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參數(shù)資料
| 型號(hào)： | LT1108CN8 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Micropower DC/DC Converter Adjustable and Fixed 5V, 12V |
| 中文描述： | 1.5 A SWITCHING REGULATOR, 19 kHz SWITCHING FREQ-MAX, PDIP8 |
| 封裝： | PLASTIC, DIP-8 |
| 文件頁(yè)數(shù)： | 8/12頁(yè) |
| 文件大小： | 266K |
| 代理商： | LT1108CN8 |
8
LT1108
U
S
A
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
O
PPLICATI
IU
U
I
t
V
R
e
L
L
'
L
( )
=
–
(
)
–Rt
1
15
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),
P
L
=
(
–5V
+ 0.5V
)(
100mA
)
= 550mW.
(16)
Energy required from the inductor is
P
f
OSC
mW
kHz
J
L
=
=
550
19
28 9
17
(
.
)
μ
Picking an inductor value of 220
μ
H with 0.3
DCR results
in a peak switch current of
I
V
V
e
mA
PEAK
s
H
=
(
)
+
(
568
)
=
×
μ
4 5
.
–0 75
65
0 3
.
1
–0 95
36
220
.
–
0
μ
Substituting I
PEAK
into Equation (04) results in
E
H
A
J
L
=
(
)(
)
=
1
2
220
0 568
.
35 5
19
(
2
μ
μ
.
)
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.
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
I
V
L
t
PEAK
IN
ON
=
*
(
)
20
(18)
*Expression 20 neglects the effect of switch and coil resistance. This is taken into account in the
"Inductor Selection" section.
Immediately after switch turn-off, the SW1 voltage pin
starts to rise because current cannot instantaneously stop
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
V
R
R
V
OUT
=
+
(
)
1
2
1
1 245
.
21
( )
STEP-DOWN (BUCK MODE) OPERATION
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
Figure 1. Step-Up Mode Hookup
L1
LT1108 F01
GND
SW2
SW1
LIM
I
IN
V
D1
R3
LT1108
+
V
OUT
R2
R1
C1
V
IN
FB
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|---|---|
| LT1108CN8#PBF | 功能描述:IC REG BUCK BST INV ADJ .4A 8DIP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:250 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V 輸入電壓:2.05 V ~ 6 V PWM 型:電壓模式 頻率 - 開關(guān):2MHz 電流 - 輸出:500mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:6-UFDFN 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:6-SON（1.45x1） 產(chǎn)品目錄頁(yè)面:1032 (CN2011-ZH PDF) 其它名稱:296-25628-2 |
| LT1108CN8-12 | 功能描述:IC REG BUCK BST INV 12V .4A 8DIP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類型:升壓（升壓） 輸出類型:可調(diào)式 輸出數(shù):1 輸出電壓:1.24 V ~ 30 V 輸入電壓:1.5 V ~ 12 V PWM 型:電流模式，混合 頻率 - 開關(guān):600kHz 電流 - 輸出:500mA 同步整流器:無(wú) 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:8-SOIC |
| LT1108CN8-12#PBF | 功能描述:IC REG BUCK BST INV 12V .4A 8DIP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:20 系列:SIMPLE SWITCHER® 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:12V 輸入電壓:4 V ~ 60 V PWM 型:電壓模式 頻率 - 開關(guān):52kHz 電流 - 輸出:1A 同步整流器:無(wú) 工作溫度:-40°C ~ 125°C 安裝類型:通孔 封裝/外殼:16-DIP（0.300"，7.62mm） 包裝:管件 供應(yīng)商設(shè)備封裝:16-DIP 其它名稱:*LM2575HVN-12LM2575HVN-12 |
| LT1108CN8-5 | 功能描述:IC REG BUCK BST INV 5V 0.4A 8DIP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類型:升壓（升壓） 輸出類型:可調(diào)式 輸出數(shù):1 輸出電壓:1.24 V ~ 30 V 輸入電壓:1.5 V ~ 12 V PWM 型:電流模式，混合 頻率 - 開關(guān):600kHz 電流 - 輸出:500mA 同步整流器:無(wú) 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:8-SOIC |
| LT1108CN8-5#PBF | 功能描述:IC REG BUCK BST INV 5V 0.4A 8DIP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類型:升壓（升壓） 輸出類型:可調(diào)式 輸出數(shù):1 輸出電壓:1.24 V ~ 30 V 輸入電壓:1.5 V ~ 12 V PWM 型:電流模式，混合 頻率 - 開關(guān):600kHz 電流 - 輸出:500mA 同步整流器:無(wú) 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:8-SOIC |
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