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参数资料
| 型号： | LTC3854EDDB#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 12-DFN |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 440kHz |
| 占空比： | 98% |
| 电源电压： | 4.5 V ~ 38 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： | 12-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
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LTC3854
OPERATION
Main Control Loop
The LTC3854 is a constant-frequency, peak current mode
step-down controller. During normal operation, the top
MOSFET is turned on when the clock sets the RS latch,
and is turned off when the main current comparator, I CMP ,
resets the RS latch. The peak inductor current at which
I CMP resets the RS latch is controlled by the voltage on
the ITH pin, which is the output of the error amplifier EA.
The V FB pin receives the voltage feedback signal, which is
compared to the internal reference voltage by the EA. When
the load current increases, it causes a slight decrease in
V FB relative to the 0.8V reference, which in turn causes
the ITH voltage to increase until the average inductor cur-
rent matches the new load current. After the top MOSFET
has turned off, the bottom MOSFET is turned on until the
beginning of the next cycle.
INTV CC Power
Power for the top and bottom MOSFET drivers and most
other internal circuitry is derived from the INTV CC pin. An
internal 5V low dropout linear regulator supplies INTV CC
power from V IN .
The top MOSFET driver is biased from a floating bootstrap
capacitor C B , which recharges during each off cycle through
an external Schottky diode when the top MOSFET turns
off. If the input voltage V IN decreases to a voltage close to
V OUT , the loop may enter dropout and attempt to turn on
the top MOSFET continuously. The dropout detector then
forces the top MOSFET off for 1/10 of the clock period
every fourth cycle to allow C B to recharge.
Shutdown and Start-Up (RUN/SS)
The LTC3854 is shut down using the RUN/SS pin. Pulling
this pin below 1.2V disables the controller and most of the
internal circuitry, including the INTV CC regulator.
However, for RUN/SS>0.8V the internal bandgap is
functional and the input current will be greater than the
minimum shutdown current. To keep the part in a true
shutdown mode the RUN/SS pin should be held below 0.4V.
Releasing RUN/SS pin allows an internal 1.25μA current to
pull up the pin and enable the controller. Alternatively, the
RUN/SS pin may be externally pulled up or driven directly
by logic. Be careful not to exceed the Absolute Maximum
Rating of 6V on this pin.
The start-up of the controller’s output voltage V OUT
is governed by the voltage on the RUN/SS pin until
RUN/SS > 2V.
When the voltage on the RUN/SS pin is greater than 1.2V
and less than 2V the LTC3854 regulates the V FB voltage to
1.2V below the RUN/SS pin voltage. The RUN/SS pin pro-
grams the soft-start period through an external capacitor
from the RUN/SS pin to GND. An internal 1.25μA pull-up
current charges this capacitor creating a voltage ramp on
the RUN/SS pin. As the RUN/SS voltage rises linearly from
1.2V to 2V, V OUT rises smoothly from zero to the target
output voltage. When the LTC3854 is in undervoltage
lockout the external MOSFETs are held off.
Frequency of Operation
The LTC3854 operates at a fixed frequency of 400kHz.
Output Overvoltage Protection
An overvoltage comparator, OV, guards against transient
overshoots (>10%) as well as other more serious condi-
tions that may overvoltage the output. In such cases, the
top MOSFET is turned off and the bottom MOSFET is turned
on until the overvoltage condition is cleared.
3854fb
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相关代理商/技术参数 |
参数描述 |
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| LTC3854EMSE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 12-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 |
| LTC3854EMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 12-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) |
| LTC3854IDDB#PBF | 制造商:Linear Technology 功能描述:DP-SWREG/Controller, Cut Tape Small Footprint, Low Pin Count Synchronous Step-Do |
| LTC3854IDDB#TRMPBF | 功能描述:IC REG CTRLR BUCK PWM CM 12-DFN 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) |
| LTC3854IDDB#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 12-DFN 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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