AAT3152 datasheet(11/12 Pages) AAT

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AAT3152

High Efficiency 1X/1.5X/2X Charge Pump

For White LED Applications

3152.2005.08.1.2

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 100m

Ω. A value of

1µF for all four capacitors is a good starting point

when choosing capacitors. If the LED current

sources are only programmed for light current lev-

els, then the capacitor size may be decreased.

Capacitor Characteristics

Ceramic composition capacitors are highly recom-

mended over all other types of capacitors for use

with the AAT3152. 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

ceramic capacitors help to maximize charge pump

transient response. Since ceramic capacitors are

non-polarized, they are not prone to incorrect con-

nection damage.

Equivalent Series Resistance

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 typical-

ly measured in milliohms for ceramic capacitors and

can range to more than several ohms for tantalum

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 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

AAT3152 applications. 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.

Thermal Protection

The AAT3152 has a built-in thermal protection cir-

cuit that will shut down the charge pump if the die

temperature rises above the thermal limit, as is the

case during a short circuit of the V

OUT pin.

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