AAT3164 Datasheet, PDF (12/14 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X/2X Charge Pump for Six-Channel White LED Applications

AAT3164
High Efficiency 1X/1.5X/2X Charge Pump for
Six-Channel White LED Applications
1µF
1µF
C1+ C1- C2+ C2-
IN
OUT
VBAT
AAT 3164
CIN
COUT
1µF
1µF
GND
D1
EN/SET
EN/SET
D2
D3
D4
RSET
D5
D6
26.1K
3 LED pack
80mA
each
Figure 5: Configuration for a Typical Three-LED Application.
Device Switching Noise Performance
The AAT3164 operates at a fixed frequency of
approximately 1MHz to control noise and limit har-
monics that can interfere with the RF operation of
cellular telephone handsets or other communica-
tion devices. Back-injected noise appearing on the
input pin of the charge pump is 20mV peak-to-
peak, typically ten times less than inductor-based
DC/DC boost converter white LED backlight solu-
tions. The AAT3164 soft-start feature prevents
noise transient effects associated with inrush cur-
rents during start-up of the charge pump circuit.
Capacitor Selection
Careful selection of the four external capacitors
C_IN, C₁, C₂, and C_OUT is 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 LED current
sources are only programmed for light current lev-
els, then the capacitor value may be decreased.
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use with
the AAT3164. Ceramic capacitors offer many advan-
tages 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 connections, size or area, material compo-
sition, and ambient temperature. Capacitor ESR is
typically measured in milliohms for ceramic capac-
itors 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 composed of X7R, X5R, Z5U, or Y5V dielec-
tric 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 AAT3164 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.
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3164.2006.07.1.0