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| 型号： | LTC3853EUJ#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/36页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 40-QFN |
| 产品培训模块： | LTC3853 Multiphase Switching Controller |
| 标准包装： | 61 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 3 |
| 频率 - 最大： | 830kHz |
| 占空比： | 98% |
| 电源电压： | 4.5 V ~ 24 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 ~ 125°C |
| 封装/外壳： | 40-WFQFN 裸露焊盘 |
| 包装： | 管件 |
| 产品目录页面： | 1336 (CN2011-ZH PDF) |
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LTC3853
OPERATION
Main Control Loop
The LTC3853 is a constant-frequency, current mode
step-down controller with three channels operating 120
degrees out-of-phase. During normal operation, each
top MOSFET is turned on when the clock for that channel
sets the RS latch, and 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 I TH pin, which is the output of each 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 I TH voltage to increase until the average
inductor current matches the new load current. After the
top MOSFET has turned off, the bottom MOSFET is turned
on until either the inductor current starts to reverse, as
indicated by the reverse current comparator I REV , or the
beginning of the next cycle.
INTV CC /EXTV CC /DRV CC12 Power
Power for the top and bottom MOSFET drivers of phase 3
and most other internal circuitry is derived from the
INTV CC pin. DRV CC12 provides driver power for phase 1
and phase 2. This pin must be externally tied to INTV CC .
If EXTV CC is taken above 4.7V, the 5V regulator is turned
off and an internal switch is turned on connecting EXTV CC .
Using the EXTV CC pin allows the INTV CC power to be derived
from a high efficiency external source such as one of the
LTC3853 switching regulator outputs.
Each top MOSFET driver is biased from the floating boot-
strap capacitor, C B , which normally recharges during each
off cycle through an external 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 detec-
tor detects this and forces the top MOSFET off for about
one-twelfth of the clock period every fifth cycle to allow
C B to recharge. However, it is recommended that there is
always a load be present during the drop-out transition
to ensure C B is recharged.
Shutdown and Start-Up (RUN1, RUN2, RUN3 and
TK/SS1, TK/SS2, TK/SS3 Pins)
The three channels of the LTC3853 can be independently
shut down using the RUN1, RUN2 and RUN3 pins. Pulling
any of these pins below 1.2V shuts down the main control
loop for that controller. Pulling all pins low disables all
three controllers and most internal circuits, including the
INTV CC regulator. Releasing any RUN pin allows an internal
0.5μA current to pull up the pin and enable that control-
ler. Alternatively, the RUN 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 each controller’s output voltage V OUT is
controlled by the voltage on the TK/SS1, TK/SS2 and
TK/SS3 pins. When the voltage on the TK/SS pin is less
than the 0.8V internal reference, the LTC3853 regulates
the V FB voltage to the TK/SS pin voltage instead of the
0.8V reference. This allows the TK/SS pin to be used to
program a soft-start by connecting an external capacitor
from the TK/SS pin to SGND. An internal 1.3μA pull-up
current charges this capacitor, creating a voltage ramp
on the TK/SS pin. As the TK/SS voltage rises linearly
from 0V to 0.8V (and beyond), the output voltage V OUT
rises smoothly from zero to its final value. Alternatively
the TK/SS pin can be used to cause the start-up of V OUT
to “track” that of another supply. Typically, this requires
connecting to the TK/SS pin an external resistor divider
from the other supply to ground (see the Applications
Information section). When the corresponding RUN pin
is pulled low to disable a controller, or when INTV CC drops
below its undervoltage lockout threshold of 3.35V, the
TK/SS pin is pulled low by an internal MOSFET. When in
undervoltage lockout, all controllers are disabled and the
external MOSFETs are held off.
Light Load Current Operation (Burst Mode Operation,
Pulse Skipping or Continuous Conduction)
The LTC3853 can be enabled to enter high efficiency Burst
Mode operation, constant-frequency pulse skipping mode,
or forced continuous conduction mode. To select forced
continuous operation, tie the MODE/PLLIN pin to a DC
3853fa
11
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相关代理商/技术参数 |
参数描述 |
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| LTC3853IUJ#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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 ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC3853IUJ#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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 ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC3854EDDB#PBF | 制造商:Linear Technology 功能描述:DP-SWREG/Controller, Cut Tape Small Footprint, Low Pin Count Synchronous Step-Do |
| LTC3854EDDB#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) |
| LTC3854EDDB#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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