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| 型号： | LTC3805IMSE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/20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 ~ 125°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
OPERATION
f OSC =
Start-Up/Shutdown
The LTC3805 has two shutdown mechanisms to disable
and enable operation: an undervoltage lockout on the V CC
supply pin voltage, and a precision-threshold RUN pin. The
voltage on both pins must exceed the appropriate thresh-
old before operation is enabled. The LTC3805 transitions
into and out of shutdown according to the state diagram
shown in Figure 1. Operation in fault timeout is discussed
in a subsequent section. During shutdown the LTC3805
draws only a small 40μA current.
The undervoltage lockout (UVLO) mechanism prevents
the LTC3805 from trying to drive the external MOSFET
gate with insufficient voltage on the V CC pin. The voltage
at the V CC pin must initially exceed V TURNON = 8.4V to
enable LTC3805 operation. After operation is enabled, the
voltage on the V CC pin may fall as low as V TURNOFF = 4V
before undervoltage lockout disables the LTC3805. This
wide UVLO hysteresis range supports the use of trickle
charger powering schemes. See the Applications Informa-
tion section for more detail.
The RUN pin is connected to the input voltage using a
voltage divider. Converter operation is enabled when the
voltage on the RUN pin exceeds V RUNON = 1.207V and
disabled when the voltage falls below V RUNOFF = 1.170V.
Additional hysteresis is added by a 5μA current source
acting on the voltage divider’s Thevenin resistance. Setting
the input voltage range and hysteresis is further discussed
in the Applications Information section.
Setting the Oscillator Frequency
Connect a frequency set resistor R FS from the FS pin to
ground to set the oscillator frequency over a range from
70kHz to 700kHz. The oscillator frequency is calculated
from:
24 ? 10 9
R FS ? 1500
The oscillator may be synchronized to an external clock
using the SYNC input. The rising edge of the external clock
on the SYNC pin triggers the beginning of a switching
period, i.e., the GATE pin going high. The pulse width of
the external clock is quite flexible.
Overcurrent Protection
With the OC pin connected to the external MOSFET’s current
sense resistor, the converter is protected in the event of
an overload or short-circuit on the output. During normal
operation the peak value of current in the external MOS-
FET, as measured by the current sense resistor (plus any
adjustment for slope compensation), is set by the voltage
on the I TH pin operating through the current comparator.
As the output current increases, so does the voltage on
the I TH pin and so does the peak MOSFET current.
V RUN > V RUNON
AND V CC > V TURNON
LTC3805
SHUTDOWN
V SSFLT < 0.7V
V RUN < V RUNOFF
V CC < V TURNOFF
LTC3805
FAULT
TIMEOUT
LTC3805
ENABLED
V OC > 100mV
3805 F01
Figure 1. Start-Up/Shutdown State Diagram
3805fg
9
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| LTC3805MPMSE#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:- 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 |
| LTC3805MPMSE#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: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 |
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