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| 型号： | LTC3805EMSE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 13/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST FLYBK CM 10MSOP |
| 标准包装： | 50 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 700kHz |
| 占空比： | 95% |
| 电源电压： | 3.95 V ~ 75 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： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 相关产品： | 732-2264-6-ND - TRANS FLYBACK LTC3805 36.3UH 732-2264-1-ND - TRANS FLYBACK LTC3805 36.3UH 732-2264-2-ND - TRANS FLYBACK LTC3805 36.3UH |
LTC3805
APPLICATIONS INFORMATION
V IN(RUN,RISING) = V RUNON ?
V IN(RUN,FALLING) = V RUNOFF ?
? R1 ? 5μA
V OUT ? 0.8V
R3 = R4
LeakageInductance
Transformer leakage inductance (on either the primary
or secondary) causes a voltage spike to occur after the
MOSFET (Q1) turn-off. This is increasingly prominent at
higher load currents, where more stored energy must be
dissipated. In some cases an RC “snubber” circuit will be
required to avoid overvoltage breakdown at the MOSFET’s
drain node. Application Note 19 is a good reference on
snubber design. A bifilar or similar winding technique is a
good way to minimize troublesome leakage inductances.
However, remember that this will limit the primary-to-
secondary breakdown voltage, so bifilar winding is not
always practical.
Setting Undervoltage and Hysteresis on V IN
The RUN pin is connected to a resistive voltage divider
connected to V IN as shown in Figure 4. The voltage thresh-
old for the RUN pin is V RUNON rising and V RUNOFF falling.
Note that V RUNON – V RUNOFF = 35mV of built-in voltage
hysteresis that helps eliminate false trips.
To introduce further user-programmable hysteresis, the
LTC3805 sources 5μA out of the RUN pin when operation
of LTC3805 is enabled. As a result, the falling threshold
for the RUN pin also depends on the value of R1 and can
be programmed by the user. The falling threshold for V IN
is therefore
R1 + R2
R2
V IN
RUN
R1
where R1(5μA) is the additional hysteresis introduced
by the 5μA current sourced by the RUN pin. When in
shutdown, the RUN pin does not source the 5μA current
and the rising threshold for V IN is simply
R1 + R2
R2
External Run/Stop Control
To implement external run control, place a small N-channel
MOSFET from the RUN pin to GND as shown in Figure 4.
Drive the gate of this MOSFET high to pull the RUN pin
to ground and prevent converter operation.
Selecting Feedback Resistor Divider Values
The regulated output voltage is determined by the resistor
divider across V OUT (R3 and R4 in Figure 2). The ratio of R4
to R3 needed to produce a desired V OUT can be calculated:
0.8V
Choose resistance values for R3 and R4 to be as large as
possible in order to minimize any efficiency loss due to
the static current drawn from V OUT , but just small enough
so that when V OUT is in regulation the input current to the
V FB pin is less than 1% of the current through R3 and R4.
A good rule of thumb is to choose R4 to be less than 80k.
LTC3805
GND
R2
3805 F04
RUN/STOP
CONTROL
(OPTIONAL)
Figure 4. Setting RUN Pin Voltage and Run/Stop Control
3805fg
13
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| LTC3805HMSE#PBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP 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 |
| LTC3805HMSE#TRPBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP 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) |
| LTC3805HMSE-5#PBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP 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 |
| LTC3805HMSE-5#TRPBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP 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) |
| LTC3805IDD#PBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN 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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