Datasheet > AAT3151B

AAT3151B

更新时间： 2022-04-23 23:00:11

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ANALOGICTECH		泵
页数	文件大小	规格书
15页	266K
描述
High Efficiency 1X/1.5X Charge Pump For White LED Applications

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AAT3151B 数据手册

AAT3151B

High Efficiency 1X/1.5X Charge Pump

For White LED Applications

Capacitor Selection

Equivalent Series Resistance

Careful selection of the four external capacitors

C_IN, C₁, C₂, and C_OUTis important because they will

affect turn-on time, output ripple, and transient per-

formance. Optimum performance will be obtained

when low equivalent series resistance (ESR)

ceramic capacitors are used. In general, low ESR

may be defined as less than 100mΩ. A value of

1µF for all four capacitors is a good starting point

when choosing capacitors. If the constant current

sinks are only programmed for light current levels,

then the capacitor size may be decreased.

ESR is an important characteristic to consider when

selecting a capacitor. ESR is a resistance internal

to a capacitor that 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 tanta-

lum or aluminum electrolytic capacitors.

Ceramic Capacitor Materials

Ceramic capacitors less than 0.1µF are typically

made from NPO or C0G materials. NPO and C0G

materials generally have tight tolerance and are

very stable over temperature. Larger capacitor val-

ues are usually composed of X7R, X5R, Z5U, or

Y5V dielectric materials. Large ceramic capacitors

(i.e., greater than 2.2µF) are often available in low-

cost Y5V and Z5U dielectrics, but capacitors

greater than 1µF are not typically required for

AAT3151B applications.

Capacitor Characteristics

Ceramic composition capacitors are highly recom-

mended over all other types of capacitors for use

with the AAT3151B. Ceramic capacitors offer

many advantages over their tantalum and alu-

minum electrolytic counterparts. A ceramic capac-

itor has very low ESR, is lowest cost, has a small-

er 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 con-

nection damage.

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.

3151B.2007.09.1.0

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