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| 型号： | LTC1771ES8#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 8-SOIC |
| 标准包装： | 100 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 占空比： | 100% |
| 电源电压： | 2.8 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： | -40°C ~ 85°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1333 (CN2011-ZH PDF) |
LTC1771
APPLICATIO S I FOR ATIO
continuous mode, I GATECHG = fQ P where Q P is the gate
charge of the internal switch. Both the DC bias and gate
charge losses are proportional to V IN and thus their
effects will be more pronounced at higher supply
To minimize no-load supply current, resistor values in the
megohm range should be used. The increase in supply
current due to the feedback resistors can be calculated
from:
R 1 + R 2 ? V IN ?
voltages.
3. I 2 R losses are predicted from the internal switch, induc-
tor and current sense resistor. In continuous mode the
? I VIN =
V OUT ? V OUT ?
? ?
average output current flows through L but is “chopped”
between the P-channel MOSFET in series with R SENSE
and the output diode. The MOSFET R DS(ON) plus R SENSE
multiplied by the duty cycle can be summed with the
resistance of L to obtain I 2 R losses.
4. The catch diode loss is proportional to the forward drop
as the diode conducts current during the off-time and is
more pronounced at high supply voltages where the
off-time is long. However, as discussed in the Catch
Diode section, diodes with lower forward drops often
have higher leakage currents, so although efficiency is
improved, the no-load supply current will increase. The
diode loss is calculated by multiplying the forward
voltage drop times the diode duty cycle multiplied by
the load current.
Other losses including C IN and C OUT ESR dissipative
losses, and inductor core losses, generally account for
less than 2% total additional loss.
Output Voltage Programming
The output voltage is programmed with an external divider
from V OUT to V FB (Pin 1) as shown in Figure 2. The
regulated voltage is determined by:
A 5pF feedforward capacitor across R2 is recommended
to minimize output voltage ripple in Burst Mode operation.
Run/Soft-Start Function
The RUN/SS pin is a dual purpose pin that provides the
soft- start function and a means to shut down the LTC1771.
Soft-start reduces the input surge current from V IN by
gradually increasing the internal current limit. Power
supply sequencing can also be accomplished using
this pin.
An internal 1 μ A current source charges up an external
capacitor C SS . When the voltage on the RUN/SS reaches
1V, the LTC1771 begins operating. As the voltage on the
RUN/SS continues to ramp from 1V to 2.2V, the internal
current limit is also ramped at a proportional linear rate.
The current limits begins near 40% maximum load at
V RUN/SS = 1V and ends at maximum load at V RUN/SS =
2.2V. The output current thus ramps up slowly, reducing
the starting surge current required from the input power
supply. If the RUN/SS has been pulled all the way to
ground, there will be a delay before the current limit starts
increasing and is given by:
t DELAY ≈ C SS /I CHG
V OUT = 1 . 23 ? 1 +
?
?
?
R 2 ?
R 1 ?
V OUT
where I CHG ? 1 μ A. Pulling the RUN/SS pin below 0.5V
puts the LTC1771 into a low quiescent current shutdown
(I Q < 2 μ A).
Foldback Current Limiting
V FB
R2
C FF
5pF
As described in the Catch Diode Selection, the worst-case
dissipation for diode occurs with a short-circuit output,
when the diode conducts the current limit value almost
LTC1771
GND
R1
1771 F02
continuously. In most applications this will not cause
excessive heating, even for extended fault intervals. How-
ever, when heat sinking is at a premium or higher forward
voltage drop diodes are being used, foldback current
Figure 2. LTC1771 Adjustable Configuaration
10
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC1771IS8 | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC RoHS:否 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) |
| LTC1771IS8#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC 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:2,000 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:1MHz 占空比:50% 电源电压:9 V ~ 10 V 降压:无 升压:是 回扫:是 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:8-TSSOP（0.173"，4.40mm 宽） 包装:带卷 (TR) |
| LTC1771IS8#TR | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC RoHS:否 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) |
| LTC1771IS8#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC 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) |
| LTC1772BES6 | 制造商:Linear Technology 功能描述:IC CTRLR DC/DC S-DWN SOT23-6 |
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