used to select the opti-
mum inductor. Keep in mind the switch current maximum
rating of 1.5A. If the calculated peak current exceeds this,
consider using the LT1073. The 70% duty cycle of the
LT1073 allows more energy per cycle to be stored in the
inductor, resulting in more output power.
An inductor’s energy storage capability is proportional to
its physical size. If the size of the inductor is too large for
a particular application, considerable size reduction is
possible by using the LT1111. This device is pin compat-
ible with the LT1173 but has a 72kHz oscillator, thereby
reducing inductor and capacitor size requirements by a
factor of three.
For both positive-to-negative (Figure 7) and negative-to-
positive configurations (Figure 8), all the output power
must be generated by the inductor. In these cases
P L = ( ? V OUT ? + V D ) (I OUT ). (11)
In the positive-to-negative case, switch drop can be mod-
eled as a 0.75V voltage source in series with a 0.65 ?
resistor so that
capacitor can result in poor efficiency and/or high output
ripple. Ordinary aluminum electrolytics, while inexpensive
and readily available, may have unacceptably poor equiva-
lent series resistance (ESR) and ESL (inductance). There
are low-ESR aluminum capacitors on the market specifi-
cally designed for switch mode DC-DC converters which
work much better than general-purpose units. Tantalum
capacitors provide still better performance at more ex-
pense. We recommend OS-CON capacitors from Sanyo
Corporation (San Diego, CA). These units are physically
quite small and have extremely low ESR. To illustrate,
Figures 2, 3, and 4 show the output voltage of an LT1173
based converter with three 100 μ F capacitors. The peak
switch current is 500mA in all cases. Figure 2 shows a
Sprague 501D, 25V aluminum capacitor. V OUT jumps by
over 120mV when the switch turns off, followed by a drop
in voltage as the inductor dumps into the capacitor. This
works out to be an ESR of over 240m ? . Figure 3 shows the
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 70m ? .
Figure 4 shows the circuit with a 16V OS-CON unit. ESR is
now only 20m ? .
V L = V IN – 0.75V – I L (0.65 ? ).
(12)
7
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1173CN8-5#PBF | 功能描述:IC REG BUCK BST INV 5V 0.4A 8DIP 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 |
| LT1173CN8-5PBF | 制造商:Linear Technology 功能描述:LT1173CN8-5PBF |
| LT1173CN8PBF | 制造商:Linear Technology 功能描述:LT1173CN8PBF |
| LT1173CS8 | 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:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LT1173CS8#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 |
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