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參數(shù)資料
| 型號： | LTC1649CS |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Low Power Timer 8-SOIC -40 to 85 |
| 中文描述： | 20 A SWITCHING CONTROLLER, 260 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 0.150 INCH, PLASTIC, SO-16 |
| 文件頁數(shù)： | 8/16頁 |
| 文件大小： | 201K |
| 代理商： | LTC1649CS |
8
LTC1649
EXTERNAL COMPONENT SELECTION
Power MOSFETs
Two N-channel power MOSFETs are required for most
LTC1649 circuits. These should be selected primarily by
on-resistance considerations; thermal dissipation is often
a secondary concern in high efficiency designs. The
LTC1649 is designed to be used with 5V logic-level MOS-
FETs; “standard” threshold MOSFETs with R
DS(ON)
speci-
fied at 10V only will not provide satisfactory performance.
MOSFET R
DS(ON)
should be chosen based on input and
output voltage, allowable power dissipation and maxi-
mum required output current. In a typical LTC1649 buck
converter circuit operating in continuous mode, the aver-
age inductor current is equal to the output load current.
This current is always flowing through either Q1 or Q2 with
the power dissipation split up according to the duty cycle:
DC (Q1) =V
OUT
V
IN
DC (Q2) = 1 –V
OUT
V
IN
=(V
IN
– V
OUT
)
V
IN
The R
ON
required for a given conduction loss can now be
calculated by rearranging the relation P = I
2
R:
R
DS(ON)
(Q1) =
=
P
MAX
(Q1)
DC(Q1)(I
MAX
2
)
V
IN
(P
MAX
)(Q1)
V
OUT
(I
MAX
2
)
R
DS(ON)
(Q2) =
=
P
MAX
(Q2)
DC(Q2)(I
MAX
2
)
V
IN
(P
MAX
)(Q2)
(V
IN
– V
OUT
)(I
MAX
2
)
P
MAX
should be calculated based primarily on required
efficiency. A typical high efficiency circuit designed for
3.3V in, 2.5V at 10A out might require no more than 3%
efficiency loss at full load for each MOSFET. Assuming
roughly 90% efficiency at this current level, this gives a
P
MAX
value of (2.5V)(10A/0.9)(0.03) = 833mW per FET
and a required R
DSON
of:
R
DS(ON)
(Q1) =
= 0.011
(3.3V)(833mW)
(2.5V)(10A
2
)
(3.3V)(833mW)
(3.3V – 2.5V)(10A
2
)
R
DS(ON)
(Q2) =
= 0.034
Note that while the required R
DS(ON)
values suggest large
MOSFETs, the dissipation numbers are less than a watt per
device—large TO-220 packages and heat sinks are not
necessarily required in high efficiency applications. Siliconix
Si4410DY and International Rectifier IRF7801 are two
small, surface mount devices with R
ON
values of 0.03
or
below with 5V of gate drive; both work well in LTC1649
circuits. A higher P
MAX
value will generally decrease
MOSFET cost and circuit efficiency and increase MOSFET
heat sink requirements.
Inductor
The inductor is often the largest component in an LTC1649
design and should be chosen carefully. Inductor value and
type should be chosen based on output slew rate require-
ments and expected peak current. Inductor value is prima-
rily controlled by the required current slew rate. The
maximum rate of rise of the current in the inductor is set
by its value, the input-to-output voltage differential and the
maximum duty cycle of the LTC1649. In a typical 3.3V to
2.5V application, the maximum rise time will be:
93%
=
(V
IN
– V
OUT
)
L
AMPS
SECOND
0.744A
μ
s
I
L
where L is the inductor value in
μ
H. A 2
μ
H inductor would
have a 0.37A/
μ
s rise time in this application, resulting in a
14
μ
s delay in responding to a 5A load current step. During
this 14
μ
s, the difference between the inductor current and
the output current must be made up by the output capaci-
tor, causing a temporary droop at the output. To minimize
this effect, the inductor value should usually be in the 1
μ
H
to 5
μ
H range for most typical 3.3V to 2.xV LTC1649
circuits. Different combinations of input and output volt-
APPLICATIO
S I
N
FOR
ATIO
U
W
U
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| LTC1649CS#PBF | 功能描述:IC REG CTRLR BUCK PWM VM 16-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標準包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產(chǎn)品目錄頁面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR |
| LTC1649CS#TR | 功能描述:IC REG CTRLR BUCK PWM VM 16-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC1649CS#TRPBF | 功能描述:IC REG CTRLR BUCK PWM VM 16-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC1649IS | 功能描述:IC REG CTRLR BUCK PWM VM 16-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
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