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AAT3113 参数 Datasheet PDF下载

AAT3113图片预览
型号: AAT3113
PDF下载: 下载PDF文件 查看货源
内容描述: 高能效1.5x分数电荷泵为白光LED应用 [High Efficiency 1.5X Fractional Charge Pumps For White LED Applications]
分类和应用:
文件页数/大小: 14 页 / 233 K
品牌: ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
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AAT3113/4  
High Efficiency 1.5X Fractional Charge  
Pumps For White LED Applications  
Power Efficiency and Device Evaluation:  
Capacitor Characteristics  
The charge pump efficiency discussion of the previ-  
ous section only accounts for the efficiency of the  
charge pump section itself. Due to the unique circuit  
architecture and design of the AAT3113/14, it is very  
difficult to measure efficiency in terms of a percent  
value comparing input power over output power.  
Since the AAT3113/14 outputs are pure constant cur-  
rent sources, it is difficult to measure the output volt-  
age for a given output (D1 to D6) to derive an output  
power measurement. For any given application,  
white LED forward voltage levels can differ, yet the  
output drive current will be maintained as a constant.  
This makes quantifying output power a difficult task  
when taken in the context of comparing to other  
white LED driver circuit topologies. A better way to  
quantify total device efficiency is to observe the total  
input power to the device for a given LED current  
drive level. The best White LED driver for a given  
application should be based on trade-offs of size,  
external component count, reliability, operating range  
and total energy usage...Not just "% efficiency".  
Ceramic composition capacitors are highly recom-  
mended over all other types of capacitors for use  
with the AAT3113/4 products. Ceramic capacitors  
offer many advantages over their tantalum and alu-  
minum electrolytic counterparts. A ceramic capaci-  
tor typically has very low ESR, is lowest cost, has a  
smaller PCB footprint and is non-polarized. Low  
ESR ceramic capacitors help maximize charge  
pump transient response. Since ceramic capacitors  
are non-polarized, they are not prone to incorrect  
connection damage.  
Equivalent Series Resistance (ESR): 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, internal  
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 tan-  
talum or aluminum electrolytic capacitors.  
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 stable over tempera-  
ture. Large capacitor values are typically com-  
posed of X7R, X5R, Z5U or Y5V dielectric materi-  
als. Large ceramic capacitors, typically greater  
than 2.2µF are often available in low cost Y5V and  
Z5U dielectrics, but large capacitors are not  
required in the AAT3113/4 application.  
AAT3114 Input Power vs. LED Current  
700  
VIN = 3.6V  
600  
500  
400  
300  
200  
100  
0
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.  
0
20  
40  
60  
80  
100  
120  
140  
Output (LED) Current (mA)  
Capacitor Selection  
Careful selection of the four external capacitors  
CIN, C1, C2, COUT is important because they will  
affect turn on time, output ripple and transient per-  
formance. Optimum performance will be obtained  
when low 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  
capacitors is a good starting point when choosing  
capacitors. If the LED current sources are only  
programmed for minimal current levels, then the  
capacitor size may be decreased.  
Thermal Protection  
The AAT3113/4 have a thermal protection circuit  
that will shut down the charge pump and current  
outputs if the die temperature rises above the ther-  
mal limit. However, thermal resistance of the QFN  
package is so low, that if, in the case of the  
AAT3114, all six outputs are shorted to ground at  
maximum 20mA output level, the die temperature  
will not rise sufficiently to trip the thermal protection.  
The thermal protection will only trip if COUT is short-  
ed to ground and the ambient temperature is high.  
10  
3113.2004.07.1.4