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參數(shù)資料
| 型號： | LT1107CS8-5#TR |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1.5 A SWITCHING REGULATOR, 88 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | SOIC-8 |
| 文件頁數(shù)： | 15/16頁 |
| 文件大?。?/td> | 207K |
| 代理商： | LT1107CS8-5#TR |
8
LT1107
1107fa
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:
where R
′ = 0.65 + DCRL
VL = VIN – 0.75V
As an example, suppose –5V at 50mA is to be generated
from a 4.5V to 5.5V input. Recalling Equation (14),
Energy required from the inductor is:
Picking an inductor value of 100
H with 0.2 DCR results
in a peak switch current of:
Substituting IPEAK into Equation (04) results in:
Since 5.28
J > 3.82J, the 100H inductor will work.
With this relatively small input range, RLIM is not usually
necessary and the ILIM pin can be tied directly to VIN. As in
the step-down case, peak switch current should be limited
to ~650mA.
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.
P
f
mW
kHz
J
L
OSC
==
275
63
44
17
.( )
It
V
R
e
L
Rt
L
()=
′
′
115
()
where DC = duty cycle (0.50 in step-down mode)
VSW = switch drop in step-down mode
VD = diode drop (0.5V for a 1N5818)
IOUT = output current
VOUT = output voltage
VIN = minimum input voltage
VSW is actually a function of switch current which is in turn
a function of VIN, L, time, and VOUT. To simplify, 1.5V can
be used for VSW as a very conservative value.
Once IPEAK is known, inductor value can be derived from:
where tON = switch ON time (7s).
Next, the current limit resistor RLIM is selected to give
IPEAK from the Maximum Switch Current vs RLIM curve.
The addition of this resistor keeps maximum switch cur-
rent constant as the input voltage is increased.
As an example, suppose 5V at 300mA is to be generated
from a 12V to 24V input. Recalling Equation (10):
Next, inductor value is calculated using Equation (11):
L
mA
sH
=
=
12 1 5
5
600
764
13
.
()
Use the next lowest standard value (56
H).
Then pick RLIM from the curve. For IPEAK = 600mA, RLIM
= 56
.
Inductor Selection –– Positive-to-Negative Converter
Figure 4 shows hookup for positive-to-negative conver-
sion. All of the output power must come from the inductor.
In this case,
P
(14)
L =+
()()
VV
I
OUT
D
OUT
L
VV
V
I
t
IN MIN
SW
OUT
PEAK
ON
=
×
()
11
I
mA
PEAK =
()
+
=
2 300
050
50 5
12 15
05
600
12
.
..
()
P
= 275mW
(16 )
L =
+
()()
50 5
50
VV
mA
.
I
VV
e
mA
PEAK
s
H
=
()
+
()
=
45
075
065
0 2
1
325
18
085
9
100
..
()
.
EH
A
J
L =
()(
) =
1
2
100
0 325
5 28
19
2
..
( )
U
S
A
O
PPLICATI
WU
U
I FOR ATIO
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| LT1107IS8 | 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(biāo)準(zhǔn)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#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(biāo)準(zhǔn)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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