AAT3113,AAT3114/14A

High Efficiency 1.5X Fractional Charge Pumps For White LED Applications

PRODUCT DATASHEET

3113.2008.05.1.10

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Output (LED) Current (mA)

Figure 3: AAT3113/AAT3114 Input Power

vs. LED Current

Capacitor Selection

time, output ripple, and transient performance. Optimum

performance will be obtained when low equivalent series

resistance (ESR) ceramic capacitors are used. In gen-

eral, 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 LED current

sources are only programmed for minimal current levels,

then the capacitor size may be decreased.

Capacitor Characteristics

Ceramic composition capacitors are highly recommend-

ed over all other types of capacitors for use with the

AAT3113 and AAT3114/14A products. Ceramic capaci-

tors offer many advantages over their tantalum and

aluminum electrolytic 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 maximize charge pump transient

response. Since ceramic capacitors are non-polarized,

they are not prone to incorrect connection 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 connec-

tions, size or area, material composition, and ambient

temperature. Capacitor ESR is typically measured in mil-

liohms 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

generally have tight tolerance and are very stable over

temperature. Larger capacitor values are usually com-

posed 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

AAT3113 or AAT3114/14A 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.

Test Current/Channel Disable

Each channel of the output is equipped with a test cur-

rent function. The AAT3113 and AAT3114 use a small

(~2µA) current source injected into each output pin to

detect the presence of an LED. Unused channels other

than channel 1 should be left open and will be automati-

cally diasbled instead of wasting the programmed output

current. The test current in the AAT3114A is higher

(~150µA) to accommodate LEDs with lower impedance

in failure mode.

Thermal Protection

The AAT3113 and AAT3114/14A have a thermal protec-

tion circuit that will shut down the charge pump and

current outputs if the die temperature rises above the

thermal limit. However, thermal resistance of the QFN

package is so low that if, in the case of the AAT3114/14A,

all six outputs are shorted to ground at maximum 20mA

output level, the die temperature will not rise sufficient-

ly to trip the thermal protection. The thermal protection

temperature is high.