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參數(shù)資料
| 型號： | LT1107IS8 |
| 英文描述： | DC to DC Converter |
| 中文描述： | DC至DC轉(zhuǎn)換器 |
| 文件頁數(shù)： | 7/16頁 |
| 文件大?。?/td> | 206K |
| 代理商： | LT1107IS8 |
7
LT1107
1107fa
Inductor Selection –– Step-Up Converter
In a step-up, or boost converter (Figure 1), power gener-
ated by the inductor makes up the difference between
input and output. Power required from the inductor is
determined by:
where V
D
is the diode drop (0.5V for a 1N5818 Schottky).
Energy required by the inductor per cycle must be equal or
greater than:
P
f
L
OSC
/
in order for the converter to regulate the output.
When the switch is closed, current in the inductor builds
according to:
where R
′
is the sum of the switch equivalent resistance
(0.8
typical at 25
°
C) and the inductor DC resistance.
When the drop across the switch is small compared to V
IN
,
the simple lossless equation:
V
L
can be used. These equations assume that at t = 0,
inductor current is zero. This situation is called “discon-
tinuous mode operation” in switching regulator parlance.
Setting “t” to the switch ON time from the LT1107 speci-
fication table (typically 11
μ
s) will yield I
PEAK
for a specific
“L” and V
IN
. Once I
PEAK
is known, energy in the inductor
at the end of the switch ON time can be calculated as:
=
1
2
As an example, suppose 12V at 60mA is to be generated
from a 3V to 6V input. Recalling equation (1),
(
Energy required from the inductor is:
Picking an inductor value of 33
μ
H with 0.2
DCR results
in a peak switch current of:
1
Substituting I
PEAK
into Equation 4 results in:
L
=
(
2
Since 11.9
μ
J > 9.05
μ
J, the 33
μ
H inductor will work. This
trial-and-error approach can be used to select the opti-
mum inductor.
A resistor can be added in series with the I
LIM
pin to invoke
switch current limit. The resistor should be picked so the
calculated I
PEAK
at minimum V
IN
is equal to the Maximum
Switch Current (from Typical Performance Characteristic
curves). Then, as V
IN
increases, peak switch current is
held constant, resulting in increasing efficiency.
Inductor Selection –– Step-Down Converter
The step-down case (Figure 2) differs from the step-up in
that the inductor current flows through the load during
both the charge and discharge periods of the inductor.
Current through the switch should be limited to ~650mA
in this mode. Higher current can be obtained by using an
external switch (see LT1111 and LT1110 data sheets). The
I
LIM
pin is the key to successful operation over varying
inputs.
After establishing output voltage, output current and input
voltage range, peak switch current can be calculated by the
formula:
I
DC
V
V
IN
SW
U
S
A
O
PPLICATI
IU
U
( )
I
t
V
R
e
L
IN
′
L
()
( )
3
=
′
1
I
t
t
L
IN
( )
=
( )
E
L
must be greater than P
L
/f
OSC
for the converter to deliver
the required power. For best efficiency I
PEAK
should be
kept to 1A or less. Higher switch currents will cause
excessive drop across the switch resulting in reduced
efficiency. In general, switch current should be held to as
low a value as possible in order to keep switch, diode and
inductor losses at a minimum.
P
f
mW
kHz
J
L
OSC
=
=
570
63
9 05
.
7
( )
μ
E
H
A
J
)(
)
=
1
33
0 85
.
11 91
.
9
( )
2
μ
μ
E
LI
L
PEAK
5
( )
2
P
V
V
V
mA
mW
L
=
+
)(
)
=
12
0 5
.
3
60
570
6
( )
I
V
e
mA
PEAK
s
H
=
3
1
850
8
( )
1
11
μ
33
μ
P
V
V
V
I
L
OUT
D
IN MIN
OUT
=
+
(
)
)
()
I
V
V
+
V
PEAK
OUT
OUT
D
D
=
+
2
10
( )
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| LT1107IS8#PBF | 功能描述:IC REG BUCK BOOST INV ADJ 8SOIC 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(guān):- 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(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤 |
| LT1107IS8#TR | 功能描述:IC REG BUCK BOOST INV ADJ 8SOIC 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(guān):- 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(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤 |
| LT1107IS8#TRPBF | 功能描述:IC REG BUCK BOOST INV ADJ 8SOIC 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(guān):- 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(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤 |
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