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參數(shù)資料
| 型號： | LTC3701EGN |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 2-Phase, Low Input Voltage, Dual Step-Down DC/DC Controller |
| 中文描述： | 1 A DUAL SWITCHING CONTROLLER, 890 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 0.150 INCH, PLASTIC, SSOP-16 |
| 文件頁數(shù)： | 11/20頁 |
| 文件大小： | 250K |
| 代理商： | LTC3701EGN |
11
LTC3701
3701fa
size for a fixed inductor value, but is very dependent on the
inductance selected. As inductance increases, core losses
go down. Unfortunately, increased inductance requires
more turns of wire and therefore copper losses will in-
crease. Ferrite designs have very low core losses and are
preferred at high switching frequencies, so design goals
can concentrate on copper loss and preventing saturation.
Ferrite core material saturates “hard,” which means that
inductance collapses abruptly when the peak design cur-
rent is exceeded. This results in an abrupt increase in
inductor ripple current and consequent output voltage
ripple. Do not allow the core to saturate!
Molypermalloy (from Magnetics, Inc.) is a very good, low
loss core material for toroids, but is more expensive than
ferrite. A reasonable compromise from the same manu-
facturer is Kool M
μ
. Toroids are very space efficient,
especially when several layers of wire can be used, while
inductors wound on bobbins are generally easier to sur-
face mount. However, new designs for surface mount that
do not increase the height significantly are available from
Coiltronics, Coilcraft, Dale and Sumida.
Power MOSFET Selection
An external P-channel MOSFET must be selected for use
with each channel of the LTC3701. The main selection
criteria for the power MOSFET are the threshold voltage
V
GS(TH)
, “on” resistance R
DS(ON)
, reverse transfer capaci-
tance C
RSS
and the total gate charge.
Since the LTC3701 is designed for operation down to low
input voltages, a sublogic level threshold MOSFET (R
DS(ON)
guaranteed at V
GS
= 2.5V) is required for applications that
work close to this voltage. When these MOSFETs are used,
make sure that the input supply to the LTC3701 is less than
the absolute maximum MOSFET V
GS
rating, typically 8V.
The required minimum R
DS(ON)
of the MOSFET is gov-
erned by its allowable power dissipation. For applications
that may operate the LTC3701 in dropout, i.e., 100% duty
cycle, the required R
DS(ON)
is given by:
R
P
I
p
DS ON DC
(
P
)
OUT MAX
(
)
%
)
=
=
(
+
(
)
100
2
1
δ
where P
P
is the allowable power dissipation and
δ
p is the
temperature dependency of R
DS(ON)
. (1 +
δ
p) is generally
given for a MOSFET in the form of a normalized R
DS(ON)
vs
temperature curve, but
δ
p = 0.005/
°
C can be used as an
approximation for low voltage MOSFETs.
In applications where the maximum duty cycle is less than
100% and the LTC3701 is in continuous mode, the R
DS(ON)
is governed by:
P
DC I
OUT
(
R
p
DS ON
(
P
2
1
δ
)
)
+
(
)
where DC is the maximum operating duty cycle for that
channel of the LTC3701.
Output Diode Selection
The catch diode carries load current during the switch off-
time. The average diode current is therefore dependent on
the P-channel MOSFET duty cycle. At high input voltages,
the diode conducts most of the time. As V
IN
approaches
V
OUT
, the diode conducts for only a small fraction of the
time. The most stressful condition for the diode is when
the output is short-circuited. Under this condition, the
diode must safely handle I
PEAK
at close to 100% duty
cycle. Therefore, it is important to adequately specify the
diode peak current and average power dissipation so as
not to exceed the diode’s ratings.
Under normal load conditions, the average current con-
ducted by the diode is:
I
V
V
V
V
I
D
IN
OUT
D
IN
OUT
=
+
–
The allowable forward voltage drop in the diode is calcu-
lated from the maximum short-circuit current as:
V
P
I
F
D
PEAK
≈
where P
D
is the allowable power dissipation and will be
determined by efficiency and/or thermal requirements.
A Schottky diode is a good choice for low forward drop and
fast switching time. Remember to keep lead length short
and observe proper grounding (see Board Layout Check-
list) to avoid ringing and increased dissipation.
APPLICATIOU
W
U
U
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| LTC3701EGN#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)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 |
| LTC3701EGN#TR | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 標(biāo)準(zhǔn)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) |
| LTC3701EGN#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 標(biāo)準(zhǔn)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) |
| LTC3701EGNPBF | 制造商:Linear Technology 功能描述:DC-DC Controller Dual Step-Dn 10V SSOP16 |
| LTC3701EGNTRPBF | 制造商:LINEAR TECHNOLGY 功能描述: |
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