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| 型号： | LTC3809EDD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 15/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 10-DFN |
| 标准包装： | 121 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 825kHz |
| 占空比： | 100% |
| 电源电压： | 2.75 V ~ 9.8 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 ~ 85°C |
| 封装/外壳： | 10-WFDFN 裸露焊盘 |
| 包装： | 管件 |
| 产品目录页面： | 1336 (CN2011-ZH PDF) |
LTC3809
APPLICATIONS INFORMATION
size for a ?xed inductor value, but is very dependent on
the inductance selected. As inductance increases, core
sized for the maximum RMS current must be used. The
maximum RMS capacitor current is given by:
V OUT ? ( V IN – V OUT )
losses go down. Unfortunately, increased inductance
requires more turns of wire and therefore copper losses
will increase.
C IN Re quiredI RMS ≈ I MAX ?
V IN
1 / 2
Δ V OUT RIPPLE ? ? ESR +
≈ I
?
8 ? f ? C OUT ?
V OUT = 0 . 6 V ? ? 1 + B ?
Ferrite designs have very low core losses and are pre-
ferred at high switching frequencies, so design goals can
concentrate on copper loss and preventing saturation.
Ferrite core material saturates “hard”, which means that
inductance collapses abruptly when the peak design current
is exceeded. Core saturation results in an abrupt increase
in inductor ripple current and consequent output voltage
ripple. Do not allow the core to saturate!
Molypermalloy (from Magnetics, Inc.) is a very good,
low loss core material for toroids, but is more expensive
than ferrite. A reasonable compromise from the same
manufacturer is Kool Mμ. Toroids are very space ef ?cient,
especially when several layers of wire can be used, while
inductors wound on bobbins are generally easier to sur-
face mount. However, designs for surface mount that do
not increase the height signi?cantly are available from
Coiltronics, Coilcraft, Dale and Sumida.
Schottky Diode Selection (Optional)
The schottky diode D in Figure 11 conducts current dur-
ing the dead time between the conduction of the power
MOSFETs. This prevents the body diode of the bottom
N-channel MOSFET from turning on and storing charge
during the dead time, which could cost as much as 1%
in ef ?ciency. A 1A Schottky diode is generally a good
size for most LTC3809 applications, since it conducts
a relatively small average current. Larger diode results
in additional transition losses due to its larger junction
capacitance. This diode may be omitted if the ef ?ciency
loss can be tolerated.
C IN and C OUT Selection
In continuous mode, the source current of the P-channel
This formula has a maximum value at V IN = 2V OUT ,
where I RMS = I OUT /2. This simple worst-case condition
is commonly used for design because even signi?cant
deviations do not offer much relief. Note that capacitor
manufacturer’s ripple current ratings are often based on
2000 hours of life. This makes it advisable to further derate
the capacitor or to choose a capacitor rated at a higher
temperature than required. Several capacitors may be
paralleled to meet the size or height requirements in the
design. Due to the high operating frequency of the LTC3809,
ceramic capacitors can also be used for C IN . Always consult
the manufacturer if there is any question.
The selection of C OUT is driven by the effective series
resistance (ESR). Typically, once the ESR requirement
is satis?ed, the capacitance is adequate for ?ltering. The
output ripple ( Δ V OUT ) is approximated by:
? 1 ?
?
where f is the operating frequency, C OUT is the output
capacitance and I RIPPLE is the ripple current in the induc-
tor. The output ripple is highest at maximum input voltage
since I RIPPLE increase with input voltage.
Setting Output Voltage
The LTC3809 output voltage is set by an external feed-
back resistor divider carefully placed across the output,
as shown in Figure 3. The regulated output voltage is
determined by:
? R ?
? R A ?
MOSFET is a square wave of duty cycle (V OUT /V IN ). To
prevent large voltage transients, a low ESR input capacitor
3809fc
15
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| LTC3809EMSE | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP 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) |
| LTC3809EMSE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP 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) |
| LTC3809EMSE#TR | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP 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) |
| LTC3809EMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP 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) |
| LTC3809EMSE-1 | 功能描述:IC REG CTRLR BUCK PWM CM 10-MSOP 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) |
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