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參數(shù)資料
| 型號： | LTC3785EUF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PQCC24 |
| 封裝： | 4 X 4 MM, PLASTIC, MO-220WGGD, QFN-24 |
| 文件頁數(shù)： | 5/20頁 |
| 文件大?。?/td> | 275K |
| 代理商： | LTC3785EUF |
LTC3785
3785fc
applicaTions inForMaTion
eters for the power MOSFETs are the breakdown voltage
VBR(DSS),thresholdvoltageVGS(TH),on-resistanceRDS(ON),
reverse transfer capacitance CRSS and maximum current
IDS(MAX). The drive voltage is set by the 4.5V VCC supply.
Consequently,logic-levelthresholdMOSFETsmustbeused
in LTC3785 applications. If the input voltage is expected to
drop below 5V, then sub-logic threshold MOSFETs should
be considered. In order to select the power MOSFETs, the
power dissipated by the device must be known.
For switch A, the maximum power dissipation happens
in boost mode, when it remains on all the time. Its maxi-
mum power dissipation at maximum output current is
given by:
PA(BOOST)
=
VOUT
VIN
IOUT(MAX)
2
ρT RDS(ON)
where
ρT is a normalization factor (unity at 25°C) ac-
counting for the significant variation in on-resistance with
temperature,typicallyabout0.4%/°CasshowninFigure 4.
For a maximum junction temperature of 125°C, using a
value
ρT = 1.5 is reasonable.
Switch B operates in buck mode as the synchronous
rectifier. Its power dissipation at maximum output current
is given by:
PB(BUCK)
=
VIN – VOUT
VIN
IOUT(MAX)
2 ρT RDS(ON)
Switch C operates in boost mode as the control switch. Its
power dissipation at maximum current is given by:
PC(BOOST)
=
VOUT – VIN
(
)VOUT
VIN
2
IOUT(MAX)
2 ρT
RDS(ON) +k VOUT
3
IOUT(MAX)
VIN
CRSS f
whereCRSSisusuallyspecifiedbytheMOSFETmanufactur-
ers. The constant k, which accounts for the loss caused by
reverse recovery current, is inversely proportional to the
gate drive current and has an empirical value of 1.0.
For switch D, the maximum power dissipation happens in
boost mode when its duty cycle is higher than 50%. Its
maximum power dissipation at maximum output current
is given by:
PD BOOST
(
)= VOUT
VIN
IOUT(MAX)
2 ρT RDS(ON)
Typically, switch A has the highest power dissipation and
switch B has the lowest power dissipation unless a short
occurs at the output. From a known power dissipated
in the power MOSFET, its junction temperature can be
obtained using the following formula:
TJ = TA + P RTH(JA)
The RTH(JA) to be used in the equation normally includes
the RTH(JC) for the device plus the thermal resistance from
the case to the ambient temperature (RTH(CA)). This value
of TJ can then be compared to the original, assumed value
used in the iterative calculation process.
SCHOTTKY DIODE (D1, D2) SELECTION
Optional Schottky diodes D1 and D2 shown in the Block
Diagramconductduringthedeadtimebetweentheconduc-
tion of the power MOSFET switches. They are intended to
prevent the body diode of synchronous switches B and D
from turning on and storing charge during the dead time.
In particular, D2 significantly reduces reverse recovery
current between switch D turn off and switch C turn on,
which improves converter efficiency and reduces switch C
voltage stress. In order for D2 to be effective, it must be
located in very close proximity to SWD.
Figure 4. Normalized RDS(ON) vs Temperature
JUNCTION TEMPERATURE (°C)
–50
ρ
TNORMALIZED
ON-RESIST
ANCE
1.0
1.5
150
3785 F04
0.5
0
50
100
2.0
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| LTC3785EUF#PBF | 功能描述:IC REG CTRLR BST PWM VM 24-QFN 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(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 |
| LTC3785EUF#TRPBF | 功能描述:IC REG CTRLR BST PWM VM 24-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 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) |
| LTC3785EUF-1#PBF | 功能描述:IC REG CTRLR BST PWM VM 24-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 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) |
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| LTC3785EUFPBF | 制造商:Linear Technology 功能描述:10V Synch Buck-Boost Controller LTC3785 |
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