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| 型号： | LT1108CS8-5#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/12页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BST INV 5V .4A 8SOIC |
| 标准包装： | 2,500 |
| 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： | 19kHz |
| 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： | 带卷 (TR) |
| 供应商设备封装： | 8-SOIC |
LT1108
A PPLICATI
S I FOR ATIO
provided by the PNP transistor, supplies proper polarity
feedback information to the regulator.
V IN
Another situation where the I LIM feature is useful occurs
when the device goes into continuous mode operation. This
occurs in step-up mode when
R3
I LIM
V IN
SW1
V OUT + V DIODE
V IN ? V SW
<
1
1 ? DC
.
( 25 )
+
FB
C2
LT1108
SW2
L1
When the input and output voltages satisfy this relation-
ship, inductor current does not go to zero during the switch-
GND
D1
1N5818
+
C1
R1
R2
–V OUT
LT1108 ? F04
OFF time. When the switch turns on again, the current ramp
starts from the non-zero current level in the inductor just
prior to switch turn-on. As shown in Figure 6, the inductor
current increases to a high level before the comparator
Figure 4. Positive-to-Negative Converter
turns off the oscillator. This high current can cause exces-
sive output ripple and requires oversizing the output ca-
L1
D1
+
C1
R1
V OUT
pacitor and inductor. With the I LIM feature, however, the
switch current turns off at a programmed level as shown in
Figure 7, keeping output ripple to a minimum.
I LIM
V IN
2N3906
+
C2
LT1108
SW1
( )
V OUT = 1.245V + 0.6V
AO
GND
FB
SW2
R2
R1
R2
I L
–V IN
LT1108 ? F05
Figure 5. Negative-to-Positive Converter
USING THE I LIM PIN
The LT1108 switch can be programmed to turn off at a set
switch current, a feature not found on competing devices.
SWITCH
ON
OFF
Figure 6. No Current Limit Causes Large Inductor
Current Build-Up
LT1108 ? F06
This enables the input to vary over a wide range without
exceeding the maximum switch rating or saturating the
inductor. Consider the case where analysis shows the
LT1108 must operate at an 800mA peak switch current with
I L
PROGRAMMED CURRENT LIMIT
a 2.0V input. If V IN rises to 4V, the peak switch current will
rise to 1.6A, exceeding the maximum switch current rating.
SWITCH
ON
OFF
With the proper resistor selected (see the “Maximum
Switch Current vs R LIM ” characteristic), the switch current
will be limited to 800mA, even if the input voltage increases.
10
LT1108 ? F07
Figure 7. Current Limit Keeps Inductor Current Under Control
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1108CS8PBF | 制造商:Linear Technology 功能描述:DC/DC Converter Adj Micropower 2-30V SO8 |
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