AAT3129
High Efficiency 1X/1.5X/2X Charge Pump
for RGB Color LED Applications
Mode Register Settings - Address 5
M Setting
Action
1
2
R, G, B, T Registers Latched Independently
R, G, B Registers Synchronized to T Register Latch
LED Current
The resulting DC current for each of the R, G, and B channels depends on the overall system settings. Using the
overall settings, the current for a particular channel is calculated as
R - 1
IR = ISRC
IG = ISRC
IB = ISRC
·
·
·
4 · (T - 1) + (R - 1) + (G - 1) + (B - 1) + CHLS_ON
G - 1
4 · (T - 1) + (R - 1) + (G - 1) + (B - 1) + CHLS_ON
B - 1
4 · (T - 1) + (R - 1) + (G - 1) + (B - 1) + CHLS_ON
where ISRC is the factory programmed current and
CHLS_ON is the number of channels programmed
to operate. Whenever a channel is programmed to
Data = 1, that channel is programmed to off and
must be removed from the CHLS_ON count.
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3129. Ceramic capacitors offer many
advantages over their tantalum and aluminum
electrolytic counterparts. A ceramic capacitor typi-
cally 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 Selection
Careful selection of the four external capacitors
CIN, C1, C2, and COUT is important because they
will affect turn-on time, output ripple, and transient
performance. 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. For best
overall performance, 1μF capacitors are recom-
mended. Depending on ripple requirements, the
input and output capacitor values can be increased
or decreased accordingly. If lower ripple is desired,
increase the capacitor value. The peak-to-peak rip-
ple seen at the input or output increases or
decreases with capacitor size.
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.
12
3129.2007.01.1.4
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
