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參數(shù)資料
| 型號： | LTC3731HUH#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 5 A SWITCHING CONTROLLER, 750 kHz SWITCHING FREQ-MAX, PQCC32 |
| 封裝： | 5 X 5 MM, LEAD FREE, PLASTIC, MO-220WHHD, QFN-32 |
| 文件頁數(shù)： | 7/34頁 |
| 文件大小： | 427K |
| 代理商： | LTC3731HUH#PBF |
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LTC3731H
3731Hfb
applicaTions inForMaTion
BothMOSFETshaveI2RlosseswhilethetopsideN-channel
equation includes an additional term for transition losses,
which peak at the highest input voltage. For VIN < 12V,
the high current efficiency generally improves with larger
MOSFETs, while for VIN > 12V, the transition losses rapidly
increase to the point that the use of a higher RDS(ON)device
with lower CMILLERactuallyprovideshigherefficiency.The
synchronous MOSFET losses are greatest at high input
voltage when the top switch duty factor is low or during
a short circuit when the synchronous switch is on close
to 100% of the period.
The term (1 +
d ) is generally given for a MOSFET in the
form of a normalized RDS(ON) vs temperature curve, but
d = 0.005/°C can be used as an approximation for low
voltage MOSFETs.
The Schottky diodes (D1 to D3 in Figure 1) conduct during
the dead time between the conduction of the two large
power MOSFETs. This prevents the body diode of the bot-
tom MOSFET from turning on, storing charge during the
dead time and requiring a reverse recovery period which
could cost as much as several percent in efficiency. A 2A
to 8A Schottky is generally a good compromise for both
regions of operation due to the relatively small average
current. Larger diodes result in additional transition loss
due to their larger junction capacitance.
CIN and COUT Selection
In continuous mode, the source current of each top
N-channel MOSFET is a square wave of duty cycle VOUT/
VIN. A low ESR input capacitor sized for the maximum
RMS current must be used. The details of a close form
equation can be found in Application Note 77. Figure 6
showstheinputcapacitorripplecurrentfordifferentphase
configurations with the output voltage fixed and input volt-
age varied. The input ripple current is normalized against
the DC output current. The graph can be used in place of
tedious calculations. The minimum input ripple current
can be achieved when the product of phase number and
output voltage, N(VOUT), is approximately equal to the
input voltage VIN or:
V
k
N
where k
N
OUT
IN
=
= 1 2
1
, , ..., –
So the phase number can be chosen to minimize the input
capacitor size for the given input and output voltages.
In the graph of Figure 4, the local maximum input RMS
capacitor currents are reached when:
V
k
N
where k
N
OUT
IN
=
2
1
1 2
–
, , ...,
Theseworst-caseconditionsarecommonlyusedfordesign
becauseevensignificantdeviationsdonotoffermuchrelief.
Note that capacitor manufacturer’s ripple current ratings
are often based on only 2000 hours of life. This makes
it advisable to further derate the capacitor or to choose
a capacitor rated at a higher temperature than required.
Several capacitors may also be paralleled to meet size or
height requirements in the design. Always consult the
capacitor manufacturer if there is any question.
The Figure 6 graph shows that the peak RMS input current
is reduced linearly, inversely proportional to the number N
of stages used. It is important to note that the efficiency
loss is proportional to the input RMS current squared and
therefore a 3-stage implementation results in 90% less
power loss when compared to a single phase design. Bat-
tery/input protection fuse resistance (if used), PC board
trace and connector resistance losses are also reduced
by the reduction of the input ripple current in a PolyPhase
system.Therequiredamountofinputcapacitanceisfurther
DUTY FACTOR (VOUT/VIN)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
0.6
0.5
0.4
0.3
0.2
0.1
0
3731H F06
RMS
INPUT
RIPPLE
CURRENT
DC
LOAD
CURRENT
6-PHASE
4-PHASE
12-PHASE
3-PHASE
2-PHASE
1-PHASE
Figure 6. Normalized Input RMS Ripple Current
vs Duty Factor for One to Six Output Stages
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LTC3731IG | 制造商:Linear Technology 功能描述:LDO Cntrlr SYNC BUCK REG 0.6V to 6V 36-Pin SSOP |
| LTC3731IG#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 36-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 |
| LTC3731IG#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 36-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 |
| LTC3731IUH | 制造商:Linear Technology 功能描述:LDO Cntrlr SYNC BUCK REG 0.6V to 6V 32-Pin QFN EP |
| LTC3731IUH#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 32-QFN 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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