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AAT3151DFN33-12 参数 Datasheet PDF下载

AAT3151DFN33-12图片预览
型号: AAT3151DFN33-12
PDF下载: 下载PDF文件 查看货源
内容描述: [Interface Circuit,]
分类和应用:
文件页数/大小: 12 页 / 169 K
品牌: ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
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AAT3151  
High Efficiency 1X/1.5X/2X Charge Pump  
For White LED Applications  
For a charge pump with an output of 5 volts and a  
ceramic capacitors help maximize charge pump  
transient response. Since ceramic capacitors are  
non-polarized, they are not prone to incorrect con-  
nection damage.  
nominal input of 3.5 volts, the theoretical efficiency  
is 95%. Due to internal switching losses and IC  
quiescent current consumption, the actual efficien-  
cy can be measured at 93%. These figures are in  
close agreement for output load conditions from  
1mA to 100mA. Efficiency will decrease as load  
current drops below 0.05mA or when level of VIN  
Equivalent Series Resistance  
ESR is an important characteristic to consider when  
selecting a capacitor. ESR is a resistance internal  
to a capacitor, which is caused by the leads, inter-  
nal connections, size or area, material composition,  
and ambient temperature. Capacitor ESR is typi-  
cally measured in milliohms for ceramic capacitors  
and can range to more than several ohms for tanta-  
lum or aluminum electrolytic capacitors.  
approaches VOUT  
.
Capacitor Selection  
Careful selection of the four external capacitors  
CIN, C1, C2, and COUT is important because they  
will affect turn-on time, output ripple, and transient  
performance. Optimum performance will be  
obtained when low equivalent series resistance  
(ESR) (<100m) ceramic capacitors are used. In  
general, low ESR may be defined as less than  
100m. A capacitor value of 1µF for all four capac-  
itors is a good starting point when choosing capac-  
itors. If the constant current sinks are only pro-  
grammed for light current levels, then the capacitor  
size may be decreased.  
Ceramic Capacitor Materials  
Ceramic capacitors less than 0.1µF are typically  
made from NPO or COG materials. NPO and COG  
materials typically have tight tolerance and are sta-  
ble over temperature. Larger capacitor values are  
typically composed of X7R, X5R, Z5U, or Y5V  
dielectric materials. Large ceramic capacitors, typ-  
ically greater than 2.2µF, are often available in low-  
cost Y5V and Z5U dielectrics, but capacitors  
greater than 1µF are typically not required for  
AAT3151 applications.  
Capacitor Characteristics  
Ceramic composition capacitors are highly recom-  
mended over all other types of capacitors for use  
with the AAT3151. Ceramic capacitors offer many  
advantages over their tantalum and aluminum elec-  
trolytic counterparts. A ceramic capacitor typically  
has very low ESR, is lowest cost, has a smaller  
PCB footprint, and is non-polarized. Low ESR  
Capacitor area is another contributor to ESR.  
Capacitors that are physically large will have a lower  
ESR when compared to an equivalent material  
smaller capacitor. These larger devices can improve  
circuit transient response when compared to an  
equal value capacitor in a smaller package size.  
3151.2004.10.0.6  
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