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参数资料
| 型号： | LTC3805EDD-5#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST FLYBK PWM 10DFN |
| 标准包装： | 2,500 |
| 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-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 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 |
LTC3805-5
APPLICATIONS INFORMATION
N BIAS = N SEC
ManyLTC3805-5applicationcircuitscanbederivedfrom
the topologies shown on the first page or in the Typical
Applications section of this data sheet.
The LTC3805-5 itself imposes no limits on allowed input
voltage V IN or output voltage V OUT . These are all determined
by the ratings of the external power components. In Figure 8,
the factors are: Q1 maximum drain-source voltage (B VDSS ),
on-resistance (R DS(ON) ) and maximum drain current, T1
saturation flux level and winding insulation breakdown
voltages, C IN and C OUT maximum working voltage, equiva-
lent series resistance (ESR), and maximum ripple current
ratings, and D1 and R SENSE power ratings.
V CC Bias Power
The V CC pin must be bypassed to the GND pin with a
minimum 1μF ceramic or tantalum capacitor located im-
mediately adjacent to the two pins. Proper supply bypassing
is necessary to supply the high transient currents required
by the MOSFET gate driver.
For maximum flexibility, the LTC3805-5 is designed so
that it can be operated from voltages well beyond the
LTC3805-5’s absolute maximum ratings. Figure 2 shows
the simplest case, in which the LTC3805-5 is powered
with a resistor R VCC connected between the input voltage
and V CC . The built-in shunt regulator limits the voltage on
the V CC pin to around 9.5V as long as the internal shunt
regulator is not forced to sink more than 25mA. This pow-
ering scheme has the drawback that the power loss in the
resistor reduces converter efficiency and the 25mA shunt
regulator maximum may limit the maximum-to-minimum
range of input voltage.
V IN
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 providing
bias power to the LTC3805-5. A small NPN preregulator
transistor and a Zener diode are used to accelerate the
rise of V CC and reduce the value of the V CC 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 V CC bias power for
the LTC3805-5. The number of turns in the bias winding
is chosen according to
V CC + V D2
V OUT + V D1
where N BIAS is the number of turns in the bias winding,
N SEC is the number of turns in the secondary winding,
V CC is the desired voltage to power the LTC3805-5, V OUT
is the converter output voltage, V D1 is the forward voltage
drop of D1 and V D2 is the forward voltage drop of D2.
Note that since V OUT is regulated by the converter control
loop, V CC is also regulated although not as precisely. If an
“off-the-shelf” transformer with excessive bias windings
is used, the resistor, R BIAS in Figure 9, can be added to
limit the current.
Transformer Design Considerations
Transformer specification 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.
R VCC
LTC3805-5
Turns Ratios
C VCC
V CC
GND
38055 F02
Figure 2. Powering the LTC3805-5 via the
Internal Shunt Regulator
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
38055fe
11
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3805EMSE | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Sync Flyback 8.8V to 75V Input 10-Pin MSOP EP |
| LTC3805EMSE#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) |
| LTC3805EMSE#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) |
| LTC3805EMSE-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:- 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) |
| LTC3805EMSE-5#PBF | 制造商:Linear Technology 功能描述:IC, FLYBACK/ BOOST/SEPIC CTRL, MSOP-10 |
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