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| 型号： | LTC3812EFE-5#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 18/34页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16TSSOP |
| 标准包装： | 95 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1MHz |
| 占空比： | 93% |
| 电源电压： | 6.2 V ~ 60 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 ~ 125°C |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 管件 |
| 产品目录页面： | 1336 (CN2011-ZH PDF) |
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LTC3812-5
APPLICATIONS INFORMATION
it is on for only a fraction of the duty cycle. In order for the
diode to be effective, the inductance between it and the
bottom MOSFET must be as small as possible, mandating
that these components be placed adjacently. The diode can
be omitted if the ef?ciency loss is tolerable.
A good approach is to use a combination of aluminum
electrolytics for bulk capacitance and ceramics for low ESR
and RMS current. If the RMS current cannot be handled
by the aluminum capacitors alone, when used together,
the percentage of RMS current that will be supplied by the
aluminum capacitor is reduced to approximately:
INPUT CAPACITOR SELECTION
In continuous mode, the drain current of the top MOSFET
is approximately a square wave of duty cycle V OUT /V IN
% I RMS,ALUM ≈
1
1 + (8 fCR ESR )
2
? 100%
which must be supplied by the input capacitor. To prevent
large input transients, a low ESR input capacitor sized for
the maximum RMS current is given by:
where R ESR is the ESR of the aluminum capacitor and C
is the overall capacitance of the ceramic capacitors. Using
an aluminum electrolytic with a ceramic also helps damp
I O(MAX) OUT
I CIN(RMS)
V
V IN
V IN
V OUT
–1
1/2
the high Q of the ceramic, minimizing ringing .
OUTPUT CAPACITOR SELECTION
This formula has a maximum at V IN = 2V OUT , where I RMS =
I O(MAX) /2. This simple worst-case condition is commonly
used for design because even signi?cant deviations do not
The selection of C OUT is primarily determined by the ESR
required to minimize voltage ripple. The output ripple
( ? V OUT ) is approximately equal to:
offer much relief. Note that the ripple current ratings from
capacitor manufacturers are often based on only 2000
hours of life. This makes it advisable to further derate
V OUT
I L ESR +
1
8fC OUT
the capacitor or to choose a capacitor rated at a higher
temperature than required. Several capacitors may also
be placed in parallel to meet size or height requirements
in the design.
Because tantalum and OS-CON capacitors are not available
in voltages above 30V, ceramics or aluminum electrolytics
must be used for regulators with input supplies above 30V.
Ceramic capacitors have the advantage of very low ESR
and can handle high RMS current, but ceramics with high
voltage ratings (> 50V) are not available with more than
a few microfarads of capacitance. Furthermore, ceram-
ics have high voltage coef?cients which means that the
capacitance values decrease even more when used at the
rated voltage. X5R and X7R type ceramics are recom-
mended for their lower voltage and temperature coef-
?cients. Another consideration when using ceramics is
their high Q which, if not properly damped, may result in
excessive voltage stress on the power MOSFETs. Alumi-
num electrolytics have much higher bulk capacitance, but
they have higher ESR and lower RMS current ratings.
Since ? I L increases with input voltage, the output ripple
is highest at maximum input voltage. ESR also has a sig-
ni?cant effect on the load transient response. Fast load
transitions at the output will appear as voltage across the
ESR of C OUT until the feedback loop in the LTC3812-5 can
change the inductor current to match the new load current
value. Typically, once the ESR requirement is satis?ed the
capacitance is adequate for ?ltering and has the required
RMS current rating.
Manufacturers such as Nichicon, Nippon Chemi-Con
and Sanyo should be considered for high performance
throughhole capacitors. The OS-CON (organic semicon-
ductor dielectric) capacitor available from Sanyo has the
lowest product of ESR and size of any aluminum electroly-
tic at a somewhat higher price. An additional ceramic
capacitor in parallel with OS-CON capacitors is recom-
mended to reduce the effect of their lead inductance.
In surface mount applications, multiple capacitors placed
in parallel may be required to meet the ESR, RMS current
38125fc
18
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| LTC3812IFE-5#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP 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) |
| LTC3812IFE-5#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP 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) |
| LTC3813EG#PBF | 功能描述:IC REG CTRLR BST PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 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 |
| LTC3813EG#TRPBF | 功能描述:IC REG CTRLR BST PWM CM 28-SSOP 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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