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| 型号： | LTC1771EMS8 |
| 厂商： | Linear Technology |
| 文件页数： | 8/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 8-MSOP |
| 标准包装： | 50 |
| 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-TSSOP，8-MSOP（0.118"，3.00mm 宽） |
| 包装： | 管件 |
| 其它名称： | Q1164777 |
LTC1771
APPLICATIO S I FOR ATIO
R DS ( ON ) =
( ) ( 1 + δ P )
Power MOSFET Selection
An external P-channel power MOSFET must be selected
for use with the LTC1771. The main selection criteria for
the power MOSFET are the threshold voltage V GS(TH) and
the “on” resistance R DS(ON) , reverse transfer capacitance
and total gate charge.
Since the LTC1771 can operate down to input voltages as
low as 2.8V, a sublogic level threshold MOSFET (R DS(ON)
guaranteed at V GS = 2.5V) is required for applications that
work close to this voltage. When these MOSFETs are used,
make sure that the input supply to the LTC1771 is less than
the absolute maximum V GS rating (typically 12V), as the
MOSFET gate will see the full supply voltage.
The required R DS(ON) of the MOSFET is governed by its
allowable power dissipation. For applications that may
operate the LTC1771 in dropout, i.e. 100% duty cycle, at
its worst case the required R DS(ON) is given by:
P P
2
I OUT ( MAX )
where P P is the allowable power dissipation and δ P is the
temperature dependency of R DS(ON) . (1 + δ P ) is generally
diode conducts most of the time. As V IN approaches V OUT
the diode conducts only a small fraction of the time. The
most stressful condition for the diode is when the output
is short-circuited. Under this condition, the diode must
safely handle I PEAK at close to 100% duty cycle.
To maximize both low and high current efficiencies, a fast
switching diode with low forward drop and low reverse
leakage should be used. Low reverse leakage current is
critical to maximize low current efficiency since the leak-
age can potentially exceed the magnitude of the LTC1771
supply current. Low forward drop is critical for high
current efficiency since loss is proportional to forward
drop. The effect of reverse leakage and forward drop on
no- load supply current and efficiency for various Schottky
diodes is shown in Table 1. As can be seen, these are
conflicting parameters and the user must weigh the
importance of each spec in choosing the best diode for the
application.
Table 1. Effect of Catch Diode on Performance
LEAKAGE NO-LOAD EFFICIENCY
DIODE (V R = 3.3V) V F @ 1A SUPPLY CURRENT AT 10V/1A
MBR0540 0.25 μ A 0.50V 10.4 μ A 86.3%
UPS5817 2.8 μ A 0.41V 11.8 μ A 88.2%
MBR0520 3.7 μ A 0.36V 12.2 μ A 88.4%
given for a MOSFET in the form of a normalized R DS(ON) vs
temperature curve, but = 0.005/ ° C can be used as an
approximation for low voltage MOSFETs.
MBRS120T3
MBRM120LT3
MBRS320
4.4 μ A
8.3 μ A
19.7 μ A
0.43V
0.32V
0.29V
12.2 μ A
14.0 μ A
20.0 μ A
87.9%
89.4%
89.8%
In applications where the maximum duty cycle is less than
100% and the LTC1771 is in continuous mode, the R DS(ON)
is governed by:
C IN and C OUT Selection
At higher load currents, when the inductor current is
R DS ( ON ) =
DC =
P P
( DC ) I OUT 2 ( 1 + δ P )
V OUT + V D
V IN + V D
continuous, the source current of the P-channel MOSFET
is a square wave of duty cycle V OUT /V IN . To prevent large
voltage transients, a low ESR input capacitor sized for the
maximum RMS current must be used. The maximum
capacitor current is given by:
I MAX [ OUT ( V IN ? V OUT ) ] 1 / 2
where DC is the maximum operating duty cycle of the
LTC1771.
C IN required I RMS =
V
V IN
Catch Diode Selection
The catch diode carries load current during the off-time.
The average diode current is therefore dependent on the
P-channel switch duty cycle. At high input voltages the
8
This formula has a maximum at V IN = 2V OUT , where
I RMS = I OUT /2. This simple worst-case condition is com-
monly used for design because even significant deviations
do not offer much relief. Note that capacitor manufacturer’s
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC1771EMS8#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 8-MSOP 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 |
| LTC1771EMS8#PBF | 制造商:Linear Technology 功能描述:IC STEP-DOWN DC/DC CONTROLLER MSOP-8 制造商:Linear Technology 功能描述:IC, STEP-DOWN DC/DC CONTROLLER, MSOP-8 |
| LTC1771EMS8#TR | 功能描述:IC REG CTRLR BUCK PWM CM 8-MSOP 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) |
| LTC1771EMS8#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 8-MSOP 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) |
| LTC1771EMS8PBF | 制造商:Linear Technology 功能描述:PWM Controller Current 1.23-18V 5A MSOP8 |
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