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参数资料
| 型号： | LTC3805HMSE-5#TRMPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 700 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | LEAD FREE, PLASTIC, MSOP-10 |
| 文件页数： | 4/20页 |
| 文件大小： | 203K |
| 代理商： | LTC3805HMSE-5#TRMPBF |
LTC3805-5
12
38055fb
APPLICATIONS INFORMATION
Transformer Design Considerations
Transformer specication and design is perhaps the most
critical part of applying the LTC3805-5 successfully. In
addition to the usual list of caveats dealing with high fre-
quency power transformer design, the following should
prove useful.
Turns Ratios
Due to the use of the external feedback resistor divider
ratio to set output voltage, the user has relative freedom
in selecting transformer turns ratio to suit a given ap-
plication. Simple ratios of small integers, e.g., 1:1, 2:1,
3:2, etc. can be employed which yield more freedom in
setting total turns and transformer inductance. Simple
integer turns ratios also facilitate the use of “off-the-shelf”
congurable transformers. Turns ratio can be chosen on
the basis of desired duty cycle. However, remember that
the input supply voltage plus the secondary-to-primary
referred version of the yback 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
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 bilar 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 bilar
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
LTC3805-5 sources 5μA out of the RUN pin when operation
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
VV
RR
R
RA
IN RUN FALLING
RUNOFF
(,
)
=
+
12
2
15
μ
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 VIN is simply
VV
RR
R
IN RUN RISING
RUNON
(,
)
=
+
12
2
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.
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| 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) |
| LTC3805IDD#TRPBF | 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) |
| LTC3805IDD-5#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) |
| LTC3805IDD-5#TRPBF | 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) |
| LTC3805IMSE#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: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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