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参数资料
| 型号： | LTC3805MPMSE#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, 700 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | PLASTIC, MSOP-10 |
| 文件页数： | 4/20页 |
| 文件大小： | 248K |
| 代理商： | LTC3805MPMSE#TR |
LTC3805
12
3805ff
APPLICATIONS INFORMATION
CVCC is charged to VTURNON. At this point, assuming VRUN
> VRUNON, the converter begins switching the external
MOSFET and ramps up the converter output voltage at
a rate set by the capacitor CSS on the SSFLT pin. Since
RSTART cannot supply enough current to operate the ex-
ternal MOSFET, CVCC begins discharging and VCC drops.
The soft-start must be fast enough and the discharge of
CVCC slow enough so that the output voltage reaches its
target value of 5V before VCC drops to VTURNOFF or the
converter would fail to start.
The typical application circuit in Figure 9 shows a different
flyback converter bias power strategy for a case in which
neither the input or output voltage is suitable for provid-
ing bias power to the LTC3805. A small NPN preregulator
transistor and a Zener diode are used to accelerate the
rise of VCC and reduce the value of the VCC bias capacitor.
The flyback transformer has an additional bias winding to
provide bias power. Note that this topology is very power-
ful because, by appropriate choice of transformer turns
ratio, the output voltage can be chosen without regard to
the value of the input voltage or the VCC bias power for
the LTC3805. The number of turns in the bias winding is
chosen according to
NBIAS = NSEC
VCC + VD4
VOUT VD1
where NBIAS is the number of turns in the bias winding,
NSEC is the number of turns in the secondary winding,
VCC is the desired voltage to power the LTC3805, VOUT is
the converter output voltage, VD1 is the forward voltage
drop of D1 and VD4 is the forward voltage drop of D4.
Note that since VOUT is regulated by the converter control
loop, VCC is also regulated although not as precisely. The
value of VCC is often constrained since NBIAS and NSEC are
often a limited range of small integer numbers. For proper
operation, the value of VCC must be between VTURNON and
VTURNOFF. Since the ratio of VTURNON to VTURNOFF is over
two to one, this requirement is relatively easy to satisfy.
Figure 9 shows a similar low power nonisolated telecom
converter using a trickle charger.
Transformer Design Considerations
Transformer specification and design is perhaps the
most critical part of applying the LTC3805 successfully.
In addition to the usual list of caveats dealing with high
frequencypowertransformerdesign,thefollowingshould
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”
configurable 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 flyback pulse (including leakage
spike) must not exceed the allowed external MOSFET
breakdown rating.
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相关代理商/技术参数 |
参数描述 |
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| LTC3806EDE | 功能描述:IC REG CTRLR FLYBACK PWM 12-DFN RoHS:否 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) |
| LTC3806EDE#PBF | 功能描述:IC REG CTRLR FLYBACK PWM 12-DFN 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) |
| LTC3806EDE#TR | 功能描述:IC REG CTRLR FLYBACK PWM 12-DFN RoHS:否 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) |
| LTC3806EDE#TRPBF | 功能描述:IC REG CTRLR FLYBACK PWM 12-DFN 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) |
| LTC3808EDE | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Sync Step Down 2.75V to 9.8V Input 14-Pin DFN EP |
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