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參數(shù)資料
| 型號： | LT1578CS8-2.5 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | CAP 10UF 63V ELECT TG SMD |
| 中文描述： | SWITCHING REGULATOR, 240 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | 0.150 INCH, PLASTIC, SO-8 |
| 文件頁數(shù)： | 25/28頁 |
| 文件大?。?/td> | 286K |
| 代理商： | LT1578CS8-2.5 |
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25
LT1578/LT1578-2.5
APPLICATIO
S I
FOR
ATIO
U
inductor is therefore typically based on ensuring that peak
switch current rating is not exceeded. This gives the
lowest value of inductance that can be used, but in some
cases (lower output load currents) it may give a value that
creates unnecessarily high output ripple voltage. A com-
promise value is often chosen that reduces output ripple.
As you can see from the graph, largeinductors will not
give arbitrarily low ripple, but smallinductors can give
high ripple.
The difficulty in calculating the minimum inductor size
needed is that you must first know whether the switcher
will be in continuous or discontinuous mode at the critical
point where switch current is 1.5A. The first step is to use
the following formula to calculate the load current where
the switcher must use continuous mode. If your load
current is less than this, use the discontinuous mode
formula to calculate the minimum inductor value needed.
If the load current is higher, use the continuous mode
formula.
Output current where continuous mode is needed:
W
U
U
For the example above, with maximum load current of
0.25A:
I
A
CONT
=
( ) ( )
)
(
+ +
(
)
=
4 5 5 5 5 5 5 0 5
.
0 38
2
2
.
.
This says that discontinuous mode can be used and the
minimum inductor needed is found from:
( )(
L
H
MIN
=
)
( )
=
2 5 0 25
200 10
1 5
.
5 6
3
2
.
In practice, the inductor should be increased by about 30%
over the calculated minimum to handle losses and varia-
tions in value. This suggests a minimum inductor of 7.3
μ
H
for this application, but looking at the ripple voltage chart
shows that output ripple voltage could be reduced by a fac-
tor of two by using a 30
μ
H inductor. There is no rule of thumb
here to make a final decision. If modest ripple is needed and
the larger inductor does the trick, this is probably the best
solution. If ripple is noncritical use the smaller inductor. If
ripple is extremely critical, a second stage filter may have
to be added in any case, and the lower value of inductance
can be used. Keep in mind that the output capacitor is the
other critical factor in determining output ripple voltage.
Ripple shown on the graph (Figure 16) is with a capacitor’s
ESR of 0.1
. This is
reasonable for AVX type TPS “D” or
“E” size surface mount solid tantalum capacitors, but the
final capacitor chosen must be looked at carefully for ESR
characteristics.
I
V
I
V
V
V
V
V
CONT
IN
)
IN
OUT
IN
OUT
F
=
( ) ( )
(
+
(
+
+
)
2
2
4
Minimum inductor discontinuous mode:
=
(
( )( )
L
V
I
f I
MIN
OUT
OUT
2
P
)(
)
2
Minimum inductor continuous mode:
L
V
V
f V
( )
V
I
I
V
V
V
MIN
IN
OUT
IN
OUT
P
OUT
OUT
F
IN
=
( )(
)
+
(
)
+
+
(
)
2
1
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| LT1578IS8 | 功能描述:IC REG BUCK ADJ 1.5A 8SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:2,500 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，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開關:- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應商設備封裝:10-MSOP 裸露焊盤 |
| LT1578IS8#PBF | 功能描述:IC REG BUCK ADJ 1.5A 8SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:2,500 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，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開關:- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應商設備封裝:10-MSOP 裸露焊盤 |
| LT1578IS8#TR | 功能描述:IC REG BUCK ADJ 1.5A 8SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:2,500 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，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開關:- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應商設備封裝:10-MSOP 裸露焊盤 |
| LT1578IS8#TRPBF | 功能描述:IC REG BUCK ADJ 1.5A 8SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:2,500 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，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開關:- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應商設備封裝:10-MSOP 裸露焊盤 |
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