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| 型号： | LTC3811EUHF#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 23/48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
Duty Cycle Considerations
COMP
The duty cycle for a buck converter is well known:
LTC3811
D = = t ON ? f
V OUT
V IN
FB
R1
R2
V OUT
C OUT
Rearranging, the minimum on-time for a given application
can be calculated:
SGND
3811 F09
t ON ( MIN ) =
V OUT
V IN ( MAX ) ? f
DIVIDER AND COMPENSATION
COMPONENTS PLACED NEAR
FB, SGND AND COMP PINS
Figure 9. Output Divider and Compensation
V OUT = 0.6V ? ? 1 +
Foragiveninputandoutputvoltage,itisimportanttoknow
how close the minimum on-time of the application comes
to the minimum on-time of the control IC. The LTC3811
has a typical minimum on-time of 65ns, allowing both high
input to output ratios and high frequency operation.
In an application circuit, if the IC’s minimum on-time
exceeds the value required in the duty cycle equations,
the converter will begin to skip pulses and operate at a
fraction of the intended frequency. This frequency division
will result in higher current and voltage ripple and is of
particular concern in forced continuous applications with
low ripple currents at light loads.
Setting the Output Voltage
The LTC3811 output voltages are each set by external
feedback resistor dividers, according to the following
equation:
? R2 ?
?
? R1 ?
Care should be taken to place the output divider resistors
and the compensation components as close as possible
to the IC FB and SGND pins, in order to prevent switching
noise from coupling into the signal path . This con?guration
is shown in Figure 9. The top of R2 is normally routed to
the top of the output capacitor, or to the output of the dif-
ferential ampli?er, if remote sensing is being employed.
Because the common mode range of the current compara-
tor input stages is 0V to 3.5V, the output voltage range is
limited from 0.6V to 3.3V.
Component Placement
Sensing the Output Voltage with a Differential
Ampli?er
The LTC3811 includes a low offset, unity gain, high band-
width differential ampli?er for applications that require true
remote sensing. Sensing both SENSE + and SENSE – greatly
bene?ts regulation in high current, low voltage applications,
where board interconnection losses can be a signi?cant
portion of the total error budget.
The LTC3811 differential ampli?er has a typical output slew
rate of 8V/μs and has rail-to-rail output drive capability.
The ampli?er is con?gured for unit gain, meaning that the
difference between SENSE + and SENSE – is translated to
DIFFOUT, relative to SGND.
Care should be taken to route the SENSE + and SENSE – PCB
traces parallel to each other all the way to the terminals
of the output capacitor or remote sensing points on the
board. In addition, avoid routing these sensitive traces near
any high speed switching nodes in the circuit. Ideally, the
SENSE + and SENSE – traces should be shielded by a low
impedance ground plane to maintain signal integrity.
Choosing the Inductor Value and Saturation Current
Rating
The operating frequency and inductor value are interrelated
in that higher operating frequencies allow the use of smaller
inductors and capacitors. Higher frequency operation also
results in higher switching and gate drive losses, so a basic
tradeoff exists between size and ef?ciency.
3811f
23
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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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