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| 型号： | LTC3811EUHF#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 30/48页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 38-QFN |
| 标准包装： | 2,500 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 850kHz |
| 占空比： | 90% |
| 电源电压： | 4.5 V ~ 30 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 38-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
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LTC3811
APPLICATIONS INFORMATION
C IN and C OUT Selection
In continuous mode, the drain current of each top N-channel
0.6
0.5
MOSFET is a square wave of duty cycle V OUT /V IN . 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 17 shows the input capacitor
ripple current for different phase con?gurations with the
output voltage ?xed and input voltage varied. The input
ripple current is normalized against the DC output current.
0.4
0.3
0.2
0.1
1-PHASE
2-PHASE
3-PHASE
4-PHASE
6-PHASE
The graph can be used in place of tedious calculations. The
minimum input ripple current can be achieved when the
0
0.1
0.2
0.3 0.4 0.5 0.6 0.7
DUTY FACTOR (V OUT /V IN )
0.8
0.9
V OUT k
V IN
productofphasenumberandoutputvoltage,N(V OUT ),is
approximately equal to the input voltage V IN or:
= where k = 1, 2, ..., N – 1
N
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 17, the local maximum input RMS
capacitor currents are reached when:
3811 F17
Figure 17. Normilized Input RMS Ripple Current vs
Duty Factor for 1 to 6 Output Stages
system. The required amount of input capacitance is further
reduced by the factor, N, due to the effective increase in
the frequency of the current pulses.
The selection of C OUT is driven by the required effective
series resistance (ESR). Typically once the ESR require-
ment has been met, the RMS current rating generally far
V OUT
V IN
=
2k ? 1
2 N
where k = 1, 2, ..., N
exceeds the I RIPPLE(P-P) requirements. The steady-state
output ripple ( Δ V OUT ) is determined by:
8NfC OUT ?
Theseworst-caseconditionsarecommonlyusedfordesign
because even signi?cant deviations do not offer much relief.
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 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 ef?ciency
loss is proportional to the input RMS current squared and
therefore a 2-stage implementation results in 75% 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
? 1 ?
Δ V OUT ≈ Δ I RIPPLE ? ESR + ?
?
where f = operating frequency of each stage, N is the
number of phases, C OUT = output capacitance and
Δ I RIPPLE = combined inductor ripple currents.
The output ripple varies with input voltage since Δ I L is a
function of input voltage. The output ripple will be less than
50mV at max V IN with Δ I L = 0.4I OUT(MAX) /N assuming:
C OUT required ESR < 2N(R SENSE ) and
C OUT > 1/(8Nf)(R SENSE )
The emergence of very low ESR ceramic capacitors in
small, surface mount packages makes very physically
small implementations possible. The ability to externally
compensate the switching regulator loop using the
LTC3811’s true operational error ampli?er allows a much
wider selection of output capacitor types. The ability to
3811f
30
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| LTC3812EFE5#PBF | 制造商:Linear Technology 功能描述: |
| LTC3812EFE-5#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
| LTC3812EFE-5#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3812IFE-5#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3812IFE-5#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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