- 您现在的位置：买卖IC网 > PDF目录44995 > LTC3891EUDC#PBF (LINEAR TECHNOLOGY CORP) SWITCHING CONTROLLER, 900 kHz SWITCHING FREQ-MAX, PQCC20 PDF资料下载
参数资料
| 型号： | LTC3891EUDC#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 900 kHz SWITCHING FREQ-MAX, PQCC20 |
| 封装： | 3 X 4 MM, LEAD FREE, PLASTIC, QFN-20 |
| 文件页数： | 3/32页 |
| 文件大小： | 1931K |
| 代理商： | LTC3891EUDC#PBF |
第1页第2页当前第3页第4页第5页第6页第7页第8页第9页第10页第11页第12页第13页第14页第15页第16页第17页第18页第19页第20页第21页第22页第23页第24页第25页第26页第27页第28页第29页第30页第31页第32页
LTC3891
11
3891f
OPERATION
Main Control Loop
The LTC3891 uses a constant frequency, current mode
step-down architecture. During normal operation, the
external top MOSFET is turned on when the clock for
that channel sets the RS latch, and is turned off when the
main current comparator, ICMP, resets the RS latch. The
peak inductor current at which ICMP trips and resets the
latch is controlled by the voltage on the ITH pin, which is
the output of the error amplifier, EA. The error amplifier
compares the output voltage feedback signal at the VFB
pin (which is generated with an external resistor divider
connected across the output voltage, VOUT, to ground) to
the internal 0.800V reference voltage. When the load cur-
rent increases, it causes a slight decrease in VFB relative
to the reference, which causes the EA to increase the ITH
voltage until the average inductor current matches the
new load current.
After the top MOSFET is turned off each cycle, the bottom
MOSFETisturnedonuntileithertheinductorcurrentstarts
to reverse, as indicated by the current comparator IR, or
the beginning of the next clock cycle.
INTVCC/EXTVCC Power
Power for the top and bottom MOSFET drivers and most
other internal circuitry is derived from the INTVCC pin.
When the EXTVCC pin is tied to a voltage less than 4.7V,
the VIN LDO (low dropout linear regulator) supplies 5.1V
from VIN to INTVCC. If EXTVCC is taken above 4.7V, the VIN
LDO is turned off and an EXTVCC LDO is turned on. Once
enabled, the EXTVCC LDO supplies 5.1V from EXTVCC to
INTVCC. Using the EXTVCC pin allows the INTVCC power
to be derived from a high efficiency external source such
as one of the LTC3891 switching regulator outputs.
ThetopMOSFETdriverisbiasedfromthefloatingbootstrap
capacitor, CB, which normally recharges during each cycle
through an external diode when the top MOSFET turns
off. If the input voltage, VIN, decreases to a voltage close
to VOUT, the loop may enter dropout and attempt to turn
on the top MOSFET continuously. The dropout detector
detects this and forces the top MOSFET off for about one
twelfth of the clock period every tenth cycle to allow CB
to recharge.
Shutdown and Start-Up (RUN, TRACK/SS Pins)
The LTC3891 can be shut down using the RUN pin. Pulling
this pin below 1.16V shuts down the main control loop.
Pulling the RUN pin below 0.7V disables the controller
and most internal circuits, including the INTVCC LDOs.
In this state, the LTC3891 draws only 14μA of quiescent
current.
Releasing the RUN pin allows a small internal current to
pull up the pin to enable the controller. The RUN pin has
a 7μA pull-up which is designed to be large enough so
that the RUN pin can be safely floated (to always enable
the controller) without worry of condensation or other
small board leakage pulling the pin down. This is ideal
for always-on applications where the controller is enabled
continuously and never shut down.
The RUN pin may be externally pulled up or driven directly
by logic. When driving the RUN pin with a low impedance
source, do not exceed the absolute maximum rating of
8V. The RUN pin has an internal 11V voltage clamp that
allows the RUN pin to be connected through a resistor to a
higher voltage (for example, VIN),solongasthemaximum
current into the RUN pin does not exceed 100μA.
The RUN pin can also be implemented as a UVLO by
connecting it to the output of an external resistor divider
network off VIN (see Applications Information section).
The start-up of the controller’s output voltage VOUT is
controlled by the voltage on the TRACK/SS pin. When the
voltage on the TRACK/SS pin is less than the 0.8V internal
reference, the LTC3891 regulates the VFB voltage to the
TRACK/SS pin voltage instead of the 0.8V reference. This
allowstheTRACK/SSpintobeusedtoprogramasoft-start
by connecting an external capacitor from the TRACK/SS
pin to SGND. An internal 10μA pull-up current charges
this capacitor creating a voltage ramp on the TRACK/SS
pin. As the TRACK/SS voltage rises linearly from 0V to
0.8V (and beyond up to 5V), the output voltage VOUT rises
smoothly from zero to its final value. Alternatively the
TRACK/SS pin can be used to cause the start-up of VOUT
to track that of another supply. Typically, this requires
connecting to the TRACK/SS pin an external resistor
divider from the other supply to ground (see Applications
Information section).
相关PDF资料 |
PDF描述 |
|---|---|
| LTC3900MPS8#TR | SWITCHING REGULATOR, PDSO8 |
| LTC3900MPS8#PBF | SWITCHING REGULATOR, PDSO8 |
| LTC3900HS8 | SWITCHING REGULATOR, PDSO8 |
| LTC3900HS8#TRPBF | SWITCHING REGULATOR, PDSO8 |
| LTC3900HS8#TR | SWITCHING REGULATOR, PDSO8 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3891HFE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 20TSSOP 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: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 |
| LTC3891HFE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 20TSSOP 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: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 |
| LTC3891HUDC#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 20-QFN 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: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 |
| LTC3891HUDC#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 20-QFN 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: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 |
| LTC3891IFE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 20TSSOP 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: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 |
发布紧急采购，3分钟左右您将得到回复。