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參數(shù)資料
| 型號： | LTC3805HMSE-5#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 700 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封裝： | LEAD FREE, PLASTIC, MSOP-10 |
| 文件頁數(shù)： | 4/20頁 |
| 文件大小： | 265K |
| 代理商： | LTC3805HMSE-5#TRPBF |
LTC3805-5
38055fd
applications inForMation
the basis of desired duty cycle. However, remember that
the input supply voltage plus the secondary-to-primary
referred version of the flyback pulse (including leakage
spike) must not exceed the allowed external MOSFET
breakdown rating.
Leakage Inductance
Transformer leakage inductance (on either the primary
or secondary) causes a voltage spike to occur after the
turn off of MOSFET (Q1) in Figure 8. This is increasingly
prominent at higher load currents, where more stored
energymustbedissipated.InsomecasesanRC“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 leak-
age 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 VIN
The RUN pin is connected to a resistive voltage divider
connected to VIN as shown in Figure 3. The voltage thresh-
old for the RUN pin is VRUNON rising and VRUNOFF falling.
Note that VRUNON – VRUNOFF = 35mV of built-in voltage
hysteresis that helps eliminate false trips.
To introduce further user-programmable hysteresis, the
LTC3805-5sources5AoutoftheRUNpinwhenoperation
of LTC3805-5 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 VIN
is therefore
VIN(RUN,FALLING) = VRUNOFF
R1
+R2
R2
R1 5A
where R1(5A) is the additional hysteresis introduced
by the 5A current sourced by the RUN pin. When in
shutdown, the RUN pin does not source the 5A current
and the rising threshold for VIN is simply
VIN(RUN,RISING) = VRUNON
R1
+R2
R2
Note that for some applications the RUN pin can be con-
nected to VCC in which case the VCC thresholds, VTURNON
and VTURNOFF, control operation.
External Run/Stop Control
Toimplementexternalruncontrol,placeasmallN-channel
MOSFET from the RUN pin to GND as shown in Figure 3.
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 VOUT (R3 and R4 in Figure 8). The ratio
of R4 to R3 needed to produce a desired VOUT can be
calculated:
R3
=
VOUT 0.8V
0.8V
R4
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 VOUT, but just small enough so
that when VOUT is in regulation the input current to the VFB
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.
Figure 3. Setting RUN Pin Voltage and Run/Stop Control
LTC3805-5
RUN
RUN/STOP
CONTROL
(OPTIONAL)
R1
R2
GND
38055 F03
VIN
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| LTC3805IDD#PBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3805IDD#TRPBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3805IDD-5#PBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3805IDD-5#TRPBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3805IMSE#PBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
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