AAT3152 Datasheet, PDF (9/10 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications

AAT3152
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
performance. Optimum performance will be
obtained when low Equivalent Series Resistance
(ESR) (<100mΩ) ceramic capacitors are used. In
general, low ESR may be defined as less than
100mΩ. A capacitor value of 1µF for all four capac-
itors is a good starting point when choosing capac-
itors. If the LED current sources are only pro-
grammed for light current levels, 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, which 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 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
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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