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| 型号： | LT1108CN8-12 |
| 厂商： | Linear Technology |
| 文件页数： | 8/12页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BST INV 12V .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： | 12V |
| 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： | 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 |
LT1108
A PPLICATI
S I FOR ATIO
In this mode the switch is arranged in common collector or
step-down mode. The switch drop can be modeled as a
0.75V source in series with a 0.65 ? resistor. When the
switch closes, current in the inductor builds according to
The usual step-up configuration for the LT1108 is shown in
Figure 1. The LT1108 first pulls SW1 low causing V IN –
V CESAT to appear across L1. A current then builds up in L1.
At the end of the switch-ON time the current in L1 is
?
1 – e L ?
t
I L () =
V L
R '
?
?
–R't ?
?
( 15 )
I PEAK =
V IN
L
t ON *
( 20 )
where: R' = 0.65 ? + DCR L
V L = V IN – 0.75V
As an example, suppose – 5V at 100mA is to be generated
from a 4.5V to 5.5V input. Recalling Equation (14),
V IN
R3
I LIM
V IN
SW1
L1
D1
R2
+
V OUT
P L = ( ? – 5V ? + 0.5V )( 100mA ) = 550mW.
(16)
LT1108
FB
C1
Energy required from the inductor is
GND
SW2
R1
= = 28 . 9 μ J
P L
f OSC
550mW
19 kHz
( 17 )
Figure 1. Step-Up Mode Hookup
LT1108 ? F01
Picking an inductor value of 220 μ H with 0.3 ? DCR results
in a peak switch current of
Immediately after switch turn-off, the SW1 voltage pin
starts to rise because current cannot instantaneously stop
( ) V ? 1 – e – 0 . 95 ? × 36 μ s ?
( 0 . 65 ? + 0 . 3 ? ) ? ?
4 . 5 V – 0 . 75
I PEAK = 220 μ H ?
= 568 mA
?
(18)
flowing in L1. When the voltage reaches V OUT + V D , the
inductor current flows through D1 into C1, increasing V OUT .
This action is repeated as needed by the LT1108 to keep V FB
at the internal reference voltage of 1.245V. R1 and R2 set
the output voltage according to the formula
( )( )
220 μ H 0 . 568 A 2 = 35 . 5 μ J
E L =
(
)
V OUT = ? 1 +
?
R 1 ?
Substituting I PEAK into Equation (04) results in
1
2
( 19 )
? R 2 ?
? 1 . 245 V
STEP-DOWN (BUCK MODE) OPERATION
( 21 )
Since 35.5 μ J > 28.9 μ J, the 220 μ H inductor will work.
Finally, R LIM should be selected by looking at the Switch
Current vs R LIM curve. In this example, R LIM = 150 ? .
STEP-UP (BOOST MODE) OPERATION
A step-up DC/DC converter delivers an output voltage
higher than the input voltage. Step-up converters are not
short-circuit protected since there is a DC path from input
to output.
8
A step-down DC/DC converter converts a higher voltage to
a lower voltage. The usual hookup for an LT1108 based
step-down converter is shown in Figure 2.
When the switch turns on, SW2 pulls up to V IN – V SW . This
puts a voltage across L1 equal to V IN – V SW – V OUT , causing
a current to build up in L1. At the end of the switch- ON time,
the current in L1 is equal to
*Expression 20 neglects the effect of switch and coil resistance. This is taken into account in the
"Inductor Selection" section.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1108CN8-12#PBF | 功能描述:IC REG BUCK BST INV 12V .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:20 系列:SIMPLE SWITCHER® 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:12V 输入电压:4 V ~ 60 V PWM 型:电压模式 频率 - 开关:52kHz 电流 - 输出:1A 同步整流器:无 工作温度:-40°C ~ 125°C 安装类型:通孔 封装/外壳:16-DIP（0.300"，7.62mm） 包装:管件 供应商设备封装:16-DIP 其它名称:*LM2575HVN-12LM2575HVN-12 |
| LT1108CN8-5 | 功能描述:IC REG BUCK BST INV 5V 0.4A 8DIP 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 |
| LT1108CN8-5#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: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 |
| LT1108CS8 | 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 |
| LT1108CS8#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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