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| 型号： | LTC3879EUD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 14/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-QFN |
| 标准包装： | 121 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 2MHz |
| 占空比： | 90% |
| 电源电压： | 4 V ~ 38 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： | 16-WFQFN 裸露焊盘 |
| 包装： | 管件 |
| 产品目录页面： | 1336 (CN2011-ZH PDF) |
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LTC3879
APPLICATIONS INFORMATION
A reasonable starting point is to choose a ripple current
that is about 40% of I OUT(MAX) . The largest ripple current
occurs at the highest V IN . To guarantee that ripple current
does not exceed a speci?ed maximum, the inductance
should be chosen according to:
This formula has a maximum at V IN = 2V OUT , where I RMS
= I OUT(MAX) /2. This simple worst-case condition is com-
monly used for design because even signi?cant deviations
do not offer much relief. Note that ripple current ratings
from capacitor manufacturers are often based on only
? ? ?
L = ?
? ? 1 –
V OUT ?
V OUT
? f OP ? Δ I IL ( MAX ) ? ?
?
V IN ( MAX ) ?
2000 hours of life, which makes it advisable to de-rate
the capacitor.
The selection of C OUT is primarily determined by the ESR
Δ V OUT L ? ESR +
≤ Δ I
Once the value for L is known, the type of inductor must
be selected. High ef?ciency converters generally cannot
tolerate the core loss of low cost powdered iron cores,
forcing the use of more expensive ferrite materials such as
molypermalloy or Kool Mμ ? cores. A variety of inductors
designed for high current, low voltage applications are
available from manufacturers such as Sumida, Panasonic,
Coiltronics, Coilcraft, Toko, Vishay, Pulse and Wurth.
Inductor Core Selection
Once the inductance value is determined, the type of in-
ductor must be selected. Core loss is independent of core
size for a ?xed inductor value, but it is very dependent
on inductance selected. As inductance increases, core
losses go down. Unfortunately, increased inductance
requires more turns of wire and therefore copper losses
will increase.
Ferrite designs have very low core loss and are preferred
at high switching frequencies, so design goals can con-
centrate on copper loss and preventing saturation. Ferrite
core material saturates “hard,” which means that induc-
tance collapses abruptly when the peak design current is
exceeded. This results in an abrupt increase in inductor
ripple current and consequent output voltage ripple. Do
not allow the core to saturate!
C IN and C OUT Selection
The input capacitance C IN is required to ?lter the square
wave current at the drain of the top MOSFET. Use a low ESR
capacitor sized to handle the maximum RMS current.
required to minimize voltage ripple and load step transients.
The Δ V OUT is approximately bounded by:
? 1 ?
?
? 8 ? f OP ? C OUT ?
Since Δ I L increases with input voltage, the output ripple
is highest at maximum input voltage. Typically, once the
ESR requirement is satis?ed, the capacitance is adequate
for ?ltering and has the necessary RMS current rating.
Multiple capacitors placed in parallel may be needed to
meet the ESR and RMS current handling requirements.
Dry tantalum, specialty polymer, aluminum electrolytic
and ceramic capacitors are all available in surface mount
packages. Specialty polymer capacitors offer very low
ESR but have lower speci?c capacitance than other types.
Tantalum capacitors have the highest speci?c capacitance
but it is important to only use types that have been surge
tested for use in switching power supplies. Aluminum
electrolytic capacitors have signi?cantly higher ESR,
but can be used in cost-sensitive applications providing
that consideration is given to ripple current ratings and
long-term reliability. Ceramic capacitors have excellent
low ESR characteristics but can have a high voltage co-
ef?cient and audible piezoelectric effects. The high Q of
ceramic capacitors with trace inductance can also lead to
signi?cant ringing. When used as input capacitors, care
must be taken to ensure that ringing from inrush currents
and switching does not pose an overvoltage hazard to the
power switches and controller. To dampen input voltage
transients, add a small 5μF to 40μF aluminum electrolytic
capacitor with an ESR in the range of 0.5Ω to 2Ω. High
V IN
I RMS ? I OUT ( MAX ) ?
V OUT
V IN
? –1
V OUT
performance though-hole capacitors may also be used,
but an additional ceramic capacitor in parallel is recom-
mended to reduce the effect of lead inductance.
3879f
14
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| LTC3879IMSE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
| LTC3879IMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
| LTC3879IUD#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-QFN 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) |
| LTC3879IUD#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-QFN 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) |
| LTC3880EUJ#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 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:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
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